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Old 03-09-2017, 04:30 AM #1
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Default Pole pig and electric service question.

I live in the USA so my house's electric service is 240V split single phase. The main breaker on the service panel is 200A.

But 200 amps at 240 volts is 48kVA. The pole pig feeding my house is 25kVA, and there are three other houses (4 houses total) connected to it. I assume this is fine because most houses will run high-power appliances at different times, and the transformer is probably rated to handle some excess load in cases of overlap.

I say our pole pig is 25kVA because there's a big "25" on the side of it. Generally, in most cases that number seems to be the kVA rating.

What happens if I decide to be stupid and build something big that's capable of pulling 200A and running my service flat out? Wouldn't that be likely to cook the transformer? I don't think my neighbors (or the electric company) would appreciate pole pig bacon for dinner, even though the explosion would probably be pretty cool.

It seems like these houses should be on a 50kVA transformer for better safety margin. The transformer that used to feed our house actually did explode, but I think it was pretty old. That was probably 20 years ago, so the "current" transformer has been working for that long.


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Old 03-09-2017, 05:37 AM #2
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Default Re: Pole pig and electric service question.

If it is rated for 25Kva continuous and you try and pull 48Kva plus the load present at the time on the other three homes , it could case the voltage to sag a lot but I would say the transformer would be fine for a very short duration but that depends on much of over an overload margin it has .

We only have an 80A main fuse in are house , with a 230V Supply .

I wouldn't recommend doing it : P
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Last edited by DashApple; 03-09-2017 at 05:40 AM.
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Old 03-09-2017, 07:52 AM #3
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Default Re: Pole pig and electric service question.

Difference Between kVA and kW | Difference Between

Just look at your power bill, my house uses 1500 KWH per month, that's 50 KWH per day divided by 24 hours is ...hell at 30.4 average days a month we will just call it 2 KWH average continuous, the 200 amp service or 100 amps each side is in case I am running my house AC and a welder in the garage and a bunch of other stuff all at once and it still won't add up to anywhere near that.

Even your breaker box typically has more breakers under your main than the main's value, they all add up to more than that because they will never all be at capacity.

We have 6 houses on each 50KVA pole pig and only in the summer do we have a glitch when everyone is running their AC and ovens on the weekend, the fuse at the front of my neighborhood is 80 amps at 10050 volts and it rarely pops, we have more 50KVA pole pigs than that 80a fuse could possibly carry at capacity, but everything is never at full capacity all at once, well they keep building and each summer we have more and more outages, our CNC guy at the machine shop I worked in years ago would get mad as hell and walk out a few times a month in the summer because the machine would drop his program and break the tool it had chucked, he once spent an hour fixing everything just to have it glitch again, he threw down his wrench and said Fucx it I'm going home.
Yes the shop was on 3 phase but the sub station was loaded in the summer and apparently more people are at home not working these last 20 years and they keep building houses and adding them to the same decades old overbuilt system.

That's ok, led light bulbs will save the day...actually they have lowered my power bill.

-----------that webpage was hanging up, here's a copy.------------

kVA is known as the ‘apparent power’ of a particular circuit or electrical system. In direct current circuits, kVA is equal to kW, because voltage and current do not get out of phase. However, ‘apparent power’ and ‘real power’ (which is expressed as kW) may differ in alternating current circuits. kW is simply the amount of actual power that does valid work. It should be noted that only fraction of kVA is accessible to do work, and the rest is an excess in the current.

Solving for the kW (real power) requires another variable called the Power Factor (PF). That so-called Power Factor is a nebulous value that can vary for every appliance or electrical device. In essence, the value of the Power Factor is either given in a percentage, or 0 to 1, wherein 100 percent (or 1) is considered as unity. The closer the Power Factor is to unity, the more efficient a particular device is with its use of electricity.

Unity is practically present in DC circuits, which creates no difference between the kVA and kW. A device uses less kW when the voltage is out of phase with the current. At the same time, the Power Factor naturally lowers in the process. Power Factor will either be leading or lagging, depending on which way the load shifts the phase of the current with respect to the phase of the voltage.

The relationship between the three (kVA, kW, and Power Factor) is mathematically described as:

kW = kVA x Power Factor; kVA = kW / Power Factor; Power Factor = kW / kVA

In DC circuits, the power factor is mathematically inconsequential, because it is in unity.
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Last edited by RedCowboy; 03-09-2017 at 08:57 AM.
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Old 03-09-2017, 02:28 PM #4
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Default Re: Pole pig and electric service question.

Heh I remember all the fun I had doing kva , kw , kvar calculations
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Old 03-11-2017, 12:14 AM #5
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Default Re: Pole pig and electric service question.

There could also be a breaker around the transformer (primary or secondary) to protect it from a situation where all connected users decide to use maximum power at the same time.

Lets consider my situation for scale: I live in an appartment tower with 132 houses in it, each have 5 electrical groups fused at 16 amps each (all 230v, phases randomly split among groups).

If you presume the absolute worst case, with all groups connected to the same mains phase (which could be so as we don't formally have 3 phase power) this building could draw 132x5x16 amps, a bit over 10 kA, and just short of 2.5 MW. Peak use could be double that since our fuses will tolerate double the current for about a minute before triggering as well.

So would the mains hold if we all decided to put 32 amp loads on every group at the same time? Hell no - that'd b 20 kA going in, while the hole building is fused at something lik 2 kA.
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