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Is there a particular connector to use on 10AWG copper wire?

I want to extending a 240V AC single phase dryer circuit with 10/3 cable (Note: "10/3" here in BC is 4 wires total: three 10AWG insulated solid strand, plus one uninsulated solid strand bare copper).

I’d make 4 pigtails in the existing outlet box. White, Red, Black, Bare/Ground.

I was practicing with the twist connectors I have on hand (Ideal-brand "fits-all" which should accommodate 3x10awg) but they really don’t work as well as they do on 14 gauge. The connectors are bulging, and the 10awg conductors barely change shape.

(I'm Trying to bring your attention to the visible plastic stress. Please ignore: (1) the colors , I just connected pieces from the same section of cable for a test. (2) the fact that this is not a pigtail per-se, but it's holding 3 conductors, the same amount that I would need to add a pigtail...)

twisted

If hold the wires in place, and remove the connector to inspect, I get this, barely any twist:

after twisting

Notes:

  • The instructions on the connector packaging state that pre-twisting is unnecessary.
  • My original dryer circuit is grounded to the main panel, and also 4 wires (red, white, black, bare) 10AWG.
  • I only have one dryer, and only one outlet will ever be used at any time. I could condemn one of the two outlets with a blank faceplate if there's not enough room in the outlet box (about 4"x4"x1.5" deep)

instructions

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  • Please ignore the colors, I didn't have three of the same lying around. The packaging does boast "one size fits all..." albeit poorly, apparently.
    – init_js
    Feb 7, 2023 at 3:34
  • I learned from my electrician that you should always pre twist before putting on the wire nut. Feb 7, 2023 at 5:25
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    Terminology: a wire-nut connection like you show here is not a "pig tail". A "pig tail" is a short (usually 6" or so) additional piece of wire you add to one of more existing wires, typically where you need to connect multiple wires to an outlet which only supports 1 wire on each terminal.
    – brhans
    Feb 7, 2023 at 13:17
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    @manassehkatz I don't think you should "always pretwist" solid copper wires before twisting on a wirenut. Done properly a pretwist may nearly always give a high quality and long lasting connection, but it does enlarge the set of wires and might put it outside the limits of the wire nut you are using. Also it requires more wire and sometimes there is not enough. I would just follow the instructions for the wire nut. Even 40 years ago when I pigtailed my aluminum house wire I did not pretwist the solid Al #12 and #10 (not enough wire). My connections have stood the test of time. Feb 7, 2023 at 22:00
  • @brhans Thanks, I just put three wires in that wire nut to simulate what I would need to do to have a pig tail. One from the feed, one to feed the other outlet, and one for the pigtail. I can edit if that's throwing readers off.
    – init_js
    Feb 8, 2023 at 0:23

3 Answers 3

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I’m extending a 240V AC single phase dryer circuit with 10-3 wire (3x 10AWG solid strand, with 1 unshielded solid ground). I was thinking i’d make 3 pig tails in the existing outlet box.

An ungrounded dryer circuit cannot be extended. * So I assume you have both a neutral and a ground arriving at the existing box (plus two hots). The ground is either the shell of the conduit or its wire is landing on a ground screw on the metal box?

Then sure - three pigtails for hot-hot-neutral and then tie the ground to another screw on the metal box.

* Groundless dryer connections are dangerous and I do not recommend their continued use. NFPA says those installed prior to 1996 are "grandfathered" (but not if they used 10/2 w/ground cable) but that's still playing with fire. They kill people annually, disproportionately children.

I was practicing with the twist connectors I have on hand (Ideal-brand "fits-all" which should accommodate 3x10awg)

I'm glad you're practicing first. Failing to use wire-nuts correctly causes a lot of series arcing burn-ups of wire nuts and potential fires.

There is no such thing as a "Fits All". Each size of wire-nut is UL-approved for specific combinations of wires. Here is Ideal's document on the subject. This can get a little weird - for instance the Ideal 76B is rated for 1-3 #10 wires, but at two different voltages (if 3 wires only 300V).

