Mismatched Electrical Service Wiring

[ienriq]

Hello, I wanted to know if there was any danger in having mismatched service wiring at the mast head as shown in the picture. The wiring was sized for 100 Amp from the utility side and 400 Amp on the residential side. The only potential hazard I feel is localized heating at that connection if anything close to 400 Amps is used from the connected 6 Unit Apartment Building. I could be wrong, but I would definitely appreciate some further information on this.

 

[Dennis Alwon]

The utility always pulls conductors smaller than the NEC allows. Also conductors in free air are rated much higher than conductors in conduit. The power company knows what the need and are not under the NEC's jurisdiction

 

[Coppersmith]

I used to call the poco when I did a service upgrade thinking they might want to beef up their end. They never did.

 

[Jraef]

Ahead of the meter, they own the problem, and as said, they don't have to follow the same rules. That's probably "400A" rated conductors for them.

 

[user 100]

I used to call the poco when I did a service upgrade thinking they might want to beef up their end. They never did.

No matter how old or undersized the triplex may seem, they often won't pull new wire to a residence unless there is something physically (damage from a limb, failing insulation...) wrong with the drop- and even then the new conductors are still gonna be smaller for any given amperage than what we would see in the NEC.

And to the OP: Food for thought -its not so much about what wire size is installed- its more about the actual load carried by those wires. Everything south of the poco connections is rated for 400 amps, but is the overall load really anywhere near that?

 

[electricman2]

I used to call the poco when I did a service upgrade thinking they might want to beef up their end. They never did.

+1

 

[mbrooke]

It might be sized correctly.

1. Wire on a messenger in open air can carry more current before reaching the same temperature.

2. The actual load and the NEC calculated load are often two separate animals. Actual load tends to be 1/3 to 1/2 the NEC, often times less for residential. My own home with a 200amp service could get away with a 50 amp breaker.