We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units, one
of which will be ours. The electrical supply comes into the unit that will
not be ours, so the landlord is putting a new supply into our bit for us as
part of the deal. The currently installed supply is three phase, with each
phase company-fused at 100A, as far as I can see. We have approached NPower
for a meter, and one of the questions on the application form refers to the
type of meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".

I have not the slightest idea what the difference between these is, or which
it will be that we need ?? I have checked with the landlord to make sure
that it is a three phase supply that he is bringing over to our unit, and he
says that we will "need a three phase meter for a 40kVA supply" First
question then. If each phase is currently fused at 100A, does that mean that
the incoming supply is 25kVA per phase i.e. 75kVA, and that by dividing it
between the two newly created premises, that is how he arrives at 40kVA ?

Our demand will be fairly high. There will be two electrical fryers, each
loading at 2 x 9kW, so I guess if they are all on and heating up together,
that would be a demand of 36kW. There is also a ceiling mounted airco /
heater unit that I don't know the specs for . It's not very big - maybe 2 ft
square. Other than that, the demand will be moderately low - some fume
extraction which is only a few amps, a couple of small fridges and freezers,
lights (not more than 1kW) and small odds and sods for a normal ring main.
So, given the *potential* for everything being on together, does that mean
that the supply he is proposing giving us, is going to be adequate for our
needs ?

Another question on the form is "Voltage - please delete" The three options
given are 415V 11kV and 33kV. I assume that the correct answer there is 415V
as it's a three phase supply direct into the premises ?

Help please, lads ... !! d:-)

TIA

Arfa

"Arfa Daily" wrote in message
...
We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units, one
of which will be ours. The electrical supply comes into the unit that will
not be ours, so the landlord is putting a new supply into our bit for us
as part of the deal. The currently installed supply is three phase, with
each phase company-fused at 100A, as far as I can see. We have approached
NPower for a meter, and one of the questions on the application form
refers to the type of meter required. The two three phase options given
are "Three Phase Whole Current" and "Three Phase CT".

I have not the slightest idea what the difference between these is, or
which it will be that we need ?? I have checked with the landlord to make
sure that it is a three phase supply that he is bringing over to our unit,
and he says that we will "need a three phase meter for a 40kVA supply"
First question then. If each phase is currently fused at 100A, does that
mean that the incoming supply is 25kVA per phase i.e. 75kVA, and that by
dividing it between the two newly created premises, that is how he arrives
at 40kVA ?

Our demand will be fairly high. There will be two electrical fryers, each
loading at 2 x 9kW, so I guess if they are all on and heating up together,
that would be a demand of 36kW. There is also a ceiling mounted airco /
heater unit that I don't know the specs for . It's not very big - maybe 2
ft square. Other than that, the demand will be moderately low - some fume
extraction which is only a few amps, a couple of small fridges and
freezers, lights (not more than 1kW) and small odds and sods for a normal
ring main. So, given the *potential* for everything being on together,
does that mean that the supply he is proposing giving us, is going to be
adequate for our needs ?

Another question on the form is "Voltage - please delete" The three
options given are 415V 11kV and 33kV. I assume that the correct answer
there is 415V as it's a three phase supply direct into the premises ?

Just a query in passing - IIUC you can get industrial machinery (such as
lathes, drills etc.) which run on 3 phase directly - which would obviously
require three phases.

If you have normal 230V kit do you have two supplies of 230V split between
the three phases when you install a 3 phase supply?

Cheers

Dave R

On 13/04/2011 19:00, David WE Roberts wrote:

Just a query in passing - IIUC you can get industrial machinery (such as
lathes, drills etc.) which run on 3 phase directly - which would
obviously require three phases.

If you have normal 230V kit do you have two supplies of 230V split
between the three phases when you install a 3 phase supply?

Cheers

Dave R

No, a 3-phase supply will come as 4 wires: L1, L2, L3 and N.

Each phase ( L1, L2, L3 ) to N is a standard 240v supply.
Phase-to-Phase is 415v.

( Give or take the EU harmonisation voltages etc.. )

So you can feed 3-phase motors etc off L1, L2, L3. They typically
won't require the N.

The dist board will have a 3-phase incomer, and 3 L bus-bars. 3-pole
breakers will connect to each of the L to feed 3-ph loads. Single-pole
MCBs will connect to only one L, and the single-phase wiring will then
use the N bar, just like a domestic CU.

--
Ron

Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq ft
units, one of which will be ours. The electrical supply comes into
the unit that will not be ours, so the landlord is putting a new
supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter, and
one of the questions on the application form refers to the type of
meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? I have checked with the landlord
to make sure that it is a three phase supply that he is bringing over
to our unit, and he says that we will "need a three phase meter for a
40kVA supply" First question then. If each phase is currently fused
at 100A, does that mean that the incoming supply is 25kVA per phase
i.e. 75kVA, and that by dividing it between the two newly created
premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating up
together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will be
moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the *potential*
for everything being on together, does that mean that the supply he
is proposing giving us, is going to be adequate for our needs ?

Another question on the form is "Voltage - please delete" The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A fuses on a 3
phase supply does not give you 300A of available power for 230V appliances
(no matter how well you share the load between the fuses) as the neutral is
only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the nominal
voltage between phases) by the 100A fuse. ISTR that it should be multiplied
by sq rt of 3 to get the maximum power.