Now, a few pieces of advice on wire nuts.

First, it's really ... ideal ... to use wire nuts in the middle of their range. If one nut is 2-5 #10, well two #10 is on the small side for that nut but it's just right for three #10s. Whereas a nut made for 1-3 #10s is at the limit of its range for three #10s - go for the next larger size.

Second, the golden rule: Gorilla-tight, not monkey-tight. I know that's the opposite of the rule for everything else, but on wire nuts you maul the daylights out of that sucker. I would even get the Wing-Nut or Twister models as they are easier to grip. Do not use tools - you'll crack the nut.

Lastly, doing the wire nuts right is pointless if you then limp-wrist the screw torques on the socket. Recent science has shown screw torques matter bigtime - look at all the talk among EVers about cheap sockets getting hot - it's not the socket it's the lack of a torque wrench when they installed it. NEC 2014 requires setting torque correctly on any screw that specifies a torque. On flat blade screws it's kind of a pain - critical to select a bit that fits properly - but it's worth it.

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  • oops. I see how my post has been misleading. I meant 4 pigtails not 3. I will edit -- the bare copper would need a pigtail too. My Original circuit has: white, black, red, bare/ground, and is terminated in a 4 prong outlet. I wanted to connect the pigtails behind inside the original outlet box. Not sure which of your concerns still apply when it's 4 wire. I will need a recent copy of the Canadian Electrical Code , I didn't see anything specifically forbidding dryer circuits (maybe just 3-wire circuits)?
    – init_js
    Feb 7, 2023 at 3:48
  • Good tips on the wire nuts. I'll try with bigger ones. Usually with 14AWG, I can twist the wire nuts until the wires start twisting into each other, but 10awg offers quite a fight. The push connectors are tempting...
    – init_js
    Feb 7, 2023 at 3:51
  • @init_js OK corrected the 3-wire warning. Only ungrounded circuits cannot be extended. If the dryer circuit has both neutral and ground (possibly via metal conduit shell) then you can call it a "general use" 30A circuit and there is no limit to the number of receptacles on it. Heck, add one in the garage for EV charging lol. Just like 15-20A circuits you must use good judgment to not overload it. Feb 7, 2023 at 20:33
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    We like the lever-nuts if they'll take #10. Otherwise might I suggest the best connectors made for this sort of job: Alumiconns. They're basically lug connectors, like on your neutral bar. They need to be torqued to spec though. Feb 7, 2023 at 20:41
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Use lever nuts. I mean, sheesh.

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  • That is another option worth considering. On his last visit, my electrician expressed contempt towards them — citing they took more space than wire nuts, and had a tendency to open if they catch on something when you push em back in the box. So I thought I would gather different views. I did order some 10AWG "wago"s to try out.
    – init_js
    Feb 7, 2023 at 21:52
  • My experience set, so far, @init_js, is wiring in 2 boxes with Wagos, but I haven't had issues with them popping open. Maybe because I'm the homeowner, doing DIY, so I'm taking more time than a pro trying to get through the job as fast as possible to maximize profit.
    – FreeMan
    Feb 8, 2023 at 15:53
  • I do not advocate that experienced professionals switch from twist to lever nuts. That would create unnecessary cost and risk with no benefit. They can all be installed poorly, but inexperienced DIYers can master lever nuts very quickly and can nut anything together with two sizes of nut and one set of procedures. To illustrate, you have already figured out how to do what you want with lever nuts, you know one big gotcha, and you will get it right regardless of his contempt.
    – jay613
    Feb 8, 2023 at 17:55
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Instructions in your photo say:

...screw on until 2 twists are visible in the wires.

That is, visible twists outside the nut. If you've got 2 twists visible outside the nut, the bare ends inside will all be twisted. Although pre-twisting is not necessary, it makes it easier to get to the final amount of twisting. Your photo of blue nut on 3 wires is severely undertwisted - the wires sticking out have essentially no twists visible.

Here's a screencap from the manufacturer's video showing that the wires outside the nut need to be substantially twisted: enter image description here

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