I need to combine two wires with very light room lighting loads into one breaker in the panel to free up one breaker for another use. How best to combine the two wires and insert only one into the breaker (since the two can't fit)?

  • This has a practical and a legal aspect. For the practical, see the existing answers. For the legal, it is important where you live. The question should tell us this. – Stig Hemmer Jan 25 '19 at 11:08

You can simply pigtail them in the panel - splice those two wires to a short third wire (pigtail) of the same gauge and type, and land the other end of the short wire on the breaker.

Wire nuts are most commonly used for splices, but they do take some skill to use successfully. Push in wire connectors are also commonly available, and are much easier to get right on your first attempt. In either case, you must be very careful to select connectors compatible with your wiring. In particular, be very careful if there's any aluminum wiring involved.

There is a persistent myth that the NEC prohibits splices in panels, but there's really no such rule.

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    @jtl - wire nuts are not messy but there is some skill involved. Wire nuts come in all different sizes, you can easily find wire nuts rated for three #10. Are you sure these are #10 wires? Are they copper or aluminum? Be very careful if there's any aluminum involved, especially if there is a a mix of copper and aluminum. I would strongly suggest you not attempt soldering in any event. – batsplatsterson Jan 24 '19 at 14:56
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    Soldering is completely unnecessary and probably increases risk of a failed connection. It's not something that's done for house wiring, partly because the conductors are large enough that a typical soldering iron or gun won't do the job well. Wire nuts are nearly foolproof if you're paying attention, and they can be easily removed and reinstalled if needed. – isherwood Jan 24 '19 at 15:07
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    @jtl - soldering is still technically allowed in the NEC but it's not forgiving at all, and may not be accepted by an inspector. Different techniques are required for power compared to what's commonly done with electronics. – batsplatsterson Jan 24 '19 at 15:09
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    @Jtl - It has been discovered that solder eventually breaks down due to corrosion and dissimilar material causing electrolysis. So it is not recommended for house wiring voltage and amperage. It causes a high resistance splice creating a burn or shock hazard. The wirenut is still the best way to go, unless you want to set up some short of terminal block. Just select the right size wirenut. – Retired Master Electrician Jan 24 '19 at 16:10
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    @jtl because wirenuts (or mini lugs/Alumiconns) are reliable, easy wiring methods that have stood the test of time, whereas soldering mains has a very particular method that is required by the rules, and proper execution is a lost art. A significant part of that is the insulation. I'm glad soldering works for you in your electronics projects where you're flowing 300ma, but mains soldering is a whole 'nother ballpark. You'll have to redo it anyway at inspection or house sale time, no inspector will sign off on something that weird. – Harper - Reinstate Monica Jan 24 '19 at 16:16

You can also check the manufacturer of the circuit breaker to see if it is listed to have two wires per lug. Not all of them are, but there are a few very common brands that allow it. Square D QO series breakers for example are UL listed for two wires per terminal.

(I am assuming from the wording of your other posts that you are in North America somewhere so that the Square D brand name is relevant).

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  • For those not listed. What is wrong technically with having two wires per lug? – Jtl Jan 28 '19 at 6:13

Also can you wire nuts three awg 10 together? Wont they get so thick? – Jtl

Are you unaware that wire nuts come in different sizes? There is a size for three #10 copper wires, e.g., Scotchlok (tm) G (the grey ones).

EDIT The listed sizes and numbers of wires to fit in a given wire nut does not take into account the thickening from "pre-twisting", i.e., the listed sizes and number of wires for a given wire nut presumes that the wire ends are just held parallel and the wire nut is twisted on until it is on hard tight.

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  • So pre-twisting is not necessary and just add to the thickening requiring even bigger wire nuts? – Jtl Jan 24 '19 at 23:38
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    Pretwisting copper wires is definitely not necessary. It can result in a set of wires not properly fitting in a wire nut if the pretwisting expands the diameter of the bundle of wires above what the wire nut is designed for. If the diameter of the properly pretwisted bundle of wires is below the limit for the connector, then it will not hurt and might conceivably help to make a connection last longer. I never pretwist because I'm not confident I have the training and experience to do it properly. – Jim Stewart Jan 24 '19 at 23:57
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    @JimStewart - IMO if the instructions allow 3 #10s and instruct allow pretwisting, then it will fit fine pre-twisted. Keep in mind that the steel insert in the nut is a spring, and that the wires will twist in the process of twisting on the nut. – batsplatsterson Jan 26 '19 at 10:51
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    My idea on this is old and may be no longer correct. I was told this 35 years ago by a trouble shooting electrician from a major electrical contractor in Dallas. I was of course aware that as one twists on a nut on a set of parallel ends that the wires twist somewhat inside the nut. It may be that the mfgrs of the nuts have changed their specs or even the design of the nuts because so many electricians were in the habit of pre-twisting. – Jim Stewart Jan 26 '19 at 13:24

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