Upgrade to a three phase domestic supply?

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On 28 Sep 2003 08:21:22 -0700, Pandora wrote:
<snip>

Yes, but you really do need to try and grasp the principle of diversity. If you switch every single appliance in your house on the same time, it is very likely that you would exceed the maximum design ratings of the supply equipment or the installation. But, and it's a very big but, that load *will* fall off as thermostats start to operate. Electrical cables and mains fuses are more than capable of withstanding overloads (as distinct from faults) for short periods of time, although the installation fuses or mcb's may operate.
It might surprise you to learn that the after-diversity maximum demand per dwelling on a non-electric heating estate of say 50 houses for design purposes could be a low as 1.5 to 2kva per dwelling, although each dwelling could have some 15 to 20kva of load installed! The mains distribution equipment installed will have a notional maximum load of 75 to 100 kva, not 750 to 1,000kva.
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OK. After some reflection, I'll stay with a single phase supply.
Thanks to all posters.
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You're welcome; and thanks in turn for not taking umbrage at the relatively robust terms in which your knowledge was supplemented ;-)
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Good idea
--
geoff

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Well high. You make no allowance for diversity. Many of the ratings quoted are well above the currents actually likely to be drawn. Also, they are peak currents. Most will only draw these for short periods, which are unlikely to be exactly coincident in time. Also, short transient currents above the rating are permitted. It is only if the current remains over the rated current for a long time (i.e. minutes) will it matter.

Only whilst heating water, which might be for ten minutes at a time. Average current much lower.

Again, average current is lower. The rating you give is actually above the 13A fuse, so is too high.

Low duty cycle. Mine only comes on for a few seconds before cutting out for a minute. Average current much lower.

Again, low duty cycle. The compressor only comes on occasionally.

I don't believe a freezer would draw 3A on average.

Only whilst heating, which isn't very much.

If cooking a complex dinner, the average might exceed this.

Only for a couple of minutes.

Only for a couple of minutes.

Hope you don't have neighbours. That would produce about 125W rms per channel on a 50% efficient amplifier, which would blow your ears off, unless you wear baseball caps backwards.

Well over. The power supply is its maximum rating. It will only draw a fraction.

Probably about right.

Only used for a couple of minutes at a time.

Only used for a couple of minutes at a time.

Only used for a couple of minutes at a time. This rating will produce a hurricane.

Should only be used for backup. You do have central heating that heats the water? It is also thermostatically controlled, so isn't a constant load.

This is totally way over the top. Normally, the entire central heating system is fused at 3A.

That's a very little heater. However, it could be a reasonable average in a centrally heated home with thermostatic control.

Does this include floodlighting the football pitch? I have about 10 bulbs, with an average wattage of around 15W, giving 150W ~= 0.6A. Even if you have tonnes of halogen lighting, I'd be surprised to see a figure this high. This is 2.4kW of bulbs, or 24 100W bulbs, all on simultaneously.

single
This would absolutely covered by diversity calculations. You could probably squeeze it into a 60A supply. Remember, it doesn't matter if the instantaneous current exceeds 100A for a short period. It is the average current drawn over a period of minutes that counts. I doubt that these loads in actual use (rather than pathological timing) would actually exceed 60A).
Christian.
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It looks like a bit of time budgeting might be in order
--
geoff

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You seem to think that people have at least 4 hands each and do in fact do 2 3 or 4 things at once. Others have commented on diversity.

1kW is more likely.

2-4A
not many eating 360w nowadays.

try 65-150w

may be much higher

more likely 12 or 13A

try 20-50w

may be higher

thats more like a paint melting gun

500w?? no, closer to a tenth that

more ike 20 or 30w than 500

divide that by 10. When the house is eating 100A theres no way the CH will be on :)

as well as cookers and all the other loads? 240v 100A is already 24kW.

IRL you'd cook before exceeding a 100A house supply. Lots of places still run happily on 40A supplies.
Regards, NT
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On Fri, 26 Sep 2003 01:55:27 UTC, "BigWallop"

Perhaps he has a wife and seven daughters who all have ensuite showers and want to use them at the same time.... :-)
--
Bob Eager
rde at tavi.co.uk
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Pandora wrote:

Would seem like overkill? If not electric heating would not 230 volt 100 amps be OK; unless it's a boarding house with people living, cooking/eating etc. in individual rooms? Reminds one of the old 'shilling in the slot meter' old old digs! Our four bedroom insulated wood frame 1530 sq. ft (main floor) plus full basement has the here standard 200 amp 115/230 volt supply. Wired over head from a pole mounted distribution transformer about 120 metres away. In this somewhat colder and longer heating season than the UK; we have electric baseboard heating with individual thermostats for each room/area. Thirty five gallon hot water heating tank, clothes dryer, dish washer, radios, TV, computers etc. Several other (about five IIRC) typical homes are supplied from the same distribution transformer. No voltage problems. Lights and wall plugs are 115 volt, 'heavy' items, viz. cooking stove (oven +4 hobs), water heater, electric heating is 230 volt. Basement workshop is mixture of 115, and 230 volt for occasional heater and bench saw. On a 24 hour average, cos never is everything 'ON' at once, the consumption is around 4-5 kilowatts per hour, often less. At a maximum, even if one comes home turns up the heat and put clothes on to wash, maybe boils the kettle for a few minutes etc. etc. I doubt if it ever goes up to the 'rated' maximum which in our case is 200 amps X 230 volts = 46,000 watts or 46 kilowatts! Suggestion.
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"Pandora" wrote | I have moved to an old 5 bedroom house that I plan to renovate, | including a complete rewire. | This is also an opportunity to change the domestic supply from 100A | single phase to three phase, if I wish. | Aside from the danger of 415V in the house, would anyone care to | comment on the risk/reward of a domestic three phase supply? (E.g. | higher standing charge?). I do not intend to use any three phase | equipment in the house.
About the only requirement for 3 phase (as others have subsequently illustrated with their demand calculations) in a single family household is if there is a high storage space heating and storage hot water load, as all these would come on simulataneously during the off-peak time and there is no diversity applicable.
In a house which is subdivided into bedsits etc, or used as B&B with lots of electric instantaneous showers, or if you run a pottery kiln etc, then things are different.
Owain
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We have 3 phase already in our chapel - being converted to house and workshop. I am keeping it as I am a woodworker and have some 3 phase machines - and future machines bought will be much cheaper if 3 phase, second hand that is, not much difference in new prices. Also, having a large workshop I could for instance accomodate a potter with a large kiln which would definitely need 3 phase. Except for these considerations 3 phase is unecessary and no normal domestic set-up is ever likely to exceed 100amps. However the problem remains - what considerations are there with respect to re-wiring in 3 phase. I'm ok with single phase wiring and I know about spreading the load between phases but are there any particular problems or no-nos, or good sources of info?
cheers
Jacob
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snipped-for-privacy@pandora.be (Pandora) wrote in message

I looked at doing this but one of the things the supplier insists on is that all phases have the same loading. To do this meant spliting the phases around the house which i thought was too dangerous so ended up with a uprated supply 100amp i think , this was the largest they do at the base price any larger and it was a special job = expensive. Rob
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