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It is common knowledge that wires should be color-coded. In a single-phase system, the colors mark phase, neutral and ground. However, installing a switch and some appliance, I am going to have the following:

  • From the supply to a switch -- phase (always-hot).
  • From the switch to an appliance -- phase (switched-hot).
  • From the appliance back to the supply -- neutral and ground.

So, I run a two-wire cable from a junction box to the switch, and a three-wire cable from the junction box to the appliance. My question is about the color-coding in the cable that runs to the switch. If I use a standard cable with wires colored as phase and neutral, than what actually is switched-hot (which in the junction box is connected to the phase wire of the appliance-heading cable) will be colored as neutral, which might cause a confusion. What is the proper way?

Should I use a different cable, where wires would be of the same color, to run to the switch? That would add hassle, because cables are easier to buy and use in bulk.
Should I stick colored tape to the wires as another answer suggests?

For the sake of avoiding region specifics, let's not mention any particular colors. For the same reason, please try to avoid referring to state-specific regulations unless they provide useful insight from the common-sense perspective: consider my motivation to be just the convenience of my future self.

Alex Serenko
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  • Your local rules & regulations can't be ignored in answering this question. In the US, if you have a switch loop where you're repurposing the white (neutral) wire in a cable you have to use that as the "always hot" and the black (hot) as the switched hot. It may be different in other jurisdictions. If you're using individual wires in conduit, it would be different. Use of "phase" indicates you're not in the US, though. Please [edit] your post to be more specific. – FreeMan Mar 15 '22 at 13:26
  • Usually only have to worry about marking/changing wires if using a switch loop, one single /2 cable to a switch, where neutral is used as phased/hot/live, and dark(non green/bare) is used for switch hot/phased/live. Using two or more cables or single /3, colours maintain their use. – crip659 Mar 15 '22 at 13:26
  • Where you in the world? The North America has a standard that has recently been updated but there are exceptions switch loops and 3 way switching are common examples where the “neutral” may be a current carrying conductor. – Ed Beal Mar 15 '22 at 15:25
  • If it is absolutely necessary for the question, I am in Russia, so European regulations apply. (However inappropriate it may seem to think about wiring now, I still hope my house outlives the dictatorship.) My (rather typical) situation may well be covered in the rules; sorry if this is the case. Then please consider my question as asking for a layman-friendly explanation of such rules. – Alex Serenko Mar 15 '22 at 15:44
  • @crip659's comment seems quite close to an answer. – Alex Serenko Mar 15 '22 at 15:45
  • What route will the wiring take from end-to-end? Will it run from the supply, past the appliance, to the switch, or will it run from the supply, past the switch, to the appliance? Either way is fine, but it'll determine whether or not you have a "switch loop" in your wiring. – brhans Mar 15 '22 at 21:17
  • Yes, @brhans, I am going to have a switch loop like here, which was the whole point of my question. Thank you for pointing me to the right term to call it! – Alex Serenko Mar 16 '22 at 12:20
  • I am now considering flagging my question as a duplicate of that one. @crip659, do you think the answers to that question apply to mine? – Alex Serenko Mar 16 '22 at 12:20
  • Wire colours and number of phases(wires) are usually region specific. The answer you linked to is specific to North America(black and white, split phase) and has been changed in recent years, but can still be used in older homes. Russia and Europe has different electrical systems and might not use the way to make switch loops/circuits. – crip659 Mar 16 '22 at 13:00

1 Answers1

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So, think of it as that you have 3 nodes: Power source, switch and lamp. (or whatever).

Make a diagram of the physical topology of your planned wiring route. Now, we need to connect 4 wires:

  • Protective Earth - from source to all points.
  • Neutral - from source to all points.
  • "Always-live/hot" (live when utility power available): Goes from power source to switch.
  • "Switched-live/hot" (live when lamp is desired to be on): Goes from switch to lamp.

Once it's on paper, you will see that some places require 3-wire (2 wire + earth) wire. And other places may require 4-wire (3-wire + earth) wire. This will vary depending on the wiring topology of the installation.

You need to use the wire colors required by your regional authorities. This is important so "the next guy" working on your electrical can figure out the work.

Even though neutral is not strictly required by plain switches, it is needed for smart switches, and as such, many jurisdictions are requiring neutral be brought to switches. It's just a smart idea even if it's not required; but it's hard to know if it's required because gosh, 11 years after it was mandated in North America, many online educational sources still give the obsolete advice.

Countries universally have standard colors for Protective Earth and Neutral) that are required by law.

The colors for "live" wires are less strongly established (except that they can't be neutral or earth colors)... but there will be a preferential color for "always-live" (usually the color of the first phase), and often a preferred color for "switched-live" as well.

Harper - Reinstate Monica
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  • Indeed, running neutral and ground to a switch would make reusing a standard-colored cable for a switch loop impossible, which would render my question obsolete. However, it still looks like too much hassle for too unlikely future need. – Alex Serenko Mar 16 '22 at 15:15
  • @Alex I'd expect all cables contain a ground/earth. Presumably the default 3-core cables contain both the neutral and the primary live color, as well as the secondary live color... so it's not really a problem. I recommend doing it even if you think the application is "unlikely". The cost is minimal compared to the cost of rework later. Also your local code may require it! There's never a need to go more than 3 in "2-way" multi-switch control, because smart switches can get that done in 3. – Harper - Reinstate Monica Mar 16 '22 at 18:07