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.
I am trying to find a website that has a list of typical currents
drawn by, or VA rating (not Watts - I don't know the appliance power
factors) of, different domestic appliances so that I can calculate if
I would exceed the 100A limit of a single phase supply. Anyone know of
such a website?
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.
Thanks for your help.
Are you having all electric space and water heating and cooking ? You
might then exceed the 24kW that the supply will feed you. Otherwise I
doubt you can come close to needing it. Many UK supplies are limited at
Are you intending to build a workshop with heavy machinery ? Are you going
for a fully electric heating, cooking, automation systems etc. etc. ?
If you come close to needing a three phase supply for an ordinary 5 bedroom
house without any specific installations that would use it, then you'll also
be coming close to bankruptcy with bills you'll receive on using that amount
Using triple phase and neutral supplies is typically used for industrial or
excessively heavy domestic installation, i.e. letting out separate
apartments, heavy workshop machinery attached to the house etc. etc. So
anyone using such a supply is normally making money out of it to justify the
A simple test to carry out, is to wonder around the house and total up the
load of all the electrical equipment you have plugged in to the mains
supply. i.e. heating, lighting, cooking, laundry, food storage etc. etc.
and see how much power it would use if it was all running at the same time,
even all the little clock radios and things, and I think you'll be amazed at
how little it really does draw compared to the supply's capability.
I vaguely remember the woodyard I worked at having to pay three figure
numbers for the upgrade. Up to then he was running everything on a
The genny would be viable if you had a means of abstracting the heat.
(Think how much oil a CH boiler uses to no other effect but heating,
while a generator not only burns the same fuel but supplies the lecky
too, also, as well.)
A good ex-military genny would be cheaper than a tranformer on a stick
in your garden. And you could use it to annoy the neighbours if they
upset you -or even if they haven't (yet.)
How much oil does a central heater use? And what generators have a
comparable fuel consumption? And how much would heat exchangers for
the cooling and exhaust cost?
Got a link to that in the Corris site anyone?
Anyone know if you can use old lubricating oil in a diesel? I know
that you can use it to spray a jet from an oil-pump onto a firebrick
alongside a fan that would work as a blowlamp for melting aluminium
(Yes I know this is getting silly but I didn't start the thread.)
The internal combusition engine's biggest product is heat. Far more heat
than power is produced. Extracting "all" the heat, and it produces a hell
of a lot, and power (electiucty) it is very efficient. But most people would
not use all the heat and power available, so they are very inefficient.
Heat exchangers are not cheap. Many people make their own. It is using
all the heat available. Having a small LPG genny, about 1.5 kW/hr, and
extracting all the heat is feabile. But you have to extract all of its heat
and store it in a large thermal store. Then your house has to be run mainly
on LV lights, run from batteries overnight with the genny off, and all
appliances run on gas (gas fridges are available). Washing machines, etc,
have to be super energy efficient and hot and cold fill, with the hot water
comming from the stored water. No appliance should draw more than 1.5 kW.
Now there are Combined Heat and Power Stirling units available.
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Excellent sites well the first one was excellent except that it gave
no clear idea of the size weight and price. Ditto the other one but I
couldn't get on with the way the pictures loaded.
I'd never heard of the stirling engine and am having difficulty with
the concept. They seem to be shooting themselves with the overbuild
quality as a fuel efficient small unit that wears out rapidly would
sell if it was cheap enough to supply a site. It could be without the
heat saving ad ons.
Of course the firms shown were designing a unit for specific purposes
not including what I would buy one for. If I was in the market for a
I wonder why they can't incorporate an oil way in the crancks and etc
the way that motorcycle 2 strokes do.
It's Sunday evening. Mum's doing the washing/drying/ironing, Dad's cooking
lunch and four teenage children are showering/doing homework/watching TV.
(Putting aside the debate about stereotypical representations) I think that
this family could draw the following loads simultaneously:
12.5A (Washing machine)
14.5A (Tumble dryer)
10A (Cooker (electric))
6A (Microwave oven)
8A (Electric kettle)
2A (Hi-Fi Stereo, surround sound system.)
2A (2 x Computer)
1A (2 x 17" monitor)
6A (Hair dryer)
0.5A (17" monitor)
2A (Shower pump)
2A (Extractor fan)
12.5A (Immersion or water heater)
3.5A (Central heating pump)
3A (Fan Heater 1/3hp)
5A (Sundry electrical loads)
That's a total 124.5 amps. OK, we can argue that their approach to energy
efficiency could be improved. In terms of rating a supply, however, a single
phase 100A supply seems inadequate.
How do my load estimations look?
