TRANSFER SWITCH NEUTRALS

[mike9593]

I am installing a 20KW generator in a NON DWELLING application. There is an existing 200 amp main distribution panel and a 100 amp sub panel. I will be selecting various circuits from each panel and have installed a 3/4" EMT conduit from each panel to the transfer switch (with load center). I have seen many installations of transfer switches wired without neutrals brought over. I have also noticed that the Reliance brand and other manual transfer switches only carry one neutral and one ground wire to them.
The main panel has just a neutral bar and of course, the sub panel has a neutral bar and a ground bar. The transfer switch has both a neutral bar and a ground bar.

Can I bring over all the hot wires and just one neutral and ground wire to alleviate overheating in the ferrous 3/4" conduit? (300.20)
I'm not sure that will be OK since there will not be current in the neutral wire.

It seems redundant to bring over all the neutrals and grounding conductors, since they are already landed properly in the existing panels.
Also, how are the grounding conductors handled when some are landed on the neutral (main) and some on the ground bar (sub) going to one transfer switch?
It is a church basement, so I did not want to use PVC.

 

[don_resqcapt19]

Your drawing looks like you are feeding 100 amps of normal power to the transfer switch panel and it looks like that transfer panel has branch breakers in it for the loads that are to be served by the generator. You need to disconnect all of the wires (ungrounded, grounded, and grounding) for the circuits in the existing panels that are to be served by the generator, and extend those wires to the transfer switch panel. These circuits will have wires connected in the existing panel. The only connections will be in the transfer switch panel.

 

[luckylerado]

Don is correct. You must bring all of the conductors of the branch circuit. In your case the ATS is a sub panel of whichever panel you feed it from and may require the installation of a bar because ATS manufactures are el'cheapo.

The Neutral will most definitely have a load and there are additional labeling requirements if you splice the emergency circuits within the panel boards. Splicing does not mean leave it landed on the bar either. The correct way would be single neutral to neutral connections for each branch circuit.

The grounding conductor should be sized to the OCP device serving "Normal Power" to the line side of the ATS. Grounded conductor size will be based on 250.122 if there is OCP at the ATS line side or based on the ungrounded circuit conductor size if it is a main lug type ATS.

 

[kwired]

Don is correct. You must bring all of the conductors of the branch circuit. In your case the ATS is a sub panel of whichever panel you feed it from and may require the installation of a bar because ATS manufactures are el'cheapo.

The Neutral will most definitely have a load and there are additional labeling requirements if you splice the emergency circuits within the panel boards. Splicing does not mean leave it landed on the bar either. The correct way would be single neutral to neutral connections for each branch circuit.

The grounding conductor should be sized to the OCP device serving "Normal Power" to the line side of the ATS. Grounded conductor size will be based on 250.122 if there is OCP at the ATS line side or based on the ungrounded circuit conductor size if it is a main lug type ATS.

If it is an optional stand by system there are no "emergency" circuits.