Hi all

OK so I'm obviously being majorly dumb here, but I am still struggling with
this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch technical
specs publication I get the following figures:
(note that where alternatives are stated, these are values for different
models)

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000

It would surprise me greatly if the average family doesn't regularly have
all this stuff running at the same time at some time during a normal week.
But that lot adds up to 10320watts - 43A on a 32A ring.
So where does the diversity bit come in?

I am considering a single oven, designed to run off a 13A supply, but if I
add that to the above load it looks like meltdown city!

So, can I take a fused spur off my cooker feed to reduce the ring load or is
this not necessary

TIA

Phil

On Jun 7, 12:29*pm, "TheScullster" wrote:
Hi all

OK so I'm obviously being majorly dumb here, but I am still struggling with
this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch technical
specs publication I get the following figures:
(note that where alternatives are stated, these are values for different
models)

Dishwasher 1900 or 2500

Only when heating water. I doubt it uses 250W the rest of the time....

Microwave 1220 or 1900
Washing machine 2300

Only when heating water. It will draw under a kW on spin.

Condensing Dryer 1.9kWhr (is this the same as 1900w?)
I'd be surprised if that was drawing peak power continuously. Surely
it only heats at intervals.

TheScullster wrote:
Hi all

OK so I'm obviously being majorly dumb here, but I am still struggling with
this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch technical
specs publication I get the following figures:
(note that where alternatives are stated, these are values for different
models)

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000

It would surprise me greatly if the average family doesn't regularly have
all this stuff running at the same time at some time during a normal week.
But that lot adds up to 10320watts - 43A on a 32A ring.
So where does the diversity bit come in?

Iys highly unusual to be boiling a kettle, running a microwave on full
power and a washing machine on hot wash heating cycle and a condensing
dryer on full dry cycle all at teh same time. But yes, if you do, you
will trip the MCB.

Remember many houses are fused at the supply at 60A total. Whole house.

we get rather close to that these days.



I am considering a single oven, designed to run off a 13A supply, but if I
add that to the above load it looks like meltdown city!


Again ovens are cyclical - on-off.

If you had 50A running in the kitchen for any length of time, that's
about enough heat to heat a fairly large house., Ive got 4000 sq ft and
that's what it takes to heat the whole shebang in winter with -5C and a
gale..

So basically, those loads are peak loads., Not continuous loads, yes,
you might by dint of turning it all on at once get an overload, but the
fact that by and large most people don't, is proof that the diversity
thing works.

If it bothers you, run another ring.


So, can I take a fused spur off my cooker feed to reduce the ring load or is
this not necessary


I'd do that for an oven, yes.


TIA

Phil

On Mon, 7 Jun 2010 12:29:35 +0100 someone who may be "TheScullster"
wrote this:-

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000

It would surprise me greatly if the average family doesn't regularly have
all this stuff running at the same time at some time during a normal week.
But that lot adds up to 10320watts - 43A on a 32A ring.
So where does the diversity bit come in?

They may at times have this all stuff running at the same time,
though probably not that regularly.

The question is then, how long for? The heating elements in the
dishwasher, washing machine and drier are not on all the time. They
will cycle on and off as determined by the programmer and
conditions. The element in the drier may be on for long periods, the
elements in the other two are unlikely to be on for more than five
minutes at a time.

The kettle is on for not long while it boils, a few minutes even if
full.

So even if all these heating elements happen to be on at the same
time, how long does it last? Five minutes or so. During this time
the wires will become hotter than they would be otherwise, but they
can then cool down when the current reduces ready for the next
surge.

From the curves a 32A MCB might operate in something like 4,000
seconds if a current of 43A passes through it continuously. 66
minutes. As a rule of thumb a "normal" wiring system can tolerate
twice the maximum designed current for an hour before it becomes
dangerously overheated (don't try this at home children). Some
highly engineered systems are not capable of this and will suffer
runaway temperature rises, but house wiring systems are not highly
engineered.

I am considering a single oven, designed to run off a 13A supply, but if I
add that to the above load it looks like meltdown city!

So, can I take a fused spur off my cooker feed to reduce the ring load or is
this not necessary

Assuming the cooker switch is within 2m of the oven I would run a
suitable cable to a fused connection unit and from there run a
suitable cable to the oven. Where the first cable starts depends on
the precise arrangement, but that cable will be at least 4 square
millimetres in size.

