Rating of utility service conductors in NYC

Tainted

Tainted

Senior Member
Location
New York
Occupation
Engineer (PE)
Con-Edison usually provides 500MCM copper service conductors into NYC buildings

I know utilities have their own method for determining ampacity of their conductors, but does anyone here know what their 500MCM copper are rated for or the methodology used? Surely it's not as simple as looking at the NEC tables, but is 380 amps per every set of 500MCM copper a good estimate?
 
don_resqcapt19 said:
Not for a utility...it is likely much higher than that. Also, they size their conductors based on known real world loads, not the vastly inflated loads that result from the use of Article 220.
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I figured the 500MCM might be higher, but I just wonder what value or at least an estimated value of the ampacity would be
 
Being that utility companies do not have to follow the NEC they constantly use severely undersized conductors. Years ago while upgrading a center city house from a single 60 amp meter to a 100 & 200 amp services I begged the utility to replace the #6 gauge 1920 era rubber & cloth covered wires with larger wires. Told me being it was an underground service the earth prevents the wires from over heating and did not need to be replaced. Every 400, 600 & 800 amp aerial service that I installed they only used 4/0 aluminum wire to feed them. Top of my o!f head believe 500 MCM copper THWN wire is rated for 380 amps. Years ago we were allowed to parallel two sets of #500 MCM copper to feed 800 amp services. Surprised they use copper for service conductors.My house was built in 1962 and the utility company used 4/0 aluminum conductors for rear buss to feed 12 houses.
 
electrofelon said:
FIFA 😉
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Think you mean unrealistically sized conductors. There is no way that they should be allowed to use old rubber covered #6 copper that for us is usually rated for 60 Amps to feed 300 amp total service that I did ( one 100 amp & A 200 amp meters ). Granted that combined loads might only be 120 to 150 amps with both central AC running along . Here is a great example of their penny pinching. A store on a busy street that was built in the 1930's reported smoke coming out of their side walk!. Utility company dug up the side walk and rather then replace old service wires resplicecd a bad section. A few months later side walk started smoking again and caused a fire. Store was originally a small variety store with a 60 amp service. Over the years it was converted to place that had central AC installed, several freezer & refrigerators and service increased to 200 amps but the cheap penny pinching utility company never upgraded the most likely rubber & cloth covered inferior #6 copper service conductors to the basement end box.
 
garbo said:
Think you mean unrealistically sized conductors. There is no way that they should be allowed to use old rubber covered #6 copper that for us is usually rated for 60 Amps to feed 300 amp total service that I did ( one 100 amp & A 200 amp meters )
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Realistically sized based on their knowledge of the real world loads...not loads based on the very very conservative Article 220 load calculations.
 
garbo said:
Told me being it was an underground service the earth prevents the wires from over heating
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That just says they were blowing smoke at you. And it's not penny-pinching, it's having enough information to draw more accurate conclusions than the NEC assumes. I've got a 100amp service, but unless I have two electric heaters going in the winter, which seldom happens, the average load is under 2kw and usually closer to 1.
 
Tainted said:
Con-Edison usually provides 500MCM copper service conductors into NYC buildings

I know utilities have their own method for determining ampacity of their conductors, but does anyone here know what their 500MCM copper are rated for or the methodology used? Surely it's not as simple as looking at the NEC tables, but is 380 amps per every set of 500MCM copper a good estimate?
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Here the utility sizes the service conductors based on their transformer when its one transformer per building.
 
