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I'm planning to convert a house into flats. As part of the conversion I require increased supply of electricity.

  • The electrical utility supplier said they can't advise me on what I need but typically it's between 2-6kVA.
  • My builder says somewhere in the region of 15kW!! That's a massive difference.

Power Estimate

I understand my builders equations more but wanted to know if he's right:

  • Oven: 40 Amps
  • Lighting: 10 Amps
  • Other: 10 Amps

~60 Amp requirement

Watts = Amps * Voltage
Watts= 60 Amps * 240 Volts = 14400 Watts = 14.4kW

So to convert to kVA you would divide by PowerFactor.

Since power factor is between 0-1 - we can be conservative and assume it's 1.

Hence 14.4kW or 14.4kVA

Question

Is this correct? Are we overestimating things here? I'm not sure how a flat can have a consumption of 2kVA - surely this guy from the power team is missing the point here?

Can anyone help bridge the gap?

  • Where in the world are you? In the US at least, it's typical to talk about electricity supply in terms of current (Amps), rather than kW or kVA. Unfortunately, asking about a "typical" supply may be off-topic here, though, because it does depend on so much - age of the home, heat source, hot water source, etc. – mmathis Jan 18 '17 at 18:59
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    And, I think your math to convert kW to kVA is wrong - when you divide by a number between 0 and 1, you wind up with a bigger result. So 14.4 kVA is actually the lowest you would get (using a PF of 1); a PF of e.g., 50% would yield 28.8 kVA given 14.4 kW. – mmathis Jan 18 '17 at 19:02
  • You can't just armwave Power Factor, you actually need to get out the sharp pencil. It doesn't sound like you know what PF is, so there's the first step. For instance, you are ignoring so many other loads that the oven is the lion's share... as such, its particular PF really matters to the overall equation. – Harper Jan 18 '17 at 19:51
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    @EdBeal You refer to a time in the past: did many people have George Foremans, sous vide, curling irons, plug-in 1500W heaters that cost less than an hour's wage, window A/C units for 15 hours' wage, on-demand hot water, "850 watt" gaming PCs, laser printers, 55" TVs, electric lawnmowers, dust collectors, and a plug-in hybrid car? – Harper Jan 18 '17 at 20:34
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    @EdBeal VA is only the same as Watts for a power factor of 1. Inductive loads (like motors) and capacitive loads (like flourescent lights) have a power factor less than 1 because they draw current out of phase with the applied voltage. Only pure resistive loads (or power-factor-corrected loads) have a pf of 1. Wikipedia – brhans Jan 18 '17 at 20:48
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2 KVA per home (2000 watts) is what the power plant uses when they're bragging about how many homes their plant powers. They're talking average use.

What really happens is you have high extremes of power use. The family chef has the oven, 3 burners, a George Foreman and the toaster all working at once (and a crockpot for sauces), the water heater is constantly recovering from dishwashing, and all that heat in the house has forced the AC to 100% duty cycle. Once dinner is called, all those loads will poof disappear.

You have to size the system for peak use.

OK, so you think "fudge factor", but this is like a fudge-factor of fifty. No, you gotta sharp-pencil engineer this out. Or just put in really good service and not worry about it.

Maybe you're thinking about it upside down

You're asking "how little service can I provision". How about asking "how much can I get for sane cost".

Adding electric capacity is dirt cheap. Spend an extra $500/unit on the parts to do it right, and it'll last 40 years, and that's chump change for something that'll last 40 years. It's a loser's game to pinch pennies on service, only be forced to upgrade later. Especially if, once permitted and occupied, the city requires a licensed electrician to do the work. As a homeowner subdividing yourself, you can DIY that stuff for pennies on the dollar.

Ample service also saves money on appliances. Electric on-demand water heaters are half the price of gas, and don't require a vent. My landlord put in a $1200 gas one because he had no choice. Ditto dryers - tenant-grade electric washer-dryers are commodity.

Better service also means better tenants. Tenants who are constantly fighting tripped circuit breakers are going to believe your electric is hokey and you're a slumlord, and are not going to stay. At extremes, "Can a circuit be added for my electric car" is a wonderful question because it means a wealthy tenant who'll be staying awhile. You want to giggle with glee going "Oh yeah! We can do that!"

If the conversation with the electric company goes something like "Well we could bring out 400A service, but it'll cost ya (more than you wanna pay rght now)", then make everything else ready for it, so they can just cut it in without additional work.

If the game is make max money as a landlord, squinting at price tags at Home Depot is barking up the wrong tree.

Commons service

Keep in mind Code will certainly require you to have a separate meter for commons-area loads. This could be impressive, like an electric dryer or shared on-demand water heat; or it could be trivial, like five LED lights.

I have to say, in the latter case, I would consider going off-grid solar for a few LED premises lights. It's far cheaper than the cost of a monthly meter fee.

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I post my experience: in Italy we live well on 4,4kW @230V contract, despite average being 3kW@230V, we just have heating (30kW gas combi) and cooking (5 gas burners). As appliances we have electric dryer, dishwasher washing machine 2 fridges, a refrigerator and electric oven.

If you plan to go "all-electric" 8kW should be enough (Induction cooker, heat-pump heating).

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