Update. To those who insert 2 wire to each terminal or 4 wires to the breakers, and just increase the torque to compensate for it. What torques did you use (did you increase it?). My 10-50 in-lbs torque screwdriver (with certification) finally arrived.

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If there are two wires inserted in one breaker terminal. What must be the torque for say two AWG 10 wires? Must it be 20 in-lbs or 25 in-lbs (based on the following breaker in the picture). What do you think?

Getting the desired torque is very important to be sure the two wires and terminal lugs should have conduction at least equal to the wire original area.

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original message:

Given a 30A breaker and AWG 10 wires. What is the problem if you insert 2 pcs of AWG 10 to each terminal (hence 4 wires for each breaker)? I'm not asking about current and protection by breaker or capacity as I have taken all these into account already, But I'm just asking what is technically wrong with inserting 2 wires in each terminal (when the breaker doesn't have any listing about it). Remember as long as the terminal is screwed tight, there would be full electrical contacts between them and no arcing, heating, right? What can possibly go wrong?

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  • What are you trying to do? Where are the wires going? – Tom Feb 15 '19 at 10:04

There are breakers made with a lug that can accommodate two wires, but most breaker lugs will only take one wire. You may get away with stacking two wires - it may not fail or burn up - but sometimes it does. It's not a reliable way to make a solid connection.

You can easily pigtail the two wires - splice them to a third short wire of the same gauge - the pigtail - and terminate the other end of the pigtail on the breaker lug. So it's pointless to take a chance doubling up.

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  • What do you mean sometimes it does burn up or fail. How can it burn up if the two AWG 10 are very tightly secured in the terminal? I don't want to pigtail them because there is no reliable way to connect the two to one. Wire nut is not stable. It's better to plug them in direct to the terminal. – Jtl Feb 15 '19 at 10:50
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    I'll take a properly made wire nut connection over an improperly made breaker lug connection any day. Your situation: your speculation is at odds with others' experience, the manufacturer's engineers (and in most places) the electrical code. Good advice: in such situations, distrust your own speculation, study the situation further, and wait until you develop a great deal of experience before doing things your own way. – batsplatsterson Feb 15 '19 at 11:12
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    Properly installed wire nuts make an excellent splice, but some proficiency is required, and if you don't feel fully confident in your wire nut connections, you should splice with another method. However you should not make up your own method or misuse another connection - that's a step in the opposite direction. Find a compliant method that you're comfortable with. – batsplatsterson Feb 15 '19 at 11:53
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    "it can could catch fire in future", and so can two wires in a breaker lug designed for only one wire. if you worry that your wire nuts are not holding, then get better at using wire nuts. also, there's a reason that electric systems are typically in metal enclosures: shorts to the enclosure usually result in tripping a breaker, eliminating fire risk. – longneck Feb 15 '19 at 14:34
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    With #10 you'll need a red or tan wire nut, and really show it who's boss when tightening. With 3 #10 you've got it about right if your fingers hurt afterwards. Then do a "tug test" afterwards. Wire nuts are excellent splices, but they are vulnerable to bad technique. – Harper - Reinstate Monica Feb 15 '19 at 17:06

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