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tschmidt
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join:2000-11-12
Milford, NH
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reply to leibold

Re: The renovation continues ... today new 400 amp service!

said by leibold:

Utility companies are well aware that they can far exceed that rating at the expense of a shorter lifespan for the transformer.

Yup - I can attest to that from first hand experience.

When we built our house installed a 200A service plus 30A separately metered service for hot water. Except for kitchen stove appliances are electric. Even space heating is electric to backup wood stove.

We are 600 feet off the road so have our own pole pig. Power company installed a 10 KW transformer. Being the good engineer that I am felt obligated to point out that 200A x 240V is 48 KW. The supervisor smiled knowingly and said that was true but transformer has tremendous overload capacity. If we were able to overload it they would be happy to replace it.

Well that was 30+ years, a direct lightning strike, and two kids ago and the transformer is still going strong. It will probably still be there after I'm in the ground.

/tom


Jack_in_VA
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join:2007-11-26
North, VA
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said by tschmidt:

said by leibold:

Utility companies are well aware that they can far exceed that rating at the expense of a shorter lifespan for the transformer.

Yup - I can attest to that from first hand experience.

When we built our house installed a 200A service plus 30A separately metered service for hot water. Except for kitchen stove appliances are electric. Even space heating is electric to backup wood stove.

We are 600 feet off the road so have our own pole pig. Power company installed a 10 KW transformer. Being the good engineer that I am felt obligated to point out that 200A x 240V is 48 KW. The supervisor smiled knowingly and said that was true but transformer has tremendous overload capacity. If we were able to overload it they would be happy to replace it.

Well that was 30+ years, a direct lightning strike, and two kids ago and the transformer is still going strong. It will probably still be there after I'm in the ground.

/tom

That's interesting since my transformer that feeds 4 homes started out at 15 kva, changed to 25 kva, then 50 kva and now 75 kva all without any problems I'm aware of. I'm sure my 300 amp upgrade didn't trigger it since the original drop wire from when the house was 60 amp was installed.


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3
reply to tschmidt

said by tschmidt:

Being the good engineer that I am felt obligated to point out that 200A x 240V is 48 KW. The supervisor smiled knowingly and said that was true but transformer has tremendous overload capacity.

I'm trying to recall exactly what the POCO guy said about the installation here. We're on a 15kW transformer by ourselves. Service for house is 200A. Seems he told me they figure it a bit differently than you did as 15kW / 120V = 125A, and that is *per leg*, so we would essentially have excess capacity with the current configuration. This of course assumes perfect load balancing.

Now, I may be wrong on that, its been awhile since that conversation came up. Just throwing it out for those who know more than me to cuss and discuss...


DKS
Damn Kidney Stones
Premium,ExMod 2002
join:2001-03-22
Owen Sound, ON
kudos:2
reply to tschmidt

said by tschmidt:

Well that was 30+ years, a direct lightning strike, and two kids ago and the transformer is still going strong. It will probably still be there after I'm in the ground.

And full of PCB's...
--
Need-based health care not greed-based health care.


tschmidt
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Milford, NH
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1 edit

said by DKS:

[And full of PCB's...

Unlikely, but not impossible.

The transformer was installed in 1980 when we first moved onto the property. This was around the time of the big PCB scare. I was assured the transformer did not contain PCB. Utilities were going through a big replacement phase at the time so I have no reason to doubt the accuracy of that statement.

In the US manufacture of PCBs was banned in 1980. According the the EPA PCB use in transformers ended in 1977.

»www.epa.gov/reg3wcmd/ts_pcbs.htm

But your post prompted me to double check so I submitted a request to our utility.

/tom


whizkid3
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Queens, NY
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reply to mattmag

said by mattmag:

We're on a 15kW transformer by ourselves. Service for house is 200A. Seems he told me they figure it a bit differently than you did as 15kW / 120V = 125A, and that is *per leg*...Now, I may be wrong on that

Yes, its wrong. 15kVA / 240V = 62.5A. Total. Or per leg. Makes no difference, there is no other way to do the math.

This could be exceeded when necessary, the transformer can be overloaded at a reduction of its life. 15kVA works fine for most homes - on average. That is why utilities often put up to 4 on one 25kVA transformer, which can basically only provide 100A total at rated load.

The OP's 400A service? Note the transformer its fed off of. 50kVA at best, and its shared. It puts out 200A - shared - at full rated load. But a 400A service certainly makes for a nice thread, more than most of us could post if we were trying to impress people with our service.