I'm attempting to replace some switches and have opened up two of the boxes in my bathroom. I've found that for all the switches (5 total switches in 2 different boxes) they only use black wires.

In one of the boxes, there are 4 distinct sheathed groups of wires, which each sheath containing 3 wires: black, white, and copper. All 4 of the white wires are joined into a single wire nut, as are all 4 of the copper wires plus an additional one screwed into the back of the box. The other box is the same (but only has 2 switches and 3 sheathed bundles).


I am super perplexed by this setup. When I test for continuity I get it between some of the black wires in one box and in the other box, as well as between some combos of wires within a single box. One of my switches even has a wire jumping between it and another switch (see photos).

note jumper at bottom of closer switch If necessary I can try to draw a continuity diagram. Part of the reason I started working on this was because I had one switch that needed to be jiggled to work, but if jiggled the right way, it would turn OFF a light that is controlled by a switch in the other box.

So here are my questions:

  1. Is this correct/safe
  2. How is this even working when it seems like it's only using hot wires making one big circuit. Why aren't any white/neutral wires used?
  3. Should I use the ground wires for new switches that have ground connections, and if so, do they need to be matched with the sheathed bundle that has each switch's black wire, or are they all going to the same place.
  4. How can I add a timer switch that has red, green, black, and white connections (load, ground, hot, neutral). (See photos)

New timer switch enter image description here

  • 2
    The wires to a switch are black because they are both on the "hot" side of the light that is being controlled. Imagine a light connected to power without a switch. There will be a white neutral wire and a black hot one. Now where do we put the switch? The safest thing is to splice it into the hot one: snip the black wire.
    – Kaz
    Dec 30, 2019 at 17:49
  • 1
    Finally, a wiring question where the job at hand isn't a complete mess.
    – bishop
    Dec 31, 2019 at 2:38

6 Answers 6


Yes, this is correct. In fact this is the preferred way to wire light switches.

One cable brings ground, neutral, and live in, live goes to the switch then a different cable takes live, neutral, and ground up to the light socket.

The white neutral wires are not connected to the switches because mechanical switches do not need electric power to operate.

for the new switches connect the ground wire to the copper wires. the copper wires should also connect firmly to the metal electrical box, there should be a green screw. all grounds go to the same place, so allways connect all grounds together.

The white wire should connect to the white neutral wires in that wire nut.

The red and black will be a little tricky. the black goes to the black on the supply cable and the red to the black on the lamp cable, so you'll need to determine which is which. eg using a voltage detector.


North American wiring uses the following color codes:

  • green, yellow/grreen, bare -- ground
  • white, gray - neutral
  • all other colors - any hot
  • In 240V 3-phase delta, wild leg must be orange, but you'll never see that.

That is the sum total of color coding requirements in NEC.

As you can see, your boxes comply. Black is legal for any hot (except a wild leg). Cables are sold as black-white, and white is spoken for, that leaves black.

Your best recourse is marking wires

When you get a pack of colored electrical tape, the world is your oyster. Now, boxes start to make sense. Preferred colors are:

  • Black -- always-hot
  • Gray - alternate neutral
  • Yellow in pairs -- 3-way travelers
  • Blue in pairs -- alternate 3-way travelers
  • Red - switched-hot choice 1
  • Blue - switched-hot choice 2
  • Yellow (solitary) - switched-hot choice 3
  • whatever other colors come in your multi-pack of colored tape - choice 4 etc.

Note that white or green tape on a black wire does not, and cannot, make it a neutral or ground.

3-way circuits benefit especially from marking, as travelers tend to the two leftover colors after the common wire is selected.

Your questions

Is this correct/safe? The flaky connection is neither correct nor safe. The "goth" wiring scheme is totally legal, but not very maintainable obviously. I would never do it. I swerve out of my way to own 11 colors of wire!

Is it safe to use that smart switch you just bought? Depends on its certifications and how you sourced it. CE+Amazon Marketplace = nope. CSA with file number = fine.

How can this work, why aren't neutrals used? How it works will be more apparent once you color wires. The neutrals *most certainly are used! That's why they are spliced together instead of being called off individually! Remember, electricity travels in loops, it has to come back somehow. If you want to disconnect the neutrals for poops and giggles, you can see what breaks if you do. When you do that, beware - neutral wires become hot. That's in fact why they are insulated.

