Replacing receptacles - why are white and black wires crossed?

Question

I am in the process of replacing all receptacles and wall plates in my home. Most of the receptacles are pretty straight forward to replace as they have only one black and one white wire (and ground). Now, I am running into a couple receptacles that have two black and two white wires (and ground). Sometimes the white and black wires are coming from the same corner of the receptacle, sometimes they are crossed.

How should I re-wire them?

Should I also cross them in the replacement receptacle?

What is the reason behind cross wiring (if that is the right term to use)?

Per request, I added the sides of the receptacle:

Answer 1

Indeed they are crossed.

It doesn't matter because the linking tabs are intact

So, electrically it makes no difference, both left screws do the same thing, both right screws do the same other thing. and so top and bottom are interchangeable.

When you replace the outlets you should probably wire one romex to the top outlets and the other to the bottom, if for not other reason than to reduce future confusion.

Answer 2

Check the tabs.

Check the tabs. That is the #1 trouble spot. If a tab is broken off on the old receptacle, do the same with the new.

When there are 2 wires on a side, what that means is totally different if the tabs are broken off, versus not.

White wires on silver screws, black on brass screws

The old one should be like that. If you see a case where it is not, take some good photos of the back of the box and both sides of the receptacle, and ask a new question. Because there might be something special going on there.

What you call "crossing" should simply be the wires getting to where they belong.

If you have been disregarding this, and "uncrossing" the wires, then you need to go back and correct that. In those cases the outlet will probably function normally, but will create an electrocution risk situation.

If the tabs are not broken off, then the wires simply need to obey the above rule: you can swap two whites on two silver screws if that fits better.

If the tabs are broken off, then position also matters.

While you're in there, ground the receptacle

The one in your photo is grounded. If you find any that are not, get some #12 bare wire, and some wire nuts, and run a pigtail from the group of grounds to the receptacle.

If you can't ground, then have a conversation with someone knowledgeable about GFCI protection (don't simply slap in a GFCI receptacle in every location; but if you insist on doing so, only use the LINE terminals and leave the warning tape on the LOAD terminals).

On switches, screw color is vital, and wire color is unhelpful.

I gather you'll be doing switches too? In switches, wire colors are almost meaningless. In 1-way switches (2 screws only), it doesn't matter. However, 3-way and 4-way switches absolutely require care in matching wires to screw colors. I like to mark travelers with yellow tape. Travelers are on yellow screws in 3-ways. On 4-ways, one pair is on yellow, the other pair is on black.

Answer 3

First question is - are any of the outlets switched? Also, if any are switched, and technically even if they aren't, its important to be sure that each outlet is controlled by only one circuit breaker.

For the most part you should find the answer to be yes, but its still a really great idea to confirm it, especially since you aren't the person who wired it in the first place. Then you'll have a diagram, and in the event you do end up having any problems, you'll know what outlets and lights and appliances are on what breakers.

So please; do this homework in advance. Your future self will thank you.

Next question, why are you changing them? Do you just want a different color? is there something wrong with them? Also, is any of your wiring aluminum? If so, let us know because there are other things you should be doing.

With that out of the way, looking at the photo you posted, it looks like these outlets are "Screw Clamp" - thats a great thing. But there is another type known as a "quick lock" aka "Backstab" connection which is cheap cheap cheap and quite dangerous. And they look a lot like what you have pictured.

Examples: https://www.handymanhowto.com/electrical-outlets-side-wire-versus-back-wire/

Please read that page, they did a great job of explaining the difference and the danger. The takeaway for you is to NOT USE BACKSTABS for any wiring you do. Do not do it on anything for any reason. Again, your future self will thank you (so will your family and neighbors).

Here is another great read for you, and it addresses the first two questions I asked, mainly being, if you have a switched outlet, or somehow one outlet which is fed by more than one part of a circuit (which is extremely dangerous btw), you need to use breakways for the latter and fix the issue for the former:

https://inspectapedia.com/electric/Electrical_Outlet_Split_Connections.php

Now I'll answer your questions:

1. How should I re-wire them?

Exactly the same way they are already. There should be no reason to change how it is wired at all. Unless of course they used backstabs, which, at no point should you use them, and if the outlets you bought have backstabs, then you should use the side screws. You will put all black to HOT (small slot) and all white to NEUTRAL (big slot). ONE wire per screw. Ground goes to chassis.

2. Should I also cross them in the replacement receptacle?

When you say "should I cross them?" Well, you should follow my answer to #1, accented by all the material given to read as homework. If you mean should you have the wires criss-cross around each other in the back, the real answer here, is to just keep the wires untangled, and run them so that when you go to put the outlet back on and screw it down, it will do so without pinching the wires, or causing any sharp bends or folds or kinks. Many times what you see done is the wire is tucked into the back of the box "top to bottom" behind the outlet, and when the box is shallow, or crowded, you'll see it crossed over and tucked into the sides. The point is, dont pinch or cram the outlet back in against the wire. Dont damange the sheathing. And don't trim the wire so that bare copper is hanging out of the outlet past the screw or back-lock hole.

Keep it clean and tidy.

3. What is the reason behind cross wiring (if that is the right term to use)?

Explained in #2.

Answer 4

The first thing to check is to see if the metal tabs on the sides are broken off or still intact (I cannot tell from your photo). If one or both are broken off, then the two receptacles are powered separately (maybe one is switched). In this case, you must wire the new unit the same way and break off the same tab(s).

If the tabs are intact, then both wires on a side are internally connected together and you can connect them either way without making a difference. This is typically used to continue power onto another receptacle down the line.

As noted in the answer by @noybman, you should avoid using the backstabs on the new outlet, unless they are clamped down by the screw.

Answer 5

The reason for the criss crossing of the wiring is to allow electricians to quickly identify faulty receptacles. In this method, if the receptacle experiences a short or becomes faulty, the 120v link through the outlet would be broken. Some receptacles short externally, some internally. This method quickly identifies the problem. It became un popular once gfcis began being used as they have a very specific input and output to work properly. As long as the joining tabs are intact just keep the grounded conductor on the silver screws and the ungrounded (colored) conductors on the brass screws. All will be good