Determining Service Capacity

[Tainted]

I went to a building that had 2 sets of 500kcmil copper service conductors from con-edison going into a CT cabinet, going out of the CT cabinet were 6 sets of 500kcmil copper distributed to various disconnected service disconnects. The amperage size of the CT cabinet is unknown. Do I determine the existing service size based on conductors provided by con-edison or conductors coming out of the CT cabinet?

Suppose NEC 220.87 was performed, do I do the spare capacity calculation based on conductors provided by utility?

 

[DrSparks]

I went to a building that had 2 sets of 500kcmil copper service conductors from con-edison going into a CT cabinet, going out of the CT cabinet were 6 sets of 500kcmil copper distributed to various disconnected service disconnects. My question is, the amperage size of the CT cabinet is unknown. Do I determine the existing service size based on conductors provided by con-edison or conductors coming out of the CT cabinet?

Suppose NEC 220.87 was performed, do I do the spare capacity calculation based on conductors provided by utility?

No, the utility has their own methods to determine wire ampacity. What do you mean 6 sets? Do you mean six wires total or six of each phases / neutral?

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[Tainted]

No, the utility has their own methods to determine wire ampacity. What do you mean 6 sets? Do you mean six wires total or six of each phases / neutral?

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Meaning each phase has 6 conductors. So for instance, 6 sets of 500 copper is about 2280amps, that means the service size is about 2000Amps? I wish there was a way to find what the CT cabinet is rated, there's no nameplate on it.

 

[DrSparks]

Meaning each phase has 6 conductors. So for instance, 6 sets of 500 copper is about 2280amps, that means the service size is about 2000Amps? I wish there was a way to find what the CT cabinet is rated, there's no nameplate on it.

Yeah that sounds about right. Well if it can accommodate 6 sets of 500 MCM and the lugs are rated to terminate that size wire and there's sufficient gutter space to accommodate wire bend radius, I'd say you're ok. I would think enclosure dimensions would be the best way to determine the amperage rating of the cabinet.

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[Tainted]

Yeah that sounds about right. Well if it can accommodate 6 sets of 500 MCM and the lugs are rated to terminate that size wire and there's sufficient gutter space to accommodate wire bend radius, I'd say you're ok. I would think enclosure dimensions would be the best way to determine the amperage rating of the cabinet.

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Ok thanks for your input. So is this evidence that NEC article 220 is broken since con-edison always provides incoming service conductors much lower than the downstream conductors? Am I missing something?

 

[DrSparks]

Ok thanks for your input. So is this evidence that NEC article 220 is broken since con-edison always provides incoming service conductors much lower than the downstream conductors? Am I missing something?

The utility company is not subject to the governance of the NEC, they are subject to the governance of the NESC (National Electrical Safety Code). They have engineers to determine ampacities based on area usage and diversity factors that we as electricians are not qualified to make.

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[Tainted]

The utility company is not subject to the governance of the NEC, they are subject to the governance of the NESC (National Electrical Safety Code). They have engineers to determine ampacities based on area usage and diversity factors that we as electricians are not qualified to make.

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I knew that and I get it. My point is, this just shows how overkill article 220 is... The amount of money spent on electrical infrastructure due to these overkill calculations mandated by the NEC is crazy.

 

[DrSparks]

I knew that and I get it. My point is, this just shows how overkill article 220 is... The amount of money spent on electrical infrastructure due to these overkill calculations mandated by the NEC is crazy.

No I hear you. It makes sense. The same current passing through the POCOs wires passes through the premise wiring. I can tell you that just about every overhead 100 amp to 200 amp service upgrade I've ever done, the utility company simply reattached the exact same service drop.

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[electrofelon]

I knew that and I get it. My point is, this just shows how overkill article 220 is... The amount of money spent on electrical infrastructure due to these overkill calculations mandated by the NEC is crazy.

Yep. Welcomec to the absurdity of the NEC. Perhaps the worst document in the history of codes and standards. Almost every day I think about leaving the electrical trade due to the NEC/NFPA....and it only gets worse every cycle.

