I'm looking to install a safety switch (SIEMENS LNF222R) to disconnect a load on my house. Can I run only the hots (black and red) to this box and run neutral and ground to the appliance and still be up to code? Or do I need to run all four wires to the safety switch, put wire nuts onto the ground/neutral wires in the switch, and connect the hots to the switch?

If I run only the red/black, do they need to be inside of a conduit to be up to code? The wires will be run along the ceiling of an unfinished basement.

  • The case is metal on a LNF222R, make certain ground is attached to it. Your really only saving neutral. – Tyson Oct 25 '17 at 0:37

You have two choices

You either can run all the wires to the switch and then run all the wires from the switch to the appliance (using wire nuts or setscrew splice lugs for the neutral and ground if the switch does not provide neutral and ground bars), or you can run the hots, neutral, and ground to the appliance and then run a 240V switch loop out to the switch where the unswitched hots go out and the switched hots come back.

Given that this is likely larger than a 20A or 30A circuit, and /4 NM isn't available in larger than 10AWG, the better choice is to run all four wires to the switch. Using bars vs. nuts or setscrew splices is up to you -- just make sure the switch enclosure is properly grounded via a pigtail if you do the latter, though.

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  • The switch would need to be grounded not sure if that is what you were referring to with the lug part. – Ed Beal Oct 24 '17 at 13:13
  • You don't need /4 NM, do you? Oh yes, yes you do, if neutral is involved. – Harper - Reinstate Monica Oct 24 '17 at 16:05
  • To run all lines to the switch, is it best to install a neutral and ground bars into the switch? – bbarke Oct 24 '17 at 18:08
  • @Harper -- you need /4 even w/o neutral as you are running two hots out and two hots back, + a ground... – ThreePhaseEel Oct 24 '17 at 22:13
  • @ThreePhaseEel if there is no neutral, currents will be equal on L1 and L2, and you can get it done with two /2's. – Harper - Reinstate Monica Oct 25 '17 at 0:44

Topologically, all wiring must be done in a tree style, never a loop or triangle.

You can wire this in a string or a Y, never a triangle.

For instance it's OK to have the supply at the left side of the Y, the appliance at the right side of the Y, and the switch at the bottom. In that case, ground and neutral go across the top two branches of the Y, ground and the two always-hots goes down the left two branches of the Y, and the two switched-hots go up the right two branches.

And this bottom branch is tricky because all 4 conductors must be in the same cable or conduit, and they don't make 4-wire + ground cable in large sizes, so it would need to be conduit.

If you put a clamp ammeter around the clump of wires anywhere on the Y, it would read 0 amps, because the current flows in all the wires would cancel each other out. This means no EMF emissions and no eddy-current heating of anything metal nearby.

When current goes in a loop (the bad thing), the center of the loop becomes the core of a transformer (which is not laminated to prevent eddy currents), and unpredictable things happen, including energy loss, heating of components and disturbing people who are EMF-sensitive. It's kicking up a Rather Big magnetic field, so it's not surprising to me if some people can feel it.

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