Double Throw Question

[howelloregon]

We have a big house that is served by parallel runs of 4/0 metered on the utility pole. A local electrician is trying to convince us that it is ok to wire in one 200 amp double throw on one of the runs of 4/0, but not the other.

Our contention is the possibility of a back feed situation in the house while under emergency conditions. Our suggestion is a 400 amp double throw box, breaking both circuits.

Can you tell me the NEC interpretation of this situation?

Thanks

 

[qcroanoke]

We have a big house that is served by parallel runs of 4/0 metered on the utility pole. A local electrician is trying to convince us that it is ok to wire in one 200 amp double throw on one of the runs of 4/0, but not the other.

Our contention is the possibility of a back feed situation in the house while under emergency conditions. Our suggestion is a 400 amp double throw box, breaking both circuits.

Can you tell me the NEC interpretation of this situation?

Thanks

If they are paralled 4/0 feeding one panel you are correct to say that there will be a back feed back out to the utility when the genset is running. It is not legal. Not sure of the code reference.

If they are 2 runs of 4/0 not in parallel but feeding 2 different panels I would say he could do what you describe. As long as the transfer switch is service rated or has overcurrent/short circuit protection in front of it.

 

[RUWired]

The code references would be 310.4(B)and(C). Also 240.8.

 

[howelloregon]

I believe the parallel runs feed separate panels in the house, however if someone who was unfamiliar with the setup (say the third owner of the house) inadvertently heated up a circuit in the house that was not on the emergency panel (under emergency conditions) - it would be possible to back feed since both runs of 4/0 are tied together in the meter socket.

It's not straightforward, but the lineman on the pole working the primary is not going to like the idea.

 

[hurk27]

I believe the parallel runs feed separate panels in the house, however if someone who was unfamiliar with the setup (say the third owner of the house) inadvertently heated up a circuit in the house that was not on the emergency panel (under emergency conditions) - it would be possible to back feed since both runs of 4/0 are tied together in the meter socket.

It's not straightforward, but the lineman on the pole working the primary is not going to like the idea.

If the 4/0 conductors feed separate panels, then they are not parallel conductors, as far as the NEC is considered, If the transfer switch only transfers one panel I see no problem in this, it is done all the time, when having only certain circuits fed by a stand by generator, just because the 4/0 conductors are connected together at the meter, it wont make a difference., as the other panel is not being fed by the generator.

 

[curt swartz]

If these 4/0's are not connected together at the house as parallel conductors you have a violation of 225.30 or 230.2.

 

[hurk27]

If these 4/0's are not connected together at the house as parallel conductors you have a violation of 225.30 or 230.2.

E.rrrr how so?