Grounded conductor size for ATS

[curt swartz]

That only works if the grounded conductor is broken in the switchboard.

Cheers, Wayne

Yes, the wires would be disconnected form the switchboard and extended into the XFER switch.

 

[electrofelon]

If your (unswitched) grounded conductor is a tree (no loops), and your ungrounded conductors always are in the same pipe as their associated grounded conductor (except for switch loops), then there is never an imbalance.

If you leave the grounded conductor continuous in the switchboard, and run just one pipe (ignoring parallel sets) from the switchboard to the ATS, which has one grounded conductor and the utility side ungrounded conductors and the load side ungrounded conductors, all is well. When on utility power, there will be no current on the grounded conductor, but it will be a switch loop with no net current. When on generator power, only the load set of ungrounded conductors will carry current, and the grounded conductor will carry the unbalance on those back to the generator, so again the net current is zero.

Cheers, Wayne

Right, but there is no way to keep the neutrals all connected in the switchboard and use multiple metallic raceways to the ATS correct?

 

[wwhitney]

Right, but there is no way to keep the neutrals all connected in the switchboard and use multiple metallic raceways to the ATS correct?

Sure, what jaggedben said in post #14.

If I understand correctly, you want to have 6 sets for the utility supply to the ATS, and 6 sets for the supply to the loads from the ATS. You were planning to use 6 conduits, 3 of which would each contain 2 sets for the utility supply, and 3 of which would each contain 2 sets for the supply to the loads.

With the exact same conduit configuration, instead put in each of the 6 conduits 1 set for the utility supply, 1 set for the supply to the loads, and 1 grounded conductor.

Cheers, Wayne

 

[electrofelon]

Sure, what jaggedben said in post #14.

If I understand correctly, you want to have 6 sets for the utility supply to the ATS, and 6 sets for the supply to the loads from the ATS. You were planning to use 6 conduits, 3 of which would each contain 2 sets for the utility supply, and 3 of which would each contain 2 sets for the supply to the loads.

With the exact same conduit configuration, instead put in each of the 6 conduits 1 set for the utility supply, 1 set for the supply to the loads, and 1 grounded conductor.

Cheers, Wayne

Ok but im still not following jiw that works. Yes the "ins" and "outs" will cancel, but with the neutrals connected in the switchboard and in the ATS, isn't a wild card as to what current flows through the grounded conductor?

 

[wwhitney]

Ok but im still not following jiw that works. Yes the "ins" and "outs" will cancel, but with the neutrals connected in the switchboard and in the ATS, isn't a wild card as to what current flows through the grounded conductor?

No, the grounded conductor (treating identical parallel conductors as one conductor, as we do) would be a tree, so there is only one path between any two points. So there is no question of how current divides (other than in parallel conductors, where we assume it divides perfectly). While on utility, the only path for grounded current from the loads to the utility is straight through the switchboard. There will be no current on the new grounded conductor going to the ATS. And while on generator, the only path for grounded current from the loads to the generator is to the switchboard and along the new grounded conductor you are running to the ATS.

Another way of putting it is that with your original proposal of grounded conductors both to and from the ATS, there would be basically no current on the grounded conductor from the switchboard to the ATS at any time. So you could just delete it and leave only the grounded conductor from the ATS to the loads (which is obviously required while on generator). But then it should be clear that while on utility the ungrounded conductors to the ATS would have net non-zero current. So you take care of that by sticking them in the same pipe as the ungrounded conductors from the ATS to the loads, like a switch loop.

I think drawing a two-line diagram, one line for the grounded conductor (solidly connected everywhere), and one line for the ungrounded conductors in aggregate (switched by the ATS), should help clarify what I'm saying.

Cheers, Wayne