With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

--
Cheers
Adam

On Apr 13, 5:20*pm, "Arfa Daily" wrote:
We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units, one
of which will be ours. The electrical supply comes into the unit that will
not be ours, so the landlord is putting a new supply into our bit for us as
part of the deal. The currently installed supply is three phase, with each
phase company-fused at 100A, as far as I can see. We have approached NPower
for a meter, and one of the questions on the application form refers to the
type of meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".

I have not the slightest idea what the difference between these is, or which
it will be that we need ?? *I have checked with the landlord to make sure
that it is a three phase supply that he is bringing over to our unit, and he
says that we will "need a three phase meter for a 40kVA supply" First
question then. If each phase is currently fused at 100A, does that mean that
the incoming supply is 25kVA per phase i.e. 75kVA, and that by dividing it
between the two newly created premises, that is how he arrives at 40kVA ?

Our demand will be fairly high. There will be two electrical fryers, each
loading at 2 x 9kW, so I guess if they are all on and heating up together,
that would be a demand of 36kW. There is also a ceiling mounted airco /
heater unit that I don't know the specs for . It's not very big - maybe 2 ft
square. Other than that, the demand will be moderately low - some fume
extraction which is only a few amps, a couple of small fridges and freezers,
lights (not more than 1kW) and small odds and sods for a normal ring main..
So, given the *potential* for everything being on together, does that mean
that the supply he is proposing giving us, is going to be adequate for our
needs ?

Another question on the form is "Voltage - please delete" The three options
given are 415V 11kV and 33kV. I assume that the correct answer there is 415V
as it's a three phase supply direct into the premises ?

Help please, lads ... !! * * *d:-)

TIA

Arfa

Whole current means the meters pass the whole current through them (as
you might think).

CT=current transformer. For large industrial supplies. The current
passes through a Current Transormer which reduces the cureent to
usually 5amp max, There are different ratios on the CT eg 50:1 would
be a 250 amp supply.
100:1 would be a 500amp supply. etc.

I should think each flat would be given a single phase supply, 100a is
ample.
You will be "whole current"

On Apr 13, 7:37*pm, "ARWadsworth"
wrote:
Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq ft
units, one of which will be ours. The electrical supply comes into
the unit that will not be ours, so the landlord is putting a new
supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter, and
one of the questions on the application form refers to the type of
meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? *I have checked with the landlord
to make sure that it is a three phase supply that he is bringing over
to our unit, and he says that we will "need a three phase meter for a
40kVA supply" First question then. If each phase is currently fused
at 100A, does that mean that the incoming supply is 25kVA per phase
i.e. 75kVA, and that by dividing it between the two newly created
premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating up
together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will be
moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the *potential*
for everything being on together, does that mean that the supply he
is proposing giving us, is going to be adequate for our needs ?

Another question on the form is "Voltage - please delete" The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A fuses on a 3
phase supply does not give you 300A of available power for 230V appliances
(no matter how well you share the load between the fuses) as the neutral is
only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the nominal
voltage between phases) by the 100A fuse. ISTR that it should be multiplied
by sq rt of 3 to get the maximum power.

With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced.

harry wrote:
On Apr 13, 7:37 pm, "ARWadsworth"
wrote:
Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq
ft units, one of which will be ours. The electrical supply comes
into the unit that will not be ours, so the landlord is putting a
new supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter,
and one of the questions on the application form refers to the type
of meter required. The two three phase options given are "Three
Phase Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? I have checked with the landlord
to make sure that it is a three phase supply that he is bringing
over to our unit, and he says that we will "need a three phase
meter for a 40kVA supply" First question then. If each phase is
currently fused at 100A, does that mean that the incoming supply is
25kVA per phase i.e. 75kVA, and that by dividing it between the two
newly created premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating
up together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will
be moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the
*potential* for everything being on together, does that mean that
the supply he is proposing giving us, is going to be adequate for
our needs ?

Another question on the form is "Voltage - please delete" The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A
fuses on a 3 phase supply does not give you 300A of available power
for 230V appliances (no matter how well you share the load between
the fuses) as the neutral is only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the
nominal voltage between phases) by the 100A fuse. ISTR that it
should be multiplied by sq rt of 3 to get the maximum power.

With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced.

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced.

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

newshound wrote:
--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current
at all.
A neutral current only appears when the phase currents are
unbalanced.

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

No there would not be 300A in the neutral.


--
Adam

newshound wrote:

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced.

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

I calculate it that if you have all three phases drawing 100A, the
neutral would be carrying only stray currents, but if only one phase was
loaded, the neutral current would be equal to the load current. With two
running, it's something on the order of 1/ (square root of 2) multiplied
by the combined load current, so in this case about 141A maximum with
full load on two phases. With three phases running in balance, it's
close to zero. It's a vector sum, and the worst case is with two phases
running at full load, and the other one drawing zero load. For other
combinations, it depends on the loads on each phase.

--
Tciao for Now!

John.

John Williamson wrote:
newshound wrote:

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current
at all.
A neutral current only appears when the phase currents are
unbalanced.

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

I calculate it that if you have all three phases drawing 100A, the
neutral would be carrying only stray currents, but if only one phase
was loaded, the neutral current would be equal to the load current.
With two running, it's something on the order of 1/ (square root of
2) multiplied by the combined load current, so in this case about
141A maximum with full load on two phases. With three phases running
in balance, it's close to zero. It's a vector sum, and the worst case
is with two phases running at full load, and the other one drawing
zero load. For other combinations, it depends on the loads on each
phase.