That assumes that the existing cooker circuit is adequately sized
for the cooker and the oven. There are simple formulae to calculate
the diversity for a cookers in a domestic setting.

If neither of these conditions is true then I would look at wiring
it to the ring circuit, or if that was not possible due to diversity
calculations I would consider a new radial circuit to the oven.




--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

"David Hansen" wrote

Assuming the cooker switch is within 2m of the oven I would run a
suitable cable to a fused connection unit and from there run a
suitable cable to the oven. Where the first cable starts depends on
the precise arrangement, but that cable will be at least 4 square
millimetres in size.

That assumes that the existing cooker circuit is adequately sized
for the cooker and the oven. There are simple formulae to calculate
the diversity for a cookers in a domestic setting.

Thanks Dave

I currently have a 6mm feed to the existing separate double oven and hob.
The hob in the proposed new layout will be within 2m of the existing switch,
so I intended to use the same feed for this.
The new oven will be located on the opposite wall, so I was considering
putting a joint box in the supply cable (located in the loft above) and
dropping down to a second supply point near the new oven.
Should this be a second "cooker point", or a fused spur rated for the 32A
upstream condition?

Phil

On Mon, 7 Jun 2010 13:39:06 +0100 someone who may be "TheScullster"
wrote this:-

I currently have a 6mm feed to the existing separate double oven and hob.
The hob in the proposed new layout will be within 2m of the existing switch,
so I intended to use the same feed for this.

That is fine.

The new oven will be located on the opposite wall, so I was considering
putting a joint box in the supply cable (located in the loft above) and
dropping down to a second supply point near the new oven.
Should this be a second "cooker point", or a fused spur rated for the 32A
upstream condition?

Not having seen the layout, for future flexibility I would put in a
cooker switch near the new oven
http://www.tlc-direct.co.uk/Products/MKK5205.html.

If the protective device for the cooker circuit is rated at 30/32A
then I might consider a smaller version
http://www.tlc-direct.co.uk/Products/MKK5105.html but getting
cables into this might be interesting.

Depending on the ability of the oven to deal with fault currents,
the manual may help with this, I might then add an unswitched fused
connection unit somewhere
http://www.tlc-direct.co.uk/Products/MKK0337.html.

If I wasn't too worried about future flexibility I might not bother
with the above and go for a switched fused connection unit
http://www.tlc-direct.co.uk/Products/MKK1040.html, having studied
its characteristics carefully. One of those is unlikely to be able
to break fault currents, but the protective device should break the
fault current before the switched fused connection unit bursts into
flames and it is unlikely someone will be able to operate the switch
before the protective device clears the fault.




--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

"TheScullster" wrote in message
. uk...

"David Hansen" wrote

Assuming the cooker switch is within 2m of the oven I would run a
suitable cable to a fused connection unit and from there run a
suitable cable to the oven. Where the first cable starts depends on
the precise arrangement, but that cable will be at least 4 square
millimetres in size.

That assumes that the existing cooker circuit is adequately sized
for the cooker and the oven. There are simple formulae to calculate
the diversity for a cookers in a domestic setting.

Thanks Dave

I currently have a 6mm feed to the existing separate double oven and hob.
The hob in the proposed new layout will be within 2m of the existing
switch, so I intended to use the same feed for this.
The new oven will be located on the opposite wall, so I was considering
putting a joint box in the supply cable (located in the loft above) and
dropping down to a second supply point near the new oven.
Should this be a second "cooker point", or a fused spur rated for the 32A
upstream condition?

Phil

Hi Phil

If possible it would be better to run a new 6mm from the cooker switch
connected to the input side of the switch to a new switch for the oven. From
the new oven switch run a 6mm to a 35mm deep back box and fit a fused spur
to connect to the oven. If at a later date you wanted to upgrade your oven
(single ovens are very poor) you can change the fused spur to a cooker
outlet plate.

Cheers

Adam

In article ,
TheScullster wrote:
OK so I'm obviously being majorly dumb here, but I am still struggling
with this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch
technical specs publication I get the following figures: (note that
where alternatives are stated, these are values for different models)

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000
Dishwasher, washing machine and possibly tumble drier all have thermostats
on their heating elements (which use the majority of the power) so would
run at an *average* well below the peak stated. Rather like an oven does.

