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pandora
Premium Member
join:2001-06-01
Outland

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pandora to nunya

Premium Member

to nunya

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

said by nunya:

There's nothing to get hyped up about.
The OP has what everybody incorrectly refers to as a 400A service. It looks fine. They did a nice job (I wouldn't have used SEU on a nice new install like that).

It's really a 320A service, and TBQFH he'll never use it. That transformer on the pole looks to be a 50 KVA, or at the most a 75 KVA. Add to that it is shared with other homes. There *really* isn't 320A even available to the OP.

The utility appears to have provided the service drop. The utility is subject to the NESC, not the NEC. They can pretty much put whatever they feel like in there. Remember, utility work is usually done under engineering supervision. They know that drop will never *really* even see 275A. I doubt it ever sees 200A.

Service size ≠ what's actually available from the utility.

I spoke with the utility today, their belief is the system as installed can maintain 320 amp continuous service. Loads of up to 400 amps may be sustained for long periods (according to the regional installation supervisor). He indicated if at any time, there was a failure to supply 400 amp by the cable or transformer, excluding emergency periods where there are blackouts or brownouts, the electric company is required by law to remediate the service to provide the required load (up to 400 amps sustained).

He indicated the design for all residential 400 amp service assumes no more than 320 amps drawn continuously (he said this is required by state regulation as the minimum the utility must provide).

The wire is 350 kcmil Alcan XLPE 90C, whatever that means. The transformer is 75 KW and feeds 6 homes. When built, all homes in the neighborhood had 75 or 100 amp service. Most now have 200 amp. Street voltage is 8,000 volts to the "main feed" (sometimes he used the word primary apparently interchangeably). Output read with no load to our meter was 246 volts according to the supervisor. I am not at all an expert on these things. He indicated the load was buried approximately 3' underground, with a tracer wire. My electrician had a spare conduit built, in the event there is ever a failure (as the conduit will be paved over by a long driveway).

I don't know if this helps the discussion any, but it occurred to me to ask the people who installed the stuff.

He indicated the street was not scheduled for any upgrade in the near or intermediate future, but that some poles may be replaced, and mine was on the list for an intermediate future replacement. So the pole in the pictures may be a slight concern to the company.

The supervisor indicated while the shunt is installed, they must assume the average use of all homes using the same transformer. He indicated this would save me money, as my use is more than 50% above average.

Jack_in_VA
Premium Member
join:2007-11-26
North, VA

Jack_in_VA

Premium Member

The transformer is 75 KW and feeds 6 homes. When built, all homes in the neighborhood had 75 or 100 amp service. Most now have 200 amp.

If all the other 5 crank up their usage to 200 amp that's 1000 amp which is 600 above what you say the POCO says they can supply.

Something about this setup doesn't make sense
pandora
Premium Member
join:2001-06-01
Outland

pandora

Premium Member

said by Jack_in_VA:

If all the other 5 crank up their usage to 200 amp that's 1000 amp which is 600 above what you say the POCO says they can supply.

Something about this setup doesn't make sense

How utilities manage and calculate electric loads is beyond my understanding (at this time). It's interesting, but the entire project has been interesting, I've learned a lot.

cdru
Go Colts
MVM
join:2003-05-14
Fort Wayne, IN

cdru to Jack_in_VA

MVM

to Jack_in_VA
said by Jack_in_VA:

The transformer is 75 KW and feeds 6 homes. When built, all homes in the neighborhood had 75 or 100 amp service. Most now have 200 amp.

If all the other 5 crank up their usage to 200 amp that's 1000 amp which is 600 above what you say the POCO says they can supply.

Something about this setup doesn't make sense

Even 400 amps doesn't fit a 75 kVA transformer. 240 volts * 400 amps = 96 kVA. It would be 125% overloaded at 400 amps alone, not to mention the other 5 homes. And if Pandora's home is needing all 400, it's likely the other homes are also needing a considerable amount of power. That is, unless Pandora is running the grow lights operation supplying the other 5 homes.

I think that guaranteed 400 amps of continuous service is shared among all the users of the transformers, meaning Pandora's house is likely never to have 400 amps available just to him.
cdru

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cdru to pandora

MVM

to pandora
said by pandora:

The wire is 350 kcmil Alcan XLPE 90C, whatever that means.

350 kcmil means that the wire has a cross sectional area of 350,000 circular mils. A circular mil is an area of a circle 1 mil in diameter. It's an easy way to measure large wires without having to worry about pi. kcmil can also be abbreviated as MCM (M = thousand CM = circular mil) and is usually found for wire gauges larger than 4/0 or 0000 and AWG is used for smaller wires. Take the square root of the kcmils to get the diameter in mils (thousandths of an inch). So √350000 = 591.6 mils = approximately .592 inches in diameter.

Alcan is the manufacture of the wire.

XLPE means Cross-linked polyethelyene plastic insulation. If you're having plumbing done, you may be using the same type of plastic there where it's known as PEX.

90C is the temperature rating on the wire. This go towards how much current a given wire or cable is allowed to carry safely. Common values are 60C, 75C, and 90C. The lower the number, the less current. It also comes into play when you need to derate a cable because of where it's located or how it is ran.

nunya
LXI 483
MVM
join:2000-12-23
O Fallon, MO
·Charter

nunya to pandora

MVM

to pandora
That just confirms what I said. A single phase 75 KW transformer can supply *roughly* 320A @ 100% load.
The utility knows that you'll never draw close to that. The chances of everybody turning everything on at the same time and blowing the transformer or the fuse are slim. If it does happen, they deal with it then.

leibold
MVM
join:2002-07-09
Sunnyvale, CA
Netgear CG3000DCR
ZyXEL P-663HN-51

leibold to cdru

MVM

to cdru
said by cdru:

Even 400 amps doesn't fit a 75 kVA transformer. 240 volts * 400 amps = 96 kVA. It would be 125% overloaded at 400 amps alone, not to mention the other 5 homes.

Technically correct, but not relevant. The 75 kVA rating is the load limit in order to maintain the manufacturer specified service life of the transformer.
Utility companies are well aware that they can far exceed that rating at the expense of a shorter lifespan for the transformer. Given how many pole mounted transformers around here show clear signs of overheating (and how often some of them pop) it appears that our utility company prefers the more frequent replacement to proper sizing of the transformers.

tschmidt
MVM
join:2000-11-12
Milford, NH
·Consolidated Com..
·Republic Wireless
·Hollis Hosting

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tschmidt

MVM

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
Premium Member
join:2007-11-26
North, VA

Jack_in_VA

Premium Member

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

join:2000-04-09
NW Illinois

mattmag to tschmidt

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

join:2001-03-22
Owen Sound, ON

DKS to tschmidt

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...

tschmidt
MVM
join:2000-11-12
Milford, NH
·Consolidated Com..
·Republic Wireless
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tschmidt

MVM

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
MVM
join:2002-02-21
Queens, NY

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whizkid3 to mattmag

MVM

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.