Code Question: Residential Elec Equipment Mfg Suggests Running 120v Conductors In Conduit Without Neutral

[etbrown4]

A similar thread was posted last week but this identifies the issue more clearly.

Reliance Controls makes manual residential generator transfer switches and sells them by the thousands.

On a 6 circuit 30a transfer switch and panel, Instructions tell the installer to route 6) 120v hot wires from 6) breakers in a panelboard out on 6) #12g red conductors to the transfer switch, and back to the panel on 6) #12g black. No circut neutrals to be run.

It is simply a 14' loop on the hot side of these 6 circuits with no neutral present.

The 2 conduits for the 6 circuits are 3/4 pvc, however those conductors do pass through ferrous metal when entering the transfer switch cabinet and the main panel. There are 6 conductors per conduit.

Nec 300.3(b) requires all conductors of the same circuit to be in the same wireway.

Even though when connected we observe no heating at this point, doesn't the setup as described, appear to violate the Nec?

 

[waross]

I'm a rules guy and if the Nec says, in a conduit you must run the neutrals that are part of the circuit with the hot wires. The Reliance instructions and pic seems to violate the Nec.

When on normal power, the wires act as switch legs and the neutrals are superfluous. The NEC does not require neutrals on simple switch legs.
When on the generator the neutrals are needed.

Waross seems to be saying it's low current so it should be ok. What say others?

Not quite. The issue is unbalanced current. If both red and black wires of the same circuit are in the same conduit, the currents will cancel and there will be no unbalance.
If all of the red wires were in one conduit and all of the black wires in the other conduit the currents would add and be unbalanced.
As I understand it, your wiring is correct.
Neutrals. When you are running on the generator, the currents on your three black wires (in each conduit) will add. There will be an equal and opposite current in the neutral that will cancel and there will be no unbalance.
It sounds as if you have a good installation with no magnetic encirclement.

Anecdote.
I was called to replace a 400 Amp Fused Disconnect service entrance switch that had been destroyed by heat corrosion.
I was told that this was at least the third destroyed switch.
The cause?
Improperly run conductors and magnetic encirclement.
The heat of the conduits was heating the conductors and the copper conductors were conducting the heat to the switch.
The maximum load was less than 200 Amps.
The conduits were too hot to hold for more than a few seconds.
I rearranged the conductors properly and everything was "cool".

 

[etbrown4]

With either gen or utility operation, the 3 reds in each conduit bring power from the panel to the switch and the 3 circuits loop through and go back to the original branch circuit wires in the panel.

An expert will have to tell me if the magnetic fields from the red going out and black returning actually cancel each other. Plenty of lit describes this routinely occuring with a normal 120v circuit and a white and black wire.

Is there any reference material describing the precise situation here?

Reliance, i think incorrectly told me the return current from those red and black 15a circuits returned on the #10 neutral connected to the receptacle. I think they are wrong as that's not even in the circuit for the red and black #12 conductors as shown in their drawing., numbered 1-6, especially with utility operation.

 

[waross]

With either gen or utility operation, the 3 reds in each conduit bring power from the panel to the switch

WRONG. Not during a power failure when on generator power.

An expert will have to tell me if the magnetic fields from the red going out and black returning actually cancel each other.

Yes, when on normal power the currents cancel. In each circuit, the current in the red and black are equal and opposite.
When on generator power there will be no current in the red wires.
The total current in the black wires will be cancelled by a current in the neutral that is opposite nd equal to the sum of the wires in the black wires.

Normal power: Red and Black currents cancel.
Generator power: Black and neutral currents cancel.

 

[etbrown4]

Sounds good! Like the bold print!

And a fine point. As described, we have a #10 neutral in each conduit with the red and blacks, and as an abundance of caution we have a 3rd neutral in a piece of romex between panel and switch.

Sounds like maybe we could or should remove the 3rd neutral to assure that all neutrals follow the same path as the hot conductors in either util or gen mode.

In Util its clear that return current is thru the blacks. In Gen mode it seems that neutral is in the receptacle and back to the gen via the cord, and for the blacks leaving the switch it appears they use the white neutral travelling with them back to the main panel.

Thanks for so much help!