I was having a brain dead moment. My apologies to Harry.

Depending on the balancing of the system there could be a higher current in
the neutral than 100A and that is what I was thinking of.

I stand corrected. I was wrong and I admit it.

--
Adam

"ARWadsworth" wrote in message
...

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

Do pay attention, he has two 9 kW fryers, they are not going to be 230V.
Even the dishwasher I put in was three phase and that was only 7 kW.
And no I don't know enough about 3 phase to answer the OPs questions.

On 13/04/2011 17:20, Arfa Daily wrote:
snip
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating up
together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's not
very big - maybe 2 ft square.
/snip

Find the specs for that aircon unit. I'd expect it to use a substantial
fraction of the heat it needs to get rid of - and on a hot summer's day
that will be the whole 36kW and a bit. I'm no expert (I merely suffer
these things in computer rooms) but I wouldn't be at all surprised to
find it eats another 18kW.

Seems to me that may exceed your power limit.

Splitting this lot evenly over three phases isn't going to be possible.
Some of the time you'll have load on one of the phases only, sometimes
two, and only occasionally all three.

Andy.

In article , dennis@home
writes

Do pay attention

No thanks. re-plonked due to morph.

--
(\__/)
(='.'=)
(")_(")

On Apr 13, 5:20*pm, "Arfa Daily" wrote:
We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units, one
of which will be ours. The electrical supply comes into the unit that will
not be ours, so the landlord is putting a new supply into our bit for us as
part of the deal. The currently installed supply is three phase, with each
phase company-fused at 100A, as far as I can see. We have approached NPower
for a meter, and one of the questions on the application form refers to the
type of meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".


Another question on the form is "Voltage - please delete" The three options
given are 415V 11kV and 33kV. I assume that the correct answer there is 415V
as it's a three phase supply direct into the premises ?

Help please, lads ... !! * * *d:-)

TIA

Arfa

40 Kva is approx 53 amps/phase,so he is trying to split the available
power equally between the two units.
At that level you want the "whole current" and 415v options.

Owain wrote:

I suspect that at 3 x 100A you'd use Whole Current metering unless
there's a good reason not to.

Yes I think so, up to 72kVA per MPAN(meter point access number) which is
111A per phase whole current metering is allowed beyond that it gets
complicated with paying for the supply depending on time of day etc,

To avoid this I decided to split our units into two separately fed sections
each with 100A 3ph.

AJH

In message , ARWadsworth
writes
Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq ft
units, one of which will be ours. The electrical supply comes into
the unit that will not be ours, so the landlord is putting a new
supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter, and
one of the questions on the application form refers to the type of
meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? I have checked with the landlord
to make sure that it is a three phase supply that he is bringing over
to our unit, and he says that we will "need a three phase meter for a
40kVA supply" First question then. If each phase is currently fused
at 100A, does that mean that the incoming supply is 25kVA per phase
i.e. 75kVA, and that by dividing it between the two newly created
premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating up
together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will be
moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the *potential*
for everything being on together, does that mean that the supply he
is proposing giving us, is going to be adequate for our needs ?

Another question on the form is "Voltage - please delete" The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A fuses on a 3
phase supply does not give you 300A of available power for 230V appliances
(no matter how well you share the load between the fuses) as the neutral is
only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the nominal
voltage between phases) by the 100A fuse. ISTR that it should be multiplied
by sq rt of 3 to get the maximum power.


With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

You forgot Harry ...

--
geoff

geoff wrote:
In message , ARWadsworth
writes
Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq
ft units, one of which will be ours. The electrical supply comes
into the unit that will not be ours, so the landlord is putting a
new supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter,
and one of the questions on the application form refers to the type
of meter required. The two three phase options given are "Three
Phase Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? I have checked with the
landlord to make sure that it is a three phase supply that he is
bringing over to our unit, and he says that we will "need a three
phase meter for a 40kVA supply" First question then. If each phase
is currently fused at 100A, does that mean that the incoming supply
is 25kVA per phase i.e. 75kVA, and that by dividing it between the
two newly created premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating
up together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will
be moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the
*potential* for everything being on together, does that mean that
the supply he is proposing giving us, is going to be adequate for
our needs ? Another question on the form is "Voltage - please delete"
The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A
fuses on a 3 phase supply does not give you 300A of available power
for 230V appliances (no matter how well you share the load between
the fuses) as the neutral is only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the
nominal voltage between phases) by the 100A fuse. ISTR that it
should be multiplied by sq rt of 3 to get the maximum power.


With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

You forgot Harry ...

No, I didn't.

And I was wrong. I offered my apologies to Harry. What more can you do? I
was wrong and I admitted it.

I will not try to make excuses, I will eat humble pie.

--
Adam

On 13/04/2011 17:43, Owain wrote:

I suspect that at 3 x 100A you'd use Whole Current metering unless
there's a good reason not to.

Surely it's the supplier's or metering company's decision what type of
metering to install? (Consumer chooses tariff, supplier installs
appropriate metering equipment of their choice.)

Round here (the old Eastern region) they tend to use whole-current
metering up to 3 x 200 A and CTs for larger. If you find CTs on smaller
supplies it's generally where old meter equipment hasn't been updated.

--
Andy

On 13/04/2011 20:54, ARWadsworth wrote:

I was having a brain dead moment. My apologies...

I was waiting for the penny to drop. . .

