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!