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I need to repair a splice inside an outdoor, 60 amp, NEMA 3R AC cutoff switch. The electrician had used a NSI Tork IT-4 to lengthen the #6 to reach the switch terminals (all within the box). Its on a 60 amp breaker.

As I don't have #6 or better wire, I liked to run a pair of #8 THWN or #10 solid splice point to the switch terminal (all within the box). Is this an acceptable practice?

The new splice would be a Morris 90612 or SR-2 splice/reducer and would be insulated with shrink tube and electrical tape - with #6 entering one side, and a pair of #10 or #8, possibly twisted, leaving the other.

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    Where in the world are you? At least in the US under NEC, paralleling wires like this is not permitted, and using a non-watertight enclosure outside is also not allowed. – Nate S - Reinstate Monica Apr 25 at 23:33
  • @NateStrickland -- there's a difference between "rainproof" (NEMA 3R, aka a typical outdoor box) and something that's actually watertight such as a NEMA 4X. – ThreePhaseEel Apr 25 at 23:41
  • @ThreePhaseEel, ah true, I was assuming that OP meant it was an indoor box used outdoors, but you're right, if they just meant rainproof, outdoor rated but not watertight, then yes that's fine. – Nate S - Reinstate Monica Apr 25 at 23:43
  • No. Get some #6 wire. You're not allowed to parallel like that, and none of the splices or terminations are rated for that. This is the kind of bodge job they find after this. – Harper - Reinstate Monica Apr 26 at 5:33
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    Just to make it clear paralleling is allowed but only with 1/0 or larger wire NEC 310.10.H.1, at my current home the shop someone had paralled 2 10-3 as a feeder to a sub panel , lucky for me they put it in conduit so it was easy to pull the non compliant wiring and pull in some thhn, as for your grounding if you install 2 they need at least 6 feet between them 250.53.A.3 – Ed Beal Apr 26 at 19:55
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You're not allowed to parallel wires smaller than 1/0 AWG (NEC 310.10). Further, paralleling requires special equipment on the supply-side, and special dual lugs on the load side. This equipment handles certain very serious problems that can arise with paralleling.

Not least, what happens if one of the two wires breaks or has a contact problem, and all the current is flowing on the other wire?

It's maybe not so bad since since your issue here is entirely contained inside a junction box... however, it's maybe not so hard to get some #6 wire.

If you must cheat this, use a single #8 wire and declare "inside the box" to be a 90C environment, 55A@90C rounding up to 60A. That's not legal either, but it's a better argument than paralleling. Then do replace it as soon as you can obtain some #6.

NFPA does a lot of thinking about electrical safety in writing the NEC. Many rules didn't make sense when I started, but do make sense now that I have some experience and have thought more about all the reasons. I have never found a rule that didn't make sense, both in terms of safety and finance.

An example is the "neutral on switch loops rule" -- it causes 50 cents worth of additional hardship at install time, and saves $200 of additional hardship (or a dangerous hack) when the homeowner wants to install a light switch.

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