Bog standard incandescent - 3 * 3 * 60W reflectors - the room is about 18
foot by 7 foot, switched in a bank of 3, and a bank of 6 - if you knock
the bank of 6 on first of a night it can take several seconds before your
eyes recover, and it sure as hell wakes you up :-p
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Only for the small proportion of time it's heating water; "modern" machines
use little water compared to older ones. And few have elements above 2kW.
So a better figure for the peak draw would be 9A; and with some 15% of the
time spent heating, rather than spinning, tumbling, etc., the average figure
will be more like 3A.
Not as high as that, but could be 12A, and unlike the washing machine will
be sustained for a longer time - 60-90 minutes.
Yes, but again there's a thermostat. If Mum's ironing her linen tablecloth
with the steam going full on, you might see an 80% duty cycle; if she's
just passing it over her Janet Regier with the iron set a bit under the
one-dot position, it'll be a 5-10% duty cycle...
Unlikely to be that high for either, and again will be smoothed by thermostat
Same comment as washing machine: heating and drying account for say 50% of
the duty cycle, the rest is spent spraying the already-hot water round the
washdosh and rinsing its contents with cold water; so average down to 5-6A.
Yes, maybe that high if we've got all 4 plates on the go and something in
the oven (each plate 2kW and maybe 1kW oven, but thermostats clicking in
and about bring the average down near the figure you suggest).
Ooh, that's a big one, as the bishop said to... but seriously, most MWs
are in the 600W-800W range, so 3A rather than the 1.5kW which 6A would mean.
And is Dad cooking for real (on the cooker), or just heating something up
(microwave)? Shirley he's not using both?
Yes, while it's on; but not for more than 4-5 minutes in an hour.
Hang on. If Dad's cooking, Mum's ironing, and the kids are doing homework
on the three computers you've enumerated *and* watching teli *and* got the
Hi-Fi on the go, who's left to wash the hair?
Hmm, it's the cat in the shower?
What, immersion *and* CH on the go at once? And there's a 'stat on the
immersion; and that's a monster CH pump - steady-run current will be well
Possible but profligate!
They're notably pessimistic; but they do show why (a) new builds usually
have a 100A mainfuse these days, rather than the 60A which used to be
standard; (b) illustrate why the main incomer is a cartridge fuse rather than
an MCB (well, there's cost reasons too, and the vulnerability of an MCB to
kids turning them off if they're in an outdoor-accessible meter cupboard).
(The wired fuse allows getting on for twice the nominal rating to be drawn
for a good few minutes before it blows, though it'll rupture within
milliseconds with a serious short circuit.) In particular, lots of the
loads you mention are thermostatically controlled, and you list the
peak rather than the average. The heating effects in the circuit cables
(from meter tails down to final circuits) take a while to kick in, so
in practice we don't see houses either blowing their main fuses or
melting/drooping PVC cables all over the place.
There's also a difference between a single-family house - the case you've
suggested here - and "houses in multiple occupation", i.e. converted into
flats/bedsits. For a bedsit conversion, it's more likely that there'll
be multipe fanheaters/hairdryers/kettles and all sorts going on at once
- in the evening as the occupants come home, say - and Good Practice says
you apply lower "diversity" factors (that's RegSpeak for "not all the
possible loads will be on at once") in such a case, or in a school domestic
science "lab" where all cookers/oven/baby-Bellings *will* be on at once,
than for a domestic installation.
On 26 Sep 2003 13:05:59 GMT, firstname.lastname@example.org wrote:
uWaves have RF outputs in the 600 to 800W range but aren't that
effcient at converting electrickery into RF. 1.5kW for an "800W" uWave
isn't too far from the mark.
You mention the regs and diversity, calculating that correctly is what
is important rather than simply adding up all the possible loads. TBH
you can probably ignore most things that are not "heaters" as they
won't take that much power, allow a few kW for them. It's the biggies
like water heaters (from washing machines, through kettles and
immersions to showers) and space heating that really determine the
Dave. pam is missing e-mail
Thanks, Stefek, this was most helpful.
I went round the house and switched various loads on and off. I
measured the "with load" and "without load" current through the live
incomer using a Fluke clamp meter. I recorded the following readings
(difference between "with" and "without"):
Tumble dryer = 11.9A average, 16.0A peak
Dishwasher = 13.6A for at least 10 mins
Electric cooker (two ovens on full, no rings on) = 18.7A
Electric cooker (four rings on full, no ovens on) = 25.3A
Microwave oven (Cat D) = 7.0A
Electric kettle = 9.2A
Toaster (two slice) = 3.1A
Hair Dryer = 7.3A
All lights on (40 bulbs) = 11.6A
Electric fan heater on full = 11.6A
Washing machine = [still to test]
The point of my original post was not how expensive or inefficient it
would be to use all the above at the same time. It is that, worst
case, you could conceivably consume near the 100A single phase limit
with standard appliances.
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