What you do have to watch though is non-linear loads (old iron-cored
fluorescent ballasts, for example) where the 3rd and 9th, etc. harmonics
add in in the neutral, even when the load is perfectly balanced. The
17th ed. requires double-size neutrals in some circumstances. Checking
neutral current with a clamp meter (preferably true-RMS reading) is
always a wise precaution on 3-ph work.

--
Andy

"mark" wrote in message
...
On Apr 13, 5:20 pm, "Arfa Daily" wrote:
We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units,
one
of which will be ours. The electrical supply comes into the unit that
will
not be ours, so the landlord is putting a new supply into our bit for us
as
part of the deal. The currently installed supply is three phase, with
each
phase company-fused at 100A, as far as I can see. We have approached
NPower
for a meter, and one of the questions on the application form refers to
the
type of meter required. The two three phase options given are "Three
Phase
Whole Current" and "Three Phase CT".


Another question on the form is "Voltage - please delete" The three
options
given are 415V 11kV and 33kV. I assume that the correct answer there is
415V
as it's a three phase supply direct into the premises ?

Help please, lads ... !! d:-)

TIA

Arfa

40 Kva is approx 53 amps/phase,so he is trying to split the available
power equally between the two units.
At that level you want the "whole current" and 415v options.


OK. Thanks for all the useful information, everyone. Looks like I need to do
a bit more research. I just went looking at the detailed specs for the
proposed fryers, and interestingly, it states neither a supply voltage nor a
phase requirement. Only that it is 2 x 9kW. I must admit that I never even
considered that they might be three phase. I have now shot an email off to
the manufacturers to enquire on this point.

However, when I was reading up on them, it seems to me that the proposed
model has way more capacity than we are going to require. My daughter has
specced all of the equipment, and I'm not sure quite how she arrived at this
model. I will ask her tomorrow, as from what I can see, the manufacturer has
models of much more modest power requirements, that would easily be able to
keep up with the demand that's going to be placed on them.

Arfa

In article , Arfa Daily
writes

from what I can see, the manufacturer has
models of much more modest power requirements, that would easily be able to
keep up with the demand that's going to be placed on them.

If the 9kW model your daughter has (over)specced is single-phase, rather
than install two of those, you might be able to settle on three smaller
single-phase models, one on each phase, to help with load balancing.

--
(\__/)
(='.'=)
(")_(")

On 13/04/2011 21:15, dennis@home wrote:


"ARWadsworth" wrote in message
...

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

Do pay attention, he has two 9 kW fryers, they are not going to be 230V.
Even the dishwasher I put in was three phase and that was only 7 kW.
And no I don't know enough about 3 phase to answer the OPs questions.

Is that 9kW including VAT or plus VAT?


--
Dave - The Medway Handyman www.medwayhandyman.co.uk

"Owain" wrote in message
...
On Apr 13, 9:15 pm, "dennis@home" wrote:
Not if the OP is only using 230V appliances.
Please pay attention to what is written.
Do pay attention, he has two 9 kW fryers, they are not going to be 230V.
Even the dishwasher I put in was three phase and that was only 7 kW.

I've got a 10kW shower in my bathroom. It's definately not three-
phase.

Its not going to be on for hours at a time.
Three phase kitchen stuff tends to be cheaper than single phase and the
cables are smaller too.
When you need to start wiring it up you will soon wish it were 3 phase if
you special ordered single phase stuff.

"Mike Tomlinson" wrote in message
news
In article , Arfa Daily
writes

from what I can see, the manufacturer has
models of much more modest power requirements, that would easily be able
to
keep up with the demand that's going to be placed on them.

If the 9kW model your daughter has (over)specced is single-phase, rather
than install two of those, you might be able to settle on three smaller
single-phase models, one on each phase, to help with load balancing.

I would love to see the maths on that..
three fryers all operating their own heating cycle, based on when you
switched them on, how much and what type of food you put in, etc. They could
end up in phase or out of phase with each other for unknown periods of time
as they cycle. An electricians nightmare IMO, but that's diversity for you.

I would just ensure they were three phase so all the heaters were on at the
same time whatever you put in them.

Being as I can cook a bit I can also understand why she would want a high
power input too, you don't want it to keep going cold every time you chuck
some food in. You want a fast recovery time to ensure it frys properly and
to increase throughput potential.

On Wed, 13 Apr 2011 17:20:06 +0100, Arfa Daily wrote:

More or less definitive answer coming up......


We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units, one
of which will be ours. The electrical supply comes into the unit that will
not be ours, so the landlord is putting a new supply into our bit for us as
part of the deal. The currently installed supply is three phase, with each
phase company-fused at 100A, as far as I can see. We have approached NPower
for a meter, and one of the questions on the application form refers to the
type of meter required. The two three phase options given are "Three Phase
Whole Current" and "Three Phase CT".

Right, 3 x 100a supply equates to a nominal maximum capacity of 75 kva.
First thing, you need to do is determine your maximum demand allowing for
diversity. Will everything be on and working at once? Do the fryers cycle
because of thermostats. I'm guessing you're probably going to be looking an
MD of about 40-50 kva.

Whole current means the installation is connected directly through the
meter. A three phase WC meter will have a maximum capacity of about 80 to
100 amps per phase.

If you were going for some major industrial process with motors, heating
welding and all sorts of other equipment you could be looking at a demand
well in excess of 100a per phase. These meters operate using CTs (current
transformers), usually 200/5 or 400/5, so the meter is actually taking only
a small percentage of the full load current. The incoming cable and main
fuses are also much larger.

