"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