9

I have a receptacle that was wired with the black on the top right side screw and the white wire on the bottom left screw. Why didn’t they just use either the two top screws or the bottom two screws? I want to add a wire off of this receptacle to add another receptacle in the series.

isherwood
  • 137,324
  • 8
  • 170
  • 404
Todd Hinz
  • 91
  • 2
  • Welcome. l've revised your title to ask about the wiring rather than the installer's mindset. Please take the [tour] and see the [help] so you know how to use this site. Feel free to revise further. – isherwood Feb 19 '24 at 15:57
  • Only time you use both screws is if you break the tab (either which one at a time doesn't mater). "Pass-through" violates code, as removal of that device would interrupt devices down the line. YOU MUST USE PIG TAILS. – Mazura Feb 19 '24 at 20:19
  • 3
    @Mazura That is only true for multi-wire branch circuits. NEC 300.13 (B) does not apply to simpler circuits that only use one side of the phase. – Moshe Katz Feb 19 '24 at 23:37
  • Side thought - it might be one of those "stylesheet" things that the electician or company always does. Like leaving slotted screws all in the vertical alignment, or using colour-coded wire-nuts, or how they route cables inside a switchboard. Such things are unimportant in the function, but consistency makes it neater. (comment because not an answer) – Criggie Feb 20 '24 at 01:29
  • @Mazura - which code are you referring to? OP doesn't quote a location, and what I think you are describing is normal in the UK, for one. – MikeB Feb 20 '24 at 08:26
  • @MikeB If it was in the UK, the wires would not have been black and white, as the OP describes. They typically use brown and blue (or possibly red/blue and black, if it was wired before 2004). I think that you might also be able to have white and black in South Africa, but I have never seen SA wiring in person, so I cannot confirm that. Black and white almost certainly means North America, so US code is a good guess. – Moshe Katz Feb 21 '24 at 20:56

2 Answers2

13

Why didn’t they just use either the two top screws or the bottom two screws?

There's no requirement to do so. If the tabs are not broken off, the terminals are equivalent.

I want to add a wire off of this receptacle to add another receptacle in the series.

Then use the other two screws.

Note that you're not required to wire outlets in a literal string. You can "tee" off an intermediate outlet, at which point yes, you would have 3 wires on each side. You handle that either by pigtailing, or by selecting "spec grade" receptacles whose screw-and-clamp method permits 2 wires under each screw, or 4 wires per side.

Harper - Reinstate Monica
  • 300,628
  • 26
  • 286
  • 734
  • When you use the receptacles with the screw-clamp plate, do you put two wires under each screw clamp plate and no wires hooked around the screw (directly under the screw head)? In this type are you even allowed to hook wires around the screw shaft? Is the only approved connection method to insert the straight ends of wires under the plate and then tighten the screw? Cannot see why anyone would choose to hook wires around the screw shaft but just want to know. – Jim Stewart Feb 19 '24 at 16:07
  • 3
    Please ask a whole new question, @JimStewart. You've been here long enough to know that... – FreeMan Feb 19 '24 at 18:04
  • 1
    @Jim I would follow the instructions and labeling per 110.3(B). UL decides that stuff, and for all I know, they may do different things on different sockets. I have mused about double-stacking both screw-and-clamp AND J-hook, giving 6 per side, but absent a UL-approved instruction I would not do it. – Harper - Reinstate Monica Feb 19 '24 at 18:37
  • @JimStewart generally yes, you can hook around the screw or use the back tab (side wire vs back wire), unless the manufacturer says not to or the device lacks the feature for it. For example https://blog.leviton.com/back-wiring-vs-side-wiring some people just feel screw hooks are superior, same as thinking twist nuts are better than wago lever nuts. – cde Feb 20 '24 at 03:58
12

The why is how they held the outlet in their hand when tightening the screw.

The two screws on each side are connected with a small metal tab between them, so which screw does not matter.

Adding another cable/black and white wire, just use the other screws. Turn the breaker off first.

Newer code requires the use of torque drivers on screws/connectors.

At the time, you can also change which wire is on top or bottom.

crip659
  • 24,171
  • 1
  • 30
  • 61