400 Amp Utility Meter Socket AIC rating

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steve66

steve66

Senior Member
Location
Illinois
Occupation
Engineer
I have a new service with a new Siemens meter stack, that includes a 400 amp meter. (I think its actually a class 320 meter). The available short circuit current at the meter stack is 35KAIC.

The meter has a 65K rated breaker on the line side of the meter, but the shop drawings indicate the meter only has a 25 KAIC rating.

I asked the rep why the rating on the meter is lower than the breaker rating, and the engineer he asked said its because the breaker has a let through current of more than 30K.

The rep. also said all their 400 amp meter bases have the same 25KAIC limit.

Questions:
1. Surely people put 400 amp meters on systems with more than 25K available all the time. Is this a compliant install? I would think not.
2. If its not compliant, how can I make it so? Would installing a current limiting fuse make this code compliant?

Common sense tells me this isn't a safe installation, but I also have a feeling there must be installs like this going in every single day.
 
Meter sockets do not and cannot have AIC ratings, instead they have Short Circuit Ratings (SCCR) or Withstand ratings.
Amps Interrupting Capacity (AIC) is associated with protective device intended to clear fault currents. these devices are applied per NEC 110.9.
Devices like meter sockets, and even non-fused disconnects, are intended to remain closed until an upstream protective device operates. These items have withstand ratings, and are typically applied per NEC110.10.

That said.
In Wisconsin, one of the POCOs has this in their meter manual:
"Meter sockets are exempt from fault current requirements per NEC 230.66, manufacturer testing issues, and Wisconsin chief electrical inspector ruling of May 1989."
 
Yes, but this is a combination meter socket/circuit breaker, so they do list a "Maximum AIC" of 25,000.

I really don't understand that because the breaker alone has a 65KAIC rating. And its quite common (around here anyway) to install a meter on the line side of the breaker, where the meter socket wouldn't have any protection.
 
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