I have not the slightest idea what the difference between these is, or which
it will be that we need ??

See above

I have checked with the landlord to make sure
that it is a three phase supply that he is bringing over to our unit, and he
says that we will "need a three phase meter for a 40kVA supply" First
question then. If each phase is currently fused at 100A, does that mean that
the incoming supply is 25kVA per phase i.e. 75kVA, and that by dividing it
between the two newly created premises, that is how he arrives at 40kVA ?

Is this a completely new supply or is he extending the installation to give
you a sub-main off the existing installation? If that's the case, you'll be
paying the landlord through a private meter, nothing to do with the
distribution company.

Our demand will be fairly high. There will be two electrical fryers, each
loading at 2 x 9kW, so I guess if they are all on and heating up together,
that would be a demand of 36kW. There is also a ceiling mounted airco /
heater unit that I don't know the specs for . It's not very big - maybe 2 ft
square. Other than that, the demand will be moderately low - some fume
extraction which is only a few amps, a couple of small fridges and freezers,
lights (not more than 1kW) and small odds and sods for a normal ring main.
So, given the *potential* for everything being on together, does that mean
that the supply he is proposing giving us, is going to be adequate for our
needs ?

Another question on the form is "Voltage - please delete" The three options
given are 415V 11kV and 33kV. I assume that the correct answer there is 415V
as it's a three phase supply direct into the premises ?


415 volts, but see above.



--
The Wanderer

When you hear the toilet flush and your child says 'Uh oh'
It's already too late!

On Apr 13, 8:43*pm, John Williamson
wrote:
newshound wrote:

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced..

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

I calculate it that if you have all three phases drawing 100A, the
neutral would be carrying only stray currents, but if only one phase was
loaded, the neutral current would be equal to the load current. With two
running, it's something on the order of 1/ (square root of 2) multiplied
by the combined load current, so in this case about 141A maximum with
full load on two phases. With three phases running in balance, it's
close to zero. It's a vector sum, and the worst case is with two phases
running at full load, and the other one drawing zero load. For other
combinations, it depends on the loads on each phase.

I think you'll find that with resistive loads (which would seem to be
what we'd have with fryers - most of the power into heating elements)
the vector sum for two phases drawing 100 Amps each will still be 100A
- which is why when you add the third phase it just cancels that out
to give no current in the supply neutral.
What Adam may have been thinking of is that in some circumstances the
power factors on the three phases could be diffferent when supplying
single phase loads, and that could certainly result in more than 100A
neutral current if the difference was extreme enough. A piece of three
phase kit would normally be expected to have similar power factor on
all three phases, so the neutral currents would balance.

--

Mike

docholliday wrote:
On Apr 13, 8:43 pm, John Williamson
wrote:
newshound wrote:

--
Cheers
Adam- Hide quoted text -
- Show quoted text -
If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced.
Not if the OP is only using 230V appliances.
Please pay attention to what is written.
--
Adam
I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?
I calculate it that if you have all three phases drawing 100A, the
neutral would be carrying only stray currents, but if only one phase was
loaded, the neutral current would be equal to the load current. With two
running, it's something on the order of 1/ (square root of 2) multiplied
by the combined load current, so in this case about 141A maximum with
full load on two phases. With three phases running in balance, it's
close to zero. It's a vector sum, and the worst case is with two phases
running at full load, and the other one drawing zero load. For other
combinations, it depends on the loads on each phase.

I think you'll find that with resistive loads (which would seem to be
what we'd have with fryers - most of the power into heating elements)
the vector sum for two phases drawing 100 Amps each will still be 100A
- which is why when you add the third phase it just cancels that out
to give no current in the supply neutral.

I calculated for resistive loads, what I omitted was any calculation of
the effect that lagging and leading load factors on different phases
would have. In extreme cases, that could make the maximum neutral
current approach or even exceed 200A if only two phases are drawing
power, with one having a 100% leading factor and the other 100% lagging.
Of course, it depends *which* phase is leading and which is lagging. The
sum could be very close to zero. The calculations get a bit hairy, though.

What Adam may have been thinking of is that in some circumstances the
power factors on the three phases could be diffferent when supplying
single phase loads, and that could certainly result in more than 100A
neutral current if the difference was extreme enough. A piece of three
phase kit would normally be expected to have similar power factor on
all three phases, so the neutral currents would balance.

See above, but there are no circumstances it would be 300A under normal
running with all 3 phases drawing power.

Tciao for Now!

John.

On 14/04/2011 11:07, docholliday wrote:

the vector sum for two phases drawing 100 Amps each will still be 100A
- which is why when you add the third phase it just cancels that out
to give no current in the supply neutral.

Correct.

--
Andy

On Apr 13, 7:59*pm, "ARWadsworth"
wrote:
harry wrote:
On Apr 13, 7:37 pm, "ARWadsworth"
wrote:
Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq
ft units, one of which will be ours. The electrical supply comes
into the unit that will not be ours, so the landlord is putting a
new supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter,
and one of the questions on the application form refers to the type
of meter required. The two three phase options given are "Three
Phase Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? I have checked with the landlord
to make sure that it is a three phase supply that he is bringing
over to our unit, and he says that we will "need a three phase
meter for a 40kVA supply" First question then. If each phase is
currently fused at 100A, does that mean that the incoming supply is
25kVA per phase i.e. 75kVA, and that by dividing it between the two
newly created premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating
up together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will
be moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the
*potential* for everything being on together, does that mean that
the supply he is proposing giving us, is going to be adequate for
our needs ?

