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I bought Leviton “black and white professional” 20 amp 125V nylon connector(#5369 NEMA 5-20R) and plug(#5366 NEMA 5-20P)for my dishwasher. Both the dishwasher powerline from the panel box and the dishwasher line have solid 12 AWG wire (20 amp). But the instructions to both the connector and the plug both emphatically say “DO NOT use with solid wire”. Why is this? Is it dangerous? enter image description here

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  • Can you post photos of both ends of the wiring in question? – ThreePhaseEel Apr 16 '18 at 3:49
  • Can you post a photo of the end of the dishwasher's wiring, even if it's already got a plug wired to it or the likes? – ThreePhaseEel Apr 16 '18 at 4:13
  • I just now posted the second photo. (See within the question). I forgot to say that the wires are all solid copper (no aluminum or any other metal). I hope that little tidbit helps. – MJCallinall Apr 16 '18 at 4:26
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    Why do you need (or want) to have the dishwasher use a plug/receptacle? Why not have it hard-wired (wire nut the cables together)? In the rare instances where you need to work on the dishwasher, turn off power at the circuit breaker. – manassehkatz Apr 16 '18 at 14:32
  • My friend who installed the dishwasher for me four years ago installed a 15 amp plug and connector, which caused the problem. So I replaced it with a 20 amp plug and connector. “Force of tradition“ so to speak, I guess. – MJCallinall Apr 21 '18 at 17:11
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Because that type of plug is specifically made to be used with cordage, which is electrical cable made to be a flexible cord. "Cordage" and "solid-core wire" are a contradiction of terms.

The cable you are trying to use is Romex, which is made only for permanent installation inside the walls of buildings. It's cheap per foot, since it has none of the wire protections of cordage, and this cheapness is why it's so widely misused as cordage.

You have two choices.

  • The wiring provided with the dishwasher is intended to be hardwired into the building. Use a proper cable clamp where it enters the junction box, and you're all set.
  • Or, pull the dishwasher out, visit your local electrical supply house (big-box stores will only mislead you on something this specialty) and obtain proper cordage sized for the dishwasher, with or without pre-molded plug. I like to buy my cordage with pre-molded plug attached, either from an electrical supply, McMaster-Carr or simply by hacking down an extension cord (provided the cable itself has the correct ratings on it.)

If all this malarkey is because someone told you that you need a GFCI on the dishwasher, there are other ways to solve the GFCI problem that don't involve putting a receptacle there. Ask.

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Solid Romex style electrical cable is not designed for use as portable extensions or cords. The main reason for this is that the solid wires are not flexible and will eventually crack if flexed too much. The cable jacket is also not designed for it can be moved around, stepped on or driven over.

So with the understanding that the cable has to be flexible stranded wire it is also a requirement that the plug ends attached to the cable have to be designed for stranded wire as well.

  • But since this connection will not in use be flexed, would it be safe in practice to have this plug connected to the solid copper? It would not be in compliance with the code, but would it be safe? I suppose what could happen is that when pushing the dishwasher into place the wires being stiff could pull the connectors apart so that the connection was not fully engaged and would get hot? Unlikely but possible, right? So what is the proper course here--connect the #12 wires using wire nuts in a small box (not attached to the wall)? – Jim Stewart Apr 16 '18 at 9:42
  • The very fact that it is attached to a plug rather than a permanent connection inside a junction or device box means that it will be flexed, i.e. every time it is plugged or unplugged. Your expectations may be that this will be infrequent, but since it is possible it must be allowed for. – mickeyf Apr 16 '18 at 11:52
  • Jim Stewart…I did not make clear that this was for a dishwasher that was previously installed in my original question. Though in my comments I did establish that it was installed four years ago. Therefore there won’t be any moving around of the dishwasher (with subsequent flexing of the cord) until one day in the future when it gets replaced. But when it does get replaced, the dishwasher power should be turned off at the breaker box first. – MJCallinall Apr 21 '18 at 17:21
  • @MJCallinall: Just because you're not actually removing it and plugging it back in doesn't mean it's not flexing, wire expands and contracts as it heats up. Regardless, it's against code for multiple reasons, so just do it right instead of looking for reasons to do it wrong. – GManNickG Apr 24 '18 at 1:34

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