Double Throw Question

Status
Not open for further replies.
H

howelloregon

Member
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
 
howelloregon said:
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
Click to expand...

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.
 
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.
 
howelloregon said:
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.
Click to expand...

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.
 
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.
 
Status
Not open for further replies.
Top