Another question on the form is "Voltage - please delete" The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A
fuses on a 3 phase supply does not give you 300A of available power
for 230V appliances (no matter how well you share the load between
the fuses) as the neutral is only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the
nominal voltage between phases) by the 100A fuse. ISTR that it
should be multiplied by sq rt of 3 to get the maximum power.

With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced.

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam- Hide quoted text -

- Show quoted text -

It matters not If all were using the same Kw, Where the separate
neutral wires meet, the sum is zero.

On Apr 13, 8:43*pm, John Williamson
wrote:
newshound wrote:

--
Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced..

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

--
Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

I calculate it that if you have all three phases drawing 100A, the
neutral would be carrying only stray currents, but if only one phase was
loaded, the neutral current would be equal to the load current. With two
running, it's something on the order of 1/ (square root of 2) multiplied
by the combined load current, so in this case about 141A maximum with
full load on two phases. With three phases running in balance, it's
close to zero. It's a vector sum, and the worst case is with two phases
running at full load, and the other one drawing zero load. For other
combinations, it depends on the loads on each phase.

--
Tciao for Now!

John.- Hide quoted text -

- Show quoted text -

No. you're also wrong. The power factor in each circuit would need to
be taken into account same also for the sum to be zero. eg three
identicle loads.
But three identicle currents @120eg apart is only one possible option.

There are others. If one phase was running lagging for example the
sum could still be zero. but the currents in the other two phases
would be different.

On Apr 13, 9:21*pm, Andy Champ wrote:
On 13/04/2011 17:20, Arfa Daily wrote:
snip Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating up
together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's not
very big - maybe 2 ft square.

/snip

Find the specs for that aircon unit. *I'd expect it to use a substantial
fraction of the heat it needs to get rid of - and on a hot summer's day
that will be the whole 36kW and a bit. *I'm no expert (I merely suffer
these things in computer rooms) but I wouldn't be at all surprised to
find it eats another 18kW.

Seems to me that may exceed your power limit.

Splitting this lot evenly over three phases isn't going to be possible.
* Some of the time you'll have load on one of the phases only, sometimes
two, and only occasionally all three.

Andy.

It depends on the Coefficient Of Performance of the AC system.
Typically three. (Varies with outside air temperature.)
So.that's about 11 Kw split between three phases, equals 3.6Kw/phase
is about 15 amps per phase. More or less.

On Apr 13, 10:36*pm, "ARWadsworth"
wrote:
geoff wrote:
In message , ARWadsworth
writes
Arfa Daily wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq
ft units, one of which will be ours. The electrical supply comes
into the unit that will not be ours, so the landlord is putting a
new supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter,
and one of the questions on the application form refers to the type
of meter required. The two three phase options given are "Three
Phase Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? *I have checked with the
landlord to make sure that it is a three phase supply that he is
bringing over to our unit, and he says that we will "need a three
phase meter for a 40kVA supply" First question then. If each phase
is currently fused at 100A, does that mean that the incoming supply
is 25kVA per phase i.e. 75kVA, and that by dividing it between the
two newly created premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating
up together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will
be moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the
*potential* for everything being on together, does that mean that
the supply he is proposing giving us, is going to be adequate for
our needs ? Another question on the form is "Voltage - please delete"
The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A
fuses on a 3 phase supply does not give you 300A of available power
for 230V appliances (no matter how well you share the load between
the fuses) as the neutral is only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the
nominal voltage between phases) by the 100A fuse. ISTR that it
should be multiplied by sq rt of 3 to get the maximum power.

With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

You forgot Harry ...

No, I didn't.

And I was wrong. I offered my apologies to Harry. What more can you do? I
was wrong and I admitted it.

I will not try to make excuses, I will eat humble pie.

--
Adam- Hide quoted text -

- Show quoted text -

We all still love you :-)

On Apr 13, 11:49*pm, Andy Wade wrote:
On 13/04/2011 17:43, Owain wrote:

I suspect that at 3 x 100A you'd use Whole Current metering unless
there's a good reason not to.

Surely it's the supplier's or metering company's decision what type of
metering to install? *(Consumer chooses tariff, supplier installs
appropriate metering equipment of their choice.)

Round here (the old Eastern region) they tend to use whole-current
metering up to 3 x 200 A and CTs for larger. *If you find CTs on smaller
supplies it's generally where old meter equipment hasn't been updated.

--
Andy
The supply company needs an estimation of the electrical load.

"The Wanderer" wrote in message
...
On Wed, 13 Apr 2011 17:20:06 +0100, Arfa Daily wrote:

More or less definitive answer coming up......


We are in the process of taking some modern commercial premises, in which
the landlord is dividing down a 2k sq ft unit into two 1k sq ft units,
one
of which will be ours. The electrical supply comes into the unit that
will
not be ours, so the landlord is putting a new supply into our bit for us
as
part of the deal. The currently installed supply is three phase, with
each
phase company-fused at 100A, as far as I can see. We have approached
NPower
for a meter, and one of the questions on the application form refers to
the
type of meter required. The two three phase options given are "Three
Phase
Whole Current" and "Three Phase CT".

Right, 3 x 100a supply equates to a nominal maximum capacity of 75 kva.
First thing, you need to do is determine your maximum demand allowing for
diversity. Will everything be on and working at once? Do the fryers cycle
because of thermostats. I'm guessing you're probably going to be looking
an
MD of about 40-50 kva.

