Just got a condo, trying to switch out the wall outlets to something new with USB ports. I'm a little confused by the wiring and YouTube hasn't quite shown any examples with what I'm seeing. Located in the USA.

I generally gather that 3 pronged outlets should have a hot, a neutral and a ground wire.

When I open the outlet I see a red wire, a black wire and two white wires. Is red hot, black neutral and the white wires ground? Do I need to "pigtail" the two white wires into one?

My new outlet has only 3 connections for hot neutral and ground.

Full outlet Two white wires

Further more opened up one of the switches and found what I assume to be the ground wire just attached to the electrical box. Is this a hazard? (green wire)

Picture below:

Hazard? From box to switch?

  • Black and red are hot; white is neutral. Be very careful: you may well be in over your head. Commented Mar 3, 2022 at 22:24
  • The two white neutrals are connected(same as pigtailed) at the outlet. Noticce that little tab between the screws. Is that tab on the hot(black and red) side? If not then the top and bottom are separated.
    – crip659
    Commented Mar 3, 2022 at 22:24
  • 1
    Frame challenge: Do you really want to replace $30 outlets every time USB standards change? TBH, I thought about installing USB outlets as well at one point, but there have been at least 2 significant changes in USB standards (2.0 -> 3.0, changes in wattage delivered, USB 3.1 and USB-C). Each of those changes would have required new outlets. Instead, I just use the brick supplied with new devices and pick up a couple of cheapie chargers supporting the latest standards that will plug into any standard wall outlet anywhere in the US...
    – FreeMan
    Commented Mar 4, 2022 at 13:14

1 Answer 1


You probably have a half-switched receptacle. The image showing the Red & Black side isn't clear, but it looks like it may have a broken tab.

Half-switched receptacle wiring diagram

If you can safely figure out which wire (red or black) is hot and which is switched hot, you can cap the switched one with a wire nut and connect the other to your receptacle. Taping or leaving a note would be good to help yourself later or the next owner figure out why the light switch appears to do nothing.

On the ground (green) wire, it should be connected to the box via a screw and not just wound around the box. The receptacle should have a similar ground wire there too - when metal boxes are used, they must be connected to ground.

Disclaimer 1: If this sounds difficult, you may want to get a professional to help replace this receptacle. Some jurisdictions don't allow anyone except licensed professionals do electrical work, and messing with this if you're not comfortable can cause property damage or kill you.

Disclaimer 2: There are various reasons why replacing a receptacle with USB variants is a bad idea. First, many of these you can buy off the Internet are cheap junk that originates overseas. These are not safe to use and are likely to burn out (hopefully safely) and stop working. Second, USB charging standards move pretty quickly and what works well today will be obsolete in a year or two. USB-C is a current standard for charging, but cables and chargers are constantly updating wattage to support newer quickcharge standards. Swapping out a charger brick is simple. Swapping out a receptacle is less simple.

Related article re: switched receptacles

Related article re: USB receptacle

Related article re: USB part of receptacle dying

  • 1
    Could also be an MWBC....
    – Ecnerwal
    Commented Mar 3, 2022 at 22:53
  • 2
    There's a complication. Code requires that at least one light switch in the usual location operate a lamp or a receptacle you'd plug a lamp into. If that is the only switch, and the only receptacle controlled by that switch, then it must be switched. A USB outlet would remove the ability to have an unswitched half, it would have to be all switched. Commented Mar 4, 2022 at 3:38
  • To be clear, this is the tab on the neutral side of the outlet. Is that missing from the hot side (where the red & black wires are)?
    – FreeMan
    Commented Mar 4, 2022 at 13:20
  • Is there a spare white wire in the switch box? I suspect there isn't. My guess would be these are older than 2011, and since a switch loop wouldn't have required a neutral then only a two wire loop would've been required. So since 3 wire is present it seems likely to me or at least possible that the switches for these receptacles are ahead of the receptacles as shown here do-it-yourself-help.com/images/… Commented Mar 4, 2022 at 15:11
  • There is a bundle of whites in the switch box, see photo 3. Commented Mar 4, 2022 at 15:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.