70’s 80’s NEC wire ampacity

[blueheels2]

Have there ever been any big changed in the ampacity chart in the past 50 to 60 years?
I have a multifamily apartment where the underground feeder from the transformer to the meter mains failed last night. I have seen the wire in the main/pull box and in the transformer. Wire from the transformer is a single set of 500 AL (2 hots 1 neutral) that comes up through the slab into a junction box. A splice is made in that j/box splitting the 500/s into 2-500’s that land on a 60@ amp breaker.
Power Company (Duke) says that the cable is customer owned, customer problem.
However the wire from transformer to junction box is only rated for 310 amps current NEC. It’s interesting to me that in the j-box below the main they splice and make 2-500’s which would be good for the 600 amps, and send that to the breakers.

Makes me think the wire from transformer to junction box is Dukes wire and from the tap to the breaker is reallly the customers.

Plannning a complete replacement of the wire but due to the way things are wired I could never get parallel 500’s from the transformer to the junction box. Single 3” GRC leaves tap box and goes under the slab and stubs outside of the building footprint. Service is in a step down area slash 1/2 basement. No way to get there.

So am I right in thinking wire from transformer to j-box is under power company rules and from the j-box to the breaker is under NEC? Or when these were built (est 1965-1980) the NEC allowed a single set of 500 Al to feed a multi family dwelling ?

Sorr for the rambling post.

 

[infinity]

So am I right in thinking wire from transformer to j-box is under power company rules and from the j-box to the breaker is under NEC? Or when these were built (est 1965-1980) the NEC allowed a single set of 500 Al to feed a multi family dwelling ?

I don't think there was ever a time where the NEC would allow a single set of 500's to feed the 600 amp breaker. I do think that you're onto something with the JB being the service point so anything upstream of that is not covered under the NEC.

I've seen similar things with ConEd and their "end boxes" where what's coming in from the street is much smaller than what's required by the NEC.

 

[tortuga]

Have there ever been any big changed in the ampacity chart in the past 50 to 60 years?
I have a multifamily apartment where the underground feeder from the transformer to the meter mains failed last night. I have seen the wire in the main/pull box and in the transformer. Wire from the transformer is a single set of 500 AL (2 hots 1 neutral) that comes up through the slab into a junction box.

Review all the definitions under service in article 100. I'd call that a 'service lateral', regardless of who owns or constructs one I don't think it needs over-current protection, and others will correct me if I am wrong article but when dealing with underground article 230 only requires underground service conductors to have over-current protection. You should establish where the service point is with the utility to be sure. If the service point is at the transformer then your dealing with underground service conductors and that changes things...

A splice is made in that j/box

I'd call that the 'service point'

splitting the 500/s into 2-500’s that land on a 60@ amp breaker.

I'd call these the 'service entrance conductors' and 'service disconnect'.

Power Company (Duke) says that the cable is customer owned, customer problem.

regardless of who owns it the NEC rules for underground service conductors only start after the service point.
Presumably the dwelling meters are after all this.

 

[blueheels2]

Review all the definitions under service in article 100. I'd call that a 'service lateral', regardless of who owns or constructs one I don't think it needs over-current protection, and others will correct me if I am wrong article but when dealing with underground article 230 only requires underground service conductors to have over-current protection. You should establish where the service point is with the utility to be sure. If the service point is at the transformer then your dealing with underground service conductors and that changes things...


I'd call that the 'service point'

I'd call these the 'service entrance conductors' and 'service disconnect'.

regardless of who owns it the NEC rules for underground service conductors only start after the service point.
Presumably the dwelling meters are after all this.

Yeah the dwelling meters are after the main breaker. It’s one of those meter packs with the main on the right and then the unit/meter disconnects are to the left and the bus continues through and they all bolt together.

 

[CoolWill]

They only have to be sized to carry the calculated load, I believe.