I have a goal to replace all the switches in my house and then pass inspection. I'm following NEC 2020, and must meet NEC 2008 for the local code.

Everything was going well until I removed the cover from the furnace service switch. After peeking inside there, I'm uncertain if it's worth replacing that one.

Switch and box Conduit detail

Here are my concerns and questions.

  1. Box is not grounded. No green screw present, and other end of metal conduit is not attached to anything. Should be as simple as splicing a pigtail or two, but need to look into whether the furnace is even grounded properly.
  2. Thermostat and compressor cables pass through the box. Is that allowed, or would I have to reroute and extend those cables to the knockout on the other side of the furnace?
  3. No bushings used on either end of metal conduit. Near the ceiling, it's a NM cable entering the bare conduit, and it's visible just by looking up above the furnace. I've never used that material before, but I'm guessing I would have to remove the entire conduit and start from scratch to do it the right way? Or is there an "old work" method to protect the ends?
  4. Wires visible through the conduit clamp. Is this missing a bushing?
  5. Messy work with electrical tape and the one ground wire is in contact with the bottom edge of a wire nut. This part might be legal but I'd do it differently.

Edit: Photos of furnace interior.

No clamp or bushing used here. Furnace has a junction box and ground screw that are unused.

Back side of box Furnace junction box is empty

  • 2
    #2, yeah... It's obvious where they come in from, but where to they go from this box? They're generally low voltage and AIUI, you're not allowed to mix LV and line voltage in the same box.
    – FreeMan
    Oct 25, 2021 at 18:22
  • The knockout at the back bottom of the handybox is mounted to the furnace knockout. The hi and lo wires all go through the same hole in the back Oct 25, 2021 at 19:34

1 Answer 1

  1. The box needs to be grounded by screw or clip, the switch being attached to a metal box satisfies grounding the switch. (I would remove the paper washer, but 404.9(B)(1) doesn't seem to require it.)

  2. The low voltage thermostat wires should enter furnace through their own penetration. The NEC does allow "All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway", but you may have furnace UL/CSA/ETL Listing issues where cable enters the furnace. So best just to avoid if possible.

  3. There should be a bushing or connector at the top of the flex. Yes, you will need to remove the wire.

  4. Where connected to box no bushing is required, but the little round hole is an inspection hole to verify that the flex is fully inserted into connector, or in this case to see it isn't.

  5. Sorry, I don't understand.

(6.) The holes where the wires go from box into furnace need a connector such as a chase nipple and locknut.

(7.) The line voltage wires should not be squeezed past compartment barrier and sidewall insulation. Actually from this limited view I can't tell for sure but but my suspicion is that the line voltage enters the furnace in a compartment that line voltage may not be allowed.

  • Thank you for the detailed answer. I'm thinking the line wires are supposed to be run in the conduit to the opposite side of the furnace where the internal junction box is located, grounded in both boxes, and totally separate from the low volt wires. To put that another way, the service switch box is in the wrong place, and I'll need an extra junction somewhere to make the circuit long enough. Not sure if this all falls within the scope of my permit, but I will be confident that I know what's going on in the end. Oct 25, 2021 at 23:28
  • 2
    If the jots and tittles of the scope of your permit don't technically cover your work and I would expect the inspector would just be satisfied that a home owner actually got a permit. Oct 25, 2021 at 23:37

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