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As far as I've seen, two-terminal AC power cords connected to mains are always packed together (hot and neutral wire in one cord or next to each other). I'm also no electrical engineer or anything, but I was just wondering this:

What happens if we run the wires from a socket to some arbitrary device but split apart the hot and neutral wire? After splitting, recombining the wires at the devices again. So let's say the cables are split for the length of 1 meter from socket to the device and are individually insulated. Also, let's assume the current is 0.5A, and the voltage is 230V, and the frequency is 50Hz.

Does splitting the hot and neutral wires from each other create magnetic fields that would be problematic for nearby electronics? Would it be a safety hazard?

And lastly, (I wouldn't say it would be handy but just for the sake of the example) would it be legal?

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  • \$\begingroup\$ I would think there would be a minor safety issue here: If the return is separate it could become disconnected separately. You would then have a device that was apparently unpowered but was actually hot and could prove a danger to someone touching the wrong spot. \$\endgroup\$
    – Loren Pechtel
    Aug 6, 2021 at 4:19
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    \$\begingroup\$ The DIY Stack Exchange talks a LOT about code and would be able to answer the “is it legal” part of your question. \$\endgroup\$
    – Reid
    Aug 6, 2021 at 21:05
  • \$\begingroup\$ Related issue: If you're running power wires from point A to point B in metal conduit, the electrical code says you must have the hot and neutral physically in the same conduit. Otherwise -- if you ran the hot wire down one conduit, and the neutral back along the other -- you'd create a transformer, inducing current in the metal conduit. (If you have high current needs, meaning you physically can't fit both wires in a reasonably-sized conduit, you're supposed to use multiple smaller wires, in parallel, but with the same number of hots and neutrals in each parallel conduit.) \$\endgroup\$
    – Steve Summit
    Aug 7, 2021 at 16:16

2 Answers 2

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Does splitting the hot and neutral wires from each other create magnetic fields?

Not the way you mean. Each wire will have a magnetic field. With the wires close together, the magnetic fields of the wires will be close together, of the same magnitude, and in mostly opposite direction, so they'll mostly cancel out.

Basically the circuit is a loop, and the more area the loop has, the more the resulting magnetic field is coupled to free space. Put another way -- the more you space the wires out, up to about a wavelength or so of your power line frequency, the better an antenna you're making.

that would be problematic for nearby electronics?

Only sensitive electronics.

Would it be a safety hazard?

It would at least double the tripping hazard, and increase the chances that the cord would get tangled and yanked out of a plug, thereby creating an electrical hazard.

And lastly, (I wouldn't say it would be handy but just for the sake of the example) would it be legal?

"Is it legal" always depends on the jurisdiction you're talking about -- and it's really not for this group. But I'm pretty sure that if you had one in your house and someone told the cops, no one would come knocking at the door. I'm pretty sure that if you invited your local fire officials to your home for a safety inspection (if they do that where you live) then they'd tell you not to do that. And, at least under US (and probably British, and perhaps even most European legal systems) if you have a significantly non-standard cord and a fire starts in that room, the insurance company will use it as an excuse to not pay for your fire damage.

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  • \$\begingroup\$ Just to add: often (but of course not always) "separate cables" means a pair of single-insulated wires. Under the electrical code of many jurisdictions mains conductors are required to be double-insulated, for safety. \$\endgroup\$
    – Keeley Hoek
    Aug 6, 2021 at 6:44
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    \$\begingroup\$ I understand this to be the reason why "splitter cables" (of the kind to which the OP refers) can be hard to come by, though they could potentially serve a legitimate purpose e.g. for easy use of a current clamp on an AC line. Often manufacturers adopt a different form factor for such splitting devices, instead of a cable. \$\endgroup\$
    – Keeley Hoek
    Aug 6, 2021 at 6:47
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    \$\begingroup\$ "Sensitive electronics" would include electric guitars with single-coil pickups, at least when the pickup selector is used to select one coil. \$\endgroup\$
    – supercat
    Aug 6, 2021 at 20:49
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Basically that's what generic holiday season lamps already do - or used to when they were just regular light bulbs in series. So it must be legal.

From mains plug goes one single wire to first lamp and so on until from the last lamp the wire goes back to mains plug.

Hardly a safety hazard - at least in case of shop bought light string. And yes the loop area is huge compared to case where Live and Neutral wires go tightly packed side by side from plug to device. Most likely not able to cause too much magnetic field to disturb other electronics.

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    \$\begingroup\$ For some clarification here. I believe @Justme is referring to the lights where the cord splits immediately out the back of the mains plug to a string of small incandescent lights, rather than the strings that accept standard mains bulbs (and are usually supplied with various bulb colours). I don't think you can get the former anymore (in AU). \$\endgroup\$
    – toxicantidote
    Aug 5, 2021 at 23:41
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    \$\begingroup\$ The more modern decorative lights run off of DC (usually 24v) and will usually have groups of LEDs in series (i.e. group of ~8, in parallel with another group ~8) That way they keep a 'safe' voltage, but save money by not needing thick wire to handle the current of having them all in parallel. For multi coloured lights, the 'groups' are usually one colour, with members of other colour groups between them. This is why you will see several wires along the string of modern LED lights. \$\endgroup\$
    – toxicantidote
    Aug 5, 2021 at 23:44
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    \$\begingroup\$ The light strings I've seen always packed both (or more, when dealing with groups of blinking lights) wires together. The hot voltage drops after every lamp, but the neutral return is still there with it. \$\endgroup\$
    – Loren Pechtel
    Aug 6, 2021 at 4:18
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    \$\begingroup\$ At least in the UK, I remember both styles, a loop was cheaper to make but less conviniant to use. \$\endgroup\$
    – Peter Green
    Aug 6, 2021 at 19:58
  • \$\begingroup\$ @PeterGreen yeah, you had to use special technique - start with the middle 2 bulbs, place them on the top of the tree and from there work both wires down synchronously in order to end up with useable length to a socket : ) \$\endgroup\$
    – Agent_L
    Aug 7, 2021 at 14:37

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