Not sure about a microwave. Of all those only the kettle definitely takes
a (near) constant load while in use.

--
*I'm planning to be spontaneous tomorrow *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
TheScullster wrote:
OK so I'm obviously being majorly dumb here, but I am still struggling
with this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch
technical specs publication I get the following figures: (note that
where alternatives are stated, these are values for different models)

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000
Dishwasher, washing machine and possibly tumble drier all have thermostats
on their heating elements (which use the majority of the power) so would
run at an *average* well below the peak stated. Rather like an oven does.

Not sure about a microwave.

Pulsed on/off/ Difficult to modulate a magnetron. Expensive too, so
guess what..

"Dave Plowman (News)" wrote in message
...
In article ,
TheScullster wrote:
OK so I'm obviously being majorly dumb here, but I am still struggling
with this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch
technical specs publication I get the following figures: (note that
where alternatives are stated, these are values for different models)

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000
Dishwasher, washing machine and possibly tumble drier all have thermostats
on their heating elements (which use the majority of the power) so would
run at an *average* well below the peak stated. Rather like an oven does.

Not sure about a microwave. Of all those only the kettle definitely takes
a (near) constant load while in use.

--
*I'm planning to be spontaneous tomorrow *

Dave Plowman London SW

Due to being a lazy ******* I have my tumble drier, dishwasher and washine
machine on a 20A MCB (it is a ring but I need to change the MCB). I'll
change the MCB when it trips and not befo-)

Adam

On Jun 7, 12:29*pm, "TheScullster" wrote:
Hi all

OK so I'm obviously being majorly dumb here, but I am still struggling with
this diversity issue when applied to kitchen white goods!

Looking at the "connected power" figures (in watts) from a Bosch technical
specs publication I get the following figures:
(note that where alternatives are stated, these are values for different
models)

Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Condensing Dryer 1.9kWhr (is this the same as 1900w?)
Kettle 3000

It would surprise me greatly if the average family doesn't regularly have
all this stuff running at the same time at some time during a normal week..
But that lot adds up to 10320watts - 43A on a 32A ring.
So where does the diversity bit come in?

I am considering a single oven, designed to run off a 13A supply, but if I
add that to the above load it looks like meltdown city!

So, can I take a fused spur off my cooker feed to reduce the ring load or is
this not necessary

TIA

Phil


The 30 or 32A rating for ring circuits isn't their peak ampacity, but
rather the max continuous rating. Its quite normal to pull 45A or more
on a kitchen ring circuit at times, and neither the cable, fuse nor
MCB objects. A fair few kitchens contain enough appliances on one ring
to be able to consume much more if they were all running at full power
at one time.
Eg: 2.4kW oven, 3kW kettle, 3kW washing machine, 2kW dishwasher, 1.5kW
microwave, 3kW toaster and other small loads, 15kW in all.


NT

On Jun 7, 12:29*pm, "TheScullster" wrote:
Dishwasher 1900 or 2500
Microwave 1220 or 1900
Washing machine 2300
Kettle 3000

Not material.

Condensing Dryer 1.9kWhr (is this the same as 1900w?)

Material.

Vented dryers are worse, 3200W for 1.5-2hrs, although do cycle the
heater.

A 32A ring has some "overcurrent tolerance" designed in.
#1 Each ring leg must have a CCC of 20A.
#2 A ring should have load balanced across the legs.
#3 32A MCB/RCBO takes circa 20min to trip at 40A.

Now, whilst #2 may not always be true, #1 should be true by design.
Combined with #3 you have a reasonable margin of safety.

I would only be concerned with a Whole House Ring.
In that situation you may want to install a dedicated 20A radial to
the dryer, or break the existing ring so as to create a 32A kitchen
ring and 32A house ring. If the wiring is 4mm you could break it to
create two 32A radials - but this is very unlikely, 4mm is not often
found due to pre 17th EFLI limiting length and basic economics making
it pricey.

If wiring afresh I prefer a few 32A 4mm radial & 20A 2.5mm radials,
gives better redundancy & "survivability" with RCD/RCBO.