Should you use ground wires? Check if your ground wire bundle is attached to the steel box. If so, you get to use an exception for steel boxes for switches: they are allowed to ground via the metal box, mounting screws, and device yoke. The yoke is those metal wings that accept the mounting screws.

How do you wire up that device?

  1. check its provenance as described above. Gotta see that UL, CSA, ETL etc. listing with a file number, or back it goes.
  2. see if the yoke is metal. If it is, grounding is done and you can leave that wire dangle.
  3. do the color coding I mentioned above.
  4. Match up colors and yer done.
  • 3
    Can't tell for sure, but reading the part of the manual that is in the picture, it looks a lot better than standard Chinglish. So either it is legit. or it is a (relatively) good imitation. Dec 30, 2019 at 6:09
  • 2
    It's from Home Depot, hopefully Legit. @Harper thank you so much for the tips, I had a hard time choosing the "answer" but your info was exteremely helpful as well. Thank you so much for taking the time to respond!
    – jzadra
    Dec 31, 2019 at 1:40

I'm an electrician. Switches have two "hots" one is the switchleg (switch to light) the other is the line in. The whites are neutrals, possibly for the lights and nearby outlets. The bare copper is ground and will be tied to the box itself. If you have a voltage tester you will notice the switch legs are only hot when the switch in in the on position. At the light itself you will find the line in (switchleg) and a neutral running straight to panel. The switch itself does not need a neutral. All a switch does is break the hot wire to stop flow to the light.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. Jan 1, 2020 at 1:04

Ok let me start with the basics... wire conducts electricity regardless of the color surrounding it.

Standards are utilized so that we all understand what the wire in hand is doing... black(aka hot) comes from the power company... shouldn't have but often does have a load ( energy consuming device upon it). White is the neutral (return the power to the power company line)... to add to the complexity of all this that ground... safety wire... will have and should have continuity with the neutral persuant to NEC code.

Details regarding this may be above the current level of discussion.

In staring at your picture I was sad and slightly disgusted that nobody mentioned a connection of stranded to solid wire. These connections MUST BE SECURE OR...FIRES...therefore it's a quality standard to convert stranded wire to a solid metal connection.

Other gripes... connections depend on the metals connected. Your old switches require copper....

It appears you have nice quality SOLID copper wire running in your house. The individual that wired it....not so quality... short cuts and stupid silly cost cutting appears to be their norm. No wonder you were jiggling switches(A version of electrical Russian roulette).

In that tone of cost cutting.... Your "new switch appears to be STRANDED aluminum..(yuck... it corrodes...heats up differently to copper...conducts differently and requires different connectors to join different metals together (translation pricier)) Even if it is copper wire in there the stuff is still stranded is also the issue of connections and crimping such connectors. So really not a savings just an added failure point.

Please get the house checked by a proper electrician.

  • The red is sometimes used to allow for three way switches... another switch to control the same light... such a switch requires a total of 4 wires between each switch.... and only three total to the light... the red is known as a traveler...in the case of fans.... it's used for the light (so you can still see without having a breeeze all the time you need light)
    – Otter
    Dec 31, 2019 at 2:17
  • 1
    new switch appears to be STRANDED aluminum - I highly doubt that. Stranded quite possible, aluminum unlikely. Nothing wrong with stranded as long as it is secured properly. Dec 31, 2019 at 2:25
  • 1
    Aluminum and CCA have never been used for fixture wire (or any finer strandings than Class C), AFAIK.... Dec 31, 2019 at 3:22

The switches that have jumper cables is just an old method of giving both switches power from a single wire. That is most likely your constant hot btw. All a switch does is break the hot into 2 so that it cant carry power. That means that you could theoretically have 100 switches on just one wire if you kept daisy chaining them lol i dont recommend that.


Ok for your timer. Black in your powersource from the panel. Red is your load, or the object you want to time for instance an outdoor security light. White is your neutral wire. Green/bare copper is your groundimg wire. This keeps you amd your equipment safe. Without a ground wire if you make contact with Hot/neutral or hot/ground or a neutral with a load your breaker will not pop and you will keep getting buzzed. Its recommended to turn off the breaker and keeps ground wires together while you work. By no meams should you attach a neutral to the box or groumd as this is illegal in some states. Attaching a neutral to ground will liven up all that metal with 120/240/480, you name it.

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