Whole current means the installation is connected directly through the
meter. A three phase WC meter will have a maximum capacity of about 80 to
100 amps per phase.

If you were going for some major industrial process with motors, heating
welding and all sorts of other equipment you could be looking at a demand
well in excess of 100a per phase. These meters operate using CTs (current
transformers), usually 200/5 or 400/5, so the meter is actually taking
only
a small percentage of the full load current. The incoming cable and main
fuses are also much larger.

I have not the slightest idea what the difference between these is, or
which
it will be that we need ??

See above


OK. All understood. That form has now been filled out and faxed to our
liason guy at NPower.



I have checked with the landlord to make sure
that it is a three phase supply that he is bringing over to our unit, and
he
says that we will "need a three phase meter for a 40kVA supply" First
question then. If each phase is currently fused at 100A, does that mean
that
the incoming supply is 25kVA per phase i.e. 75kVA, and that by dividing
it
between the two newly created premises, that is how he arrives at 40kVA ?

Is this a completely new supply or is he extending the installation to
give
you a sub-main off the existing installation? If that's the case, you'll
be
paying the landlord through a private meter, nothing to do with the
distribution company.


It is a new supply. The landlord has sent us a copy of the letter from EON
regarding them putting it in. In that letter, they request that a meter
supplier is appointed. However, that said, as he has told us that it will be
a 40 kVA supply, I have to assume that EON will be re-working the existing
75 kVA supply into 2 x 40 kVA supplies, one being for us, and one to serve
the remaining 1k sq ft unit that is still to be let. Does that make sense ?



Our demand will be fairly high. There will be two electrical fryers, each
loading at 2 x 9kW, so I guess if they are all on and heating up
together,
that would be a demand of 36kW. There is also a ceiling mounted airco /
heater unit that I don't know the specs for . It's not very big - maybe 2
ft
square. Other than that, the demand will be moderately low - some fume
extraction which is only a few amps, a couple of small fridges and
freezers,
lights (not more than 1kW) and small odds and sods for a normal ring
main.
So, given the *potential* for everything being on together, does that
mean
that the supply he is proposing giving us, is going to be adequate for
our
needs ?



I have now revisited this, and enquired with my daughter as to why she chose
fryer units with such a large power demand. It turns out that it was, to
some extent, an 'arbitrary' decision, based on the fact that the particular
model in question seemed to be the best value for money, whilst fulfilling
our performance needs. She had not considered the potential for two of these
gobbling up all of our incoming electricity supply capacity.

We have now found another model from the same manufacturer and range, which
is 2 x 6 kW per unit. This is capable of a 17 kilo per hour throughput of
frozen chips, so we think that two of these will be plenty adequate for the
busy nights. So, with those both on, there is the potential for a 24 kW draw
worst case, both thermostats on together. Now, a slightly different
question arises. According to the specs, this unit can be configured for
single phase or two phase operation. What would be the story there ? Would
it be both 6 kW elements paralleled up for single phase, and one element on
each of two phases for a two phase configuration ? Given the knowledge of
what supply we are going to have, which would be the preferred way of
hooking them up - all factors such as cost of fittings, cable, labour,
practicality for supply loading etc, considered ?

Arfa

On Thu, 14 Apr 2011 16:31:05 +0100, Arfa Daily wrote:

"The Wanderer" wrote in message
...


OK. All understood. That form has now been filled out and faxed to our
liason guy at NPower.

snip

Is this a completely new supply or is he extending the installation to
give
you a sub-main off the existing installation? If that's the case, you'll
be
paying the landlord through a private meter, nothing to do with the
distribution company.


It is a new supply.

OK, that's a new supply to you.

The landlord has sent us a copy of the letter from EON
regarding them putting it in. In that letter, they request that a meter
supplier is appointed. However, that said, as he has told us that it will be
a 40 kVA supply, I have to assume that EON will be re-working the existing
75 kVA supply into 2 x 40 kVA supplies, one being for us, and one to serve
the remaining 1k sq ft unit that is still to be let. Does that make sense ?

I guess the Landlord has told EON to install a 40kva supply, based on what
you've said to him[1]. I think you mentioned in your OP that there was
already a supply into the original unit and that it was located in the part
that wasn't in your tenancy. I would expect that to be left in situ to
supply the other half of the building. (Gentle) questions I'd be putting to
the LL, is the existing supply remaining for the other half of the
building, and has he merely asked for a 40kva supply based on your
estimates to him? (You can tell him you just want to be clear about the
arrangements.)

The distribution compan need a reasonable estimate of maximum demand for
any commercial or industrial premises to ensure they are installing the
correct cable and equipment to meet that demand. They will install a supply
with a nominal maximum capacity of 75kva, even if you only need 40kva.
(Single phase will only give a nominal MD of 25 kva, no use to you).

snip

I have now revisited this, and enquired with my daughter as to why she chose
fryer units with such a large power demand. It turns out that it was, to
some extent, an 'arbitrary' decision, based on the fact that the particular
model in question seemed to be the best value for money, whilst fulfilling
our performance needs. She had not considered the potential for two of these
gobbling up all of our incoming electricity supply capacity.

Unlikely, you finish up with more capacity through the cable and meter than
you will need.

