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My existing wiring has 2 black and 2 white and a ground. One pair is obviously source. The 2nd pair passes to the next outlet.

The current outlet has 4 screws: black on one side and white on the other.

Now I need an outlet with USB ports, so I selected the Leviton t5633-w because of its high USB amperage.

It only has 1 set of screws.

Can I add a short piece say 4-6 inches to the black and the white so I can connect it to the single set of screws?

Therefore there would be 3 black wires wire nutted together, and 3 white.

Physically, it's clear I can do this. However, what does the US National Electrical Code say?

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    The one to look out for is (usually) white one side, black and red the other - a sign of an MWBC, where both hots cannot connect to a single screw as there's 240V between them. Or else a half-switched outlet. Or just pay attention to if the hot side tab between screws is intact, or broken off (intentionally.) If the tab is there, nutting them with a pigtail won't cause problems.
    – Ecnerwal
    Sep 12 at 16:36
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    I hate in-wall USB power. No matter how high you go in amperage and capabilities, the next phone you buy will need even more. QC, QC2, QC3, PD. That Leviton you chose will not charge ANY of my devices as fast as they are capable of being charged with the right charger. It's actually not a very good USB charger at all. 15W per outlet max. A 15W PD outlet is a joke. Do yourself a favor, put in a regular AC outlet and buy good chargers.
    – jay613
    Sep 14 at 12:19
  • @jay613 Well I know that these outlets ONLY provide 5v and not the other voltages expected by the PD,QC, or etc. However, I just have a 5v 1000ma device so rather than using an outlet strip for 1 more device I am doing this. Also the other outlets are not close enough. Only someone who doesn't know any better would expect to quick charge their phone or tablet this way. Sadly this is a lot of people.
    – cybernard
    Sep 14 at 14:38
  • @jay613 you wait, future houses will have 00 gauge wiring at 20v from a central PSU to USB outlets in every room :-) No electrician required, unless they change the wiring code after shorts burn down houses.
    – Rich
    Sep 15 at 2:05
  • @Rich That doesn't make electricians enough labor money, you will need a whole separate circuit breaker box for 20v with dual wiring all over your house. Each outlet will have 2 set of wires one for 20v and one for 120/240 or etc.
    – cybernard
    Sep 15 at 12:16
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Adding the short wire is called pigtails and it is code compliant so yes you can do this.

Pigtails are a superior way of making connections in my opinion. The pigtails do not add to the wire volume in the box.

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    Or rather, they don't add to the calculated wire volume in the box.
    – Ecnerwal
    Sep 12 at 16:33
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    Gotta agree with Ed, once again. In fact pigtailing is the best practice for all outlets. At least the one you removed was using the screws and not the backstab connections. + Sep 12 at 19:04
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    Pigtails don't come undone by itself unless something massively stupid was done, like you yanking on the wires. Screws can actually come loose over time, but it is still much better than backstabs, which are guaranteed to come loose.
    – Nelson
    Sep 13 at 2:18
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    @Nelson A properly made pigtail will not come apart even if you pull on the wires. In fact, you should be giving the wires a good pull-test to make sure the pigtail is solid and won't come apart like this. Screws will also not come loose over time unless they weren't properly torqued to begin with. Making electrical connections is not foolproof - it has to be done correctly. If it's done poorly, it can fall apart. If it's done well, it won't.
    – J...
    Sep 13 at 11:42
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The most important rule in NEC is 110.3(B), which requires you to follow labeling and instructions... which means read them.

In this case, that only makes things better, particularly the boldface in 4a and 4b. These explain how to use Leviton's "back-wire" feature, which allows placing 2 wires under each screw.

Pay heed to the word "FIRMLY". You really need to torque it like you mean it. You can tell if it's not tight enough, the wires won't pass a "pull test".

However, Code only requires you read and follow those instructions, it doesn't require you to use that splice technique. If you want to use a pigtail and can correctly execute it, that is fine.

Remember to give a very firm "pull test" on the wire nut splices (hold the nut and pull each wire in turn, hard - if it pulls out that's a technique problem: refine). And never, ever use tape on wire nuts to keep wires from falling out - that sets the stage for an arc fault creating a house fire.

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    +1 I really wish manufacturers would start making people use 110.14(D). I mean, they even put a torque spec (14-18 in-lbs) for the side-wire configuration. The least they could do is give a torque spec for the backwire method as well. "Torque it like you mean it" always makes me cringe. For some people it's still not going to be enough. For the rest, it means stretched bolts and stripped lugs. I'd go with the side-wire guidance and aim for the high side of 14-18 in-lbs in, personally. A torque wrench is never a bad idea.
    – J...
    Sep 13 at 15:23
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    I think this should be the accepted answer. Fewer points of failure means that the homeowner doesn't try to contrive a pigtail which relies on the holding power of electrical tape.
    – MonkeyZeus
    Sep 13 at 19:10
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    @MonkeyZeus How do pigtails require electrical tape? I certainly didn't use any. I am depending on the holding power of wire nuts. In a sealed environment, that a person opens maybe once every 5 years maybe.
    – cybernard
    Sep 14 at 14:43
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    @cybernard Zeus is suggesting that pigtails can be more likely to fail simply because the homeowner who tasks themselves with constructing one may not be aware of the correct way to do it and may therefore concoct some sort of DIY pigtail splice made with tape or some such - had they not tried to swim out of their depth, in this case, and just used the backwire clamps instead we therefore avoid the situation of an untrained person potentially producing a substandard splice.
    – J...
    Sep 14 at 15:54
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    @cybernard Glad to hear you don't rely on electrical tape for pigtails! This page will be visited by thousands of people long after you've gotten use from this community.
    – MonkeyZeus
    Sep 14 at 16:27

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