I a
zbang said:
That just says they were blowing smoke at you. And it's not penny-pinching, it's having enough information to draw more accurate conclusions than the NEC assumes. I've got a 100amp service, but unless I have two electric heaters going in the winter, which seldom happens, the average load is under 2kw and usually ccl
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Agree with only consuming an average if 2 KW a hour spread out over a 30 day bill. That is what my house averages. I have done countless residential service upgrades since the 1960's . It was upsetting when I would climb up a ladder to cut an old service cable from utility rear buss that feed 20 or more row homes. Even in morning shade with everybody running AC units the air cooled 4/0 aluminum wire would be very warm especially points closest to transformer. Found it interesting while doing two services on the same block the very warm utility wire close to transformer ( drawing a lot more ampere ) then the same wire at the end of block was mire difficult to skin insulation off of. I posted a few months ago where the utility company refused to upgrade a 75 KVA pole transformer when I installed a 800 amp three phase service to an injection molding shop that ran 24/6. I notified the utility company that they would be drawing around 650 amps 24 /6.The transformer already had a 200 & A 600 amp service feed from it. So in their thinking a transformer that is only rated to produce approximately 180 amps is okay for over 1,000 amps. Within a month existing transformer burned out and penny pinchers replaced it with the same size ( 75 KVA ).The new transformer case turned dark brown within a week or so and burnt out maybe six months later. Last I heard business owner got his lawyer involved with demanding reliable power.
 
I had a customer pulling near max 200 amps continuous single phase on a 200 amp service with what was probably originally a 15 or 25 kva tx. Said he could hear it boiling up there. The poco came and replaced it with a 50 right quick after he called, it was a very fire prone area.

garbo said:
Agree with only consuming an average if 2 KW a hour spread out over a 30 day bill. That is what my house averages. I have done countless residential service upgrades since the 1960's . It was upsetting when I would climb up a ladder to cut an old service cable from utility rear buss that feed 20 or more row homes. Even in morning shade with everybody running AC units the air cooled 4/0 aluminum wire would be very warm especially points closest to transformer. Found it interesting while doing two services on the same block the very warm utility wire close to transformer ( drawing a lot more ampere ) then the same wire at the end of block was mire difficult to skin insulation off of. I posted a few months ago where the utility company refused to upgrade a 75 KVA pole transformer when I installed a 800 amp three phase service to an injection molding shop that ran 24/6. I notified the utility company that they would be drawing around 650 amps 24 /6.The transformer already had a 200 & A 600 amp service feed from it. So in their thinking a transformer that is only rated to produce approximately 180 amps is okay for over 1,000 amps. Within a month existing transformer burned out and penny pinchers replaced it with the same size ( 75 KVA ).The new transformer case turned dark brown within a week or so and burnt out maybe six months later. Last I heard business owner got his lawyer involved with demanding reliable power.
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There are certainly cases of undersized transformers, of course it happens, but the question is how frequently does it happen. How many transformers do you see that have NOT failed from overload? It is most economical for the power company to be burning up a few here and there.
 
electrofelon said:
There are certainly cases of undersized transformers, of course it happens, but the question is how frequently does it happen. How many transformers do you see that have NOT failed from overload? It is most economical for the power company to be burning up a few here and there.
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The bigger the outfit, the larger unplanned energetic thermal event they can afford to absorb into their operating budget now and then.

Us mom and pops can't afford to have something like that happen that we have to pay for, but they can.
 
electrofelon said:
There are certainly cases of undersized transformers, of course it happens, but the question is how frequently does it happen. How many transformers do you see that have NOT failed from overload? It is most economical for the power company to be burning up a few here and there.
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If you oversize your transformers, you end up with low lagging power factor. You have to size them for real world loading, not some imaginary world with 1400 sf houses are drawing 200 amps 24/7. In the real world you are lucky if they are even drawing 20 amps for any significant amount of time
 
electrofelon said:
There are certainly cases of undersized transformers, of course it happens, but the question is how frequently does it happen. How many transformers do you see that have NOT failed from overload? It is most economical for the power company to be burning up a few here and there.
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My neighborhood has homes ranging from 2500 to 4500 SQFT, some all electric. Pairs of homes fed from a 25 kva transformer. I’ve lived here since 1999 and there hasn’t been a single failure. I guess it’s possible one failed and was replaced while I was on vacation, but I doubt it.
 
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