 

[Tainted]

Yep. Welcomec to the absurdity of the NEC. Perhaps the worst document in the history of codes and standards. Almost every day I think about leaving the electrical trade due to the NEC/NFPA....and it only gets worse every cycle.

I’m glad I’m not crazy for thinking this. I’m suprised article 220 survived this long without it being completely revised.

 

[electrofelon]

I’m glad I’m not crazy for thinking this. I’m suprised article 220 survived this long without it being completely revised.

I am baffled many articles in the NEC have survived so long without being substantially revised. It's even more baffling that there is seemingly no competition to such a horrible code document and incompetent publisher.

 

[Tainted]

I am baffled many articles in the NEC have survived so long without being substantially revised. It's even more baffling that there is seemingly no competition to such a horrible code document and incompetent publisher.

This brings up a interesting question, shouldn’t service sizing be a perfomance issue rather than a safety issue? Kinda like voltage drop is a performance issue rather than a safety issue as states by the NEC. I mean as long as the overcurrent protection is sized based on the feeder and short circuit, I don’t see any safety issue. This makes me then feel like there’s no purpose of article 220. You could have a undersized service or oversized service and still have it be completely safe as long as overcurrent protection, feeder, and short circuit current is considered

 

[electrofelon]

This brings up a interesting question, shouldn’t service sizing be a perfomance issue rather than a safety issue? Kinda like voltage drop is a performance issue rather than a safety issue as states by the NEC. I mean as long as the overcurrent protection is sized based on the feeder and short circuit, I don’t see any safety issue. This makes me then feel like there’s no purpose of article 220. You could have a undersized service or oversized service and still have it be completely safe as long as overcurrent protection, feeder, and short circuit current is considered

I agree. I've never understood the NEC's and inspectors' obsession with load calcs.

 

[infinity]

This brings up a interesting question, shouldn’t service sizing be a perfomance issue rather than a safety issue? Kinda like voltage drop is a performance issue rather than a safety issue as states by the NEC. I mean as long as the overcurrent protection is sized based on the feeder and short circuit, I don’t see any safety issue. This makes me then feel like there’s no purpose of article 220. You could have a undersized service or oversized service and still have it be completely safe as long as overcurrent protection, feeder, and short circuit current is considered

If a load calculation states that a new house requires a 400 amp service do you really think that the new homeowner is well served by a 100 amp service that trips the main when the AC turns on? I agree that Article 220 can use some work but getting rid of load calculations is IMO pretty silly.

 

[Tainted]

If a load calculation states that a new house requires a 400 amp service do you really think that the new homeowner is well served by a 100 amp service that trips the main when the AC turns on? I agree that Article 220 can use some work but getting rid of load calculations is IMO pretty silly.

So what if it keeps tripping? If the service is undersized that’s not a safety issue. The circuit breaker is doing it’s job.

 

[infinity]

So what if it keeps tripping? If the service is undersized that’s not a safety issue. The circuit breaker is doing it’s job.

You don't think that a main circuit breaker tripping on a new home because the service is grossly undersized is a problem? I realize what it says in 90.1 about adequacy but building codes in general aren't only about safety. The NEC says that it is not a design manual but most agree that is not true.

 

[electrofelon]

If a load calculation states that a new house requires a 400 amp service do you really think that the new homeowner is well served by a 100 amp service that trips the main when the AC turns on? I agree that Article 220 can use some work but getting rid of load calculations is IMO pretty silly.

I have a hard time believing this would actually happen with any significance and be an issue. Look at hvac systems for example, where they generally do not have to be engineered for residential size systems. how often do you hear of a system that doesn't have adequate heating or cooling capacity? there is really no incentive for a tradesperson to install an inadequate system that the customer will be unhappy with.

 

[Tainted]

You don't think that a main circuit breaker tripping on a new home because the service is grossly undersized is a problem? I realize what it says in 90.1 about adequacy but building codes in general aren't only about safety. The NEC says that it is not a design manual but most agree that is not true.

It’s a problem for sure, but what I’m saying in my opinion is that it’s not a safety problem. There’s a reason NEC claims it’s not a design manual, that’s because all they care about is safety, there’s many things in the code that contradicts this. Article 220 is one of them.