One for the electrical boys, please ...

[Owain]

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

Owain

[Owain]

Much of the heat of the fryers should go up the exhaust fans.

Which does mean there'll be a lot of replacement air coming into the building from outside, though.

Owain

[Arfa Daily]

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

[Mike Tomlinson]

In article , Arfa Daily writes

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.

[The Medway Handyman]

Is that 9kW including VAT or plus VAT?

[dennis]

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.

[dennis]

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.

[The Wanderer]

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

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.

See above

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.

415 volts, but see above.

[docholliday]

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.

[John Williamson]

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.

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

Tciao for Now!

John.

[Andy Wade]

Correct.

[Arfa Daily]

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

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 ?

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

[Huge]

That's a serious chip dependency you have there.

But seriously, what is this business? I can't see a chip shop in an industrial unit ...

[The Wanderer]

OK, that's a new supply to you.

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).

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

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.

[Skipweasel]

Ah - you've not got teenagers then.

[ARWadsworth]

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.

[hugh]

In message , "dennis@home" writes

[Owain]

According to

average portion weight of chips is 13oz. / 367gm. and the average portion weight of fish is 8oz. / 226gm. The smallest portion of chips weighed 8oz. and the largest portion a whopping 21oz.

So working with an average of 367 gm per portion your fryer will do 40 portions an hour. Or 20 portions in half an hour, or 10 portions in 15 minutes. This is without taking into account product cooking times or cooling/filtration cycles. You can assume any manufacturer's throughput figures are optimistic.

Unless you want people waiting for 20+ minutes for chips, you'd have to hope not many orders come in simultaneously. If this is for home delivery, take into account TV commercial breaks / sports match half- times as you may have significant peaks throughout service.

Owain

[Arfa Daily]

Good point, but I don't think that we entered into any specifics about what our demand would be on any supply, before he told us that it would be a 40 kVA supply that EON would be putting in.

OK. Mostly understood, I think. However, as each of those fryers has 2 x 9 kW of heating elements, would that not equate to 6 kW per phase for each fryer i.e. a total of 12 kW per phase when both fryers are in use, and happen to both be 'statted on at the same time ? Do the three demands then just add up to amount to a grand total of 36 kW ? If so, then that seems to be coming pretty close to the system capacity of 40 kVA (am I right in thinking that for resistive loads kW = kVA ??)

Arfa

[Arfa Daily]

Not all 'units' are *industrial* units, and not all places that serve chips, are 'chip shops' ... !!

It is a retail unit, in a terrace of other retail units, and we will be selling mainly American-style char-grilled burgers. Sort of 'quality' junk food, if you like ... :-)

Arfa