Utility or Owner Responsibility?

[charlie b]

Existing building being renovated. Existing utility transformer and (I believe) utility-owned service conductors. Thus, the utility-owner transition would be the lugs of the main breaker on the main service panel. That panel is rated 800 amps, and the main breaker is 800 amps. Let us assume a calculated load of 600 amps.

My information is that the service conductors are (2) sets of 500 MCM Aluminum. That has an ampacity of 620. Under NEC rules, you can?t protect a 620 amp conductor set with an 800 amp breaker (i.e., next higher standard size is 700). Furthermore, you can?t take advantage of the ?next higher standard rating? rule in 240.4(B) for transformer secondary conductors. So the breaker has to be 600 or lower.

Here?s the question: Is this something I can ignore, given that the service conductors belong to the utility? Or is it the responsibility of the owner (whose interests are to be safeguarded by the design engineer ? myself) to ensure that the main breaker is capable of protecting the service conductors in accordance with NEC rules? Specifically, should I call for a design change to replace or reset the breaker to a maximum trip of 600 amps?

 

[steve66]

IMO you can ignore it. Since the conductors are owned by the utility the NEC doesn't apply (at least to the OCP sizing).

Some NEC rules do apply which help limit the risk: i.e. a limited distance service conductors can run inside the building.

If you were planning a new service, and you asked for a 600A service, the utility would probably still undersize the service entrance conductors.

However, if you are adding load to the building, I think it is good practice to call the utility and give them the chance to upsize their conductors (which I assume would be at their expense) if they think it is necessary.


Steve

 

[charlie b]

Load is being added to the building. A 30+ day load measurement was taken. The engineer who prepared the "existing load calculation" made at least two errors, so I don't know what the final load will be yet. But it is possible that the final load would be over 620 amps. Would that change anything in your answer?

 

[steve66]

Load is being added to the building. A 30+ day load measurement was taken. The engineer who prepared the "existing load calculation" made at least two errors, so I don't know what the final load will be yet. But it is possible that the final load would be over 620 amps. Would that change anything in your answer?

I would just make sure I contacted the utility, and I would verify that the service conductors are theirs. Also, I'd probably send a fax or an email, or something that I could save to show that I did notify them.

Steve

 

[ceb58]

Where and how is it being metered? CT can?

 

[Jim W in Tampa]

Here any wiring within a building belongs to owner. Have never seen a poco wire to a main breaker. If underground the EC runs to transformer and linesman make connections.

 

[tryinghard]

I would just make sure I contacted the utility, and I would verify that the service conductors are theirs. Also, I'd probably send a fax or an email, or something that I could save to show that I did notify them.

Steve

Ditto Steve but include the calc load. Our local utility provides the load form on residential new construction but often get it from drawings or submitted on all others.