We have now found another model from the same manufacturer and range, which
is 2 x 6 kW per unit. This is capable of a 17 kilo per hour throughput of
frozen chips, so we think that two of these will be plenty adequate for the
busy nights. So, with those both on, there is the potential for a 24 kW draw
worst case, both thermostats on together. Now, a slightly different
question arises. According to the specs, this unit can be configured for
single phase or two phase operation. What would be the story there ? Would
it be both 6 kW elements paralleled up for single phase, and one element on
each of two phases for a two phase configuration ? Given the knowledge of
what supply we are going to have, which would be the preferred way of
hooking them up - all factors such as cost of fittings, cable, labour,
practicality for supply loading etc, considered ?

If it were me, I'd go for the 9kw models as long as they can be connected
across three phases, 3kw per phase. You should aim to keep your load
reasonably well balanced across the three phases.

[1] It's a while since I had anything to to do with commercial/industrial
tariffs, but your LL might be doing you a favour. From memory anything over
a nominal 50kva supply will only be metered on a maximum demand tariff.
Below 50kvz you have the choice of straight kwh or maximum demand.[2]

[2] An MD tariff is most beneficial to a customer with a very high load
factor, i.e. he is running continuous processes that are drawing a steady
kwh demand more or less continuously. If you have a process that ticks over
at a nominal demand of 30kva but for 5 minutes in every hour kicks up to
200kva, you will be penalised because the supply company has needed to
install much larger cables that are really only needed for just 5 minutes
in every hour. Bit of an over-simplification but I hope that makes sense.



--
The Wanderer

There is no place like 127.0.0.1

On 14/04/2011 16:05, harry wrote:
On Apr 13, 10:36 pm,
wrote:
wrote:
In , ARWadsworth
writes
Arfa wrote:
We are in the process of taking some modern commercial premises, in
which the landlord is dividing down a 2k sq ft unit into two 1k sq
ft units, one of which will be ours. The electrical supply comes
into the unit that will not be ours, so the landlord is putting a
new supply into our bit for us as part of the deal. The currently
installed supply is three phase, with each phase company-fused at
100A, as far as I can see. We have approached NPower for a meter,
and one of the questions on the application form refers to the type
of meter required. The two three phase options given are "Three
Phase Whole Current" and "Three Phase CT".
I have not the slightest idea what the difference between these is,
or which it will be that we need ?? I have checked with the
landlord to make sure that it is a three phase supply that he is
bringing over to our unit, and he says that we will "need a three
phase meter for a 40kVA supply" First question then. If each phase
is currently fused at 100A, does that mean that the incoming supply
is 25kVA per phase i.e. 75kVA, and that by dividing it between the
two newly created premises, that is how he arrives at 40kVA ?
Our demand will be fairly high. There will be two electrical fryers,
each loading at 2 x 9kW, so I guess if they are all on and heating
up together, that would be a demand of 36kW. There is also a ceiling
mounted airco / heater unit that I don't know the specs for . It's
not very big - maybe 2 ft square. Other than that, the demand will
be moderately low - some fume extraction which is only a few amps, a
couple of small fridges and freezers, lights (not more than 1kW) and
small odds and sods for a normal ring main. So, given the
*potential* for everything being on together, does that mean that
the supply he is proposing giving us, is going to be adequate for
our needs ? Another question on the form is "Voltage - please delete"
The three
options given are 415V 11kV and 33kV. I assume that the correct
answer there is 415V as it's a three phase supply direct into the
premises ?

Have you got 3 phase appliances? It is worth noting that 3x100A
fuses on a 3 phase supply does not give you 300A of available power
for 230V appliances (no matter how well you share the load between
the fuses) as the neutral is only rated at 100A.

I have not done 3 phase for a while (other than just connect up a few
machines) but 40kVA sounds like he has just multiplied 400 (the
nominal voltage between phases) by the 100A fuse. ISTR that it
should be multiplied by sq rt of 3 to get the maximum power.

With a bit of (bad) luck Dennis should be along shortly to explain
everything as he is a f***ing know all.

You forgot Harry ...

No, I didn't.

And I was wrong. I offered my apologies to Harry. What more can you do? I
was wrong and I admitted it.

I will not try to make excuses, I will eat humble pie.

--
Adam- Hide quoted text -

- Show quoted text -

We all still love you :-)

But only in a manly, viking way....


--
Dave - The Medway Handyman www.medwayhandyman.co.uk

The Medway Handyman wrote:
On 14/04/2011 16:05, harry wrote:

We all still love you :-)

But only in a manly, viking way....



like this

http://www.rathergood.com/gaybar

In article ,
says...
I've got a 10kW shower in my bathroom. It's definately not three-
phase.

Its not going to be on for hours at a time.

Ah - you've not got teenagers then.

--
Skipweasel - never knowingly understood.

Arfa Daily wrote:

We have now found another model from the same manufacturer and range,
which is 2 x 6 kW per unit. This is capable of a 17 kilo per hour
throughput of frozen chips, so we think that two of these will be
plenty adequate for the busy nights. So, with those both on, there is
the potential for a 24 kW draw worst case, both thermostats on
together. Now, a slightly different question arises. According to
the specs, this unit can be configured for single phase or two phase
operation. What would be the story there ? Would it be both 6 kW
elements paralleled up for single phase, and one element on each of
two phases for a two phase configuration ? Given the knowledge of
what supply we are going to have, which would be the preferred way of
hooking them up - all factors such as cost of fittings, cable,
labour, practicality for supply loading etc, considered ?

Many normal household hobs come with wiring diagrams for 1, 2 and 3 phase
supplies. When using the single phase option then all the live terminal are
linked together at the hob.

The use of a single phase would need you to balance the other two phases
with other appliances.

--
Adam