(I am located in the US)

I'm taking apart a cable to use for AC in a project. When I stripped the ends, I saw the expected Black/White/Green colors to indicate hot/neutral/ground respectively. However just to be sure (before using the cable) I traced each with a multimeter. What I found was as below, however their positions on the plug are REVERSED from what I would expect to find in an AC plug in the USA. (As indicated in any number of the results from e.g. this Google Images search)

Am I correct, that I should be using this cable's BLACK wire for neutral, and it's WHITE wire for hot?

AC Power supply cable

  • \$\begingroup\$ Apart from your question a note on safety: I see you have tinned the ends of the stranded wires and I see the housing of a SMPS on the right. I assume this SMPS has screw terminals. If you put tinned wires into screw terminals make sure your fire insurance pays in case of gross negligence. \$\endgroup\$ – Ariser May 7 '18 at 7:25
  • \$\begingroup\$ @Ariser: "If you put tinned wires into screw terminals make sure your fire insurance pays in case of gross negligence." Can you be a bit more clear? The snark makes me unsure if this is a serious comment or not. I do plan to put these into screw terminals. I typically tin wires any time I strip them, out of habit. However if it poses a danger I'd really like to know. Should I not do that? Thanks. \$\endgroup\$ – loneboat May 7 '18 at 14:38
  • 3
    \$\begingroup\$ Tinned strands are exposed to a tightening force in a screw terminal. Under this force the typical soldering alloys start to creep until the force is reduced to zero. As soon as the force on the tin surface falls below certain levels, oxide layers can form and contact resistance rises sharply. It is a matter of time until the connection heats up significantly. I've seen a lot of old installations with burnt down breaker panels due to this effect. \$\endgroup\$ – Ariser May 7 '18 at 15:02
  • \$\begingroup\$ @Ariser: Thanks so much for point this out to me! I had no idea. \$\endgroup\$ – loneboat May 7 '18 at 15:04
  • \$\begingroup\$ The best way to prepare stranded wires for screw terminals are ferrules or crimp style terminals. It's easy and inexpensive. But if you don't have them it is even better to put the bare stranded wire into the terminal and apply moderate tightening force instead of tinning the ends. If you have spring loaded terminals, tinned ends can be used, too. The spring keeps the contact force on a sufficient level until the tin is completely displaced and contact is made with the copper. \$\endgroup\$ – Ariser May 7 '18 at 15:29

You're right, it appears to be backwards.

However, in practice, it doesn't really make all that much difference. Inside your equipment, you have to keep both line and neutral isolated from the ground connection anyway.

Even if your cable was wired correctly, there could be an error elsewhere in the mains wiring.

In other words, you have to treat both black and white as "equally dangerous".

  • \$\begingroup\$ Okay, thanks a bunch. Yeah. I try to treat them all equally dangerous. But I knew there was a difference between the two, so I wanted to get it right before I wired it up. Thanks! \$\endgroup\$ – loneboat May 6 '18 at 23:22

No. In the US, house wiring is almost always black for hot and white for neutral.

  • 2
    \$\begingroup\$ Right, that agrees with my understanding of what they should be. But in this case, I traced them with a multimeter (per the red arrows in the image) - and they seem to go to the wrong sides. \$\endgroup\$ – loneboat May 6 '18 at 23:16
  • \$\begingroup\$ This is not a good answer in terms of a Q&A-site like EE.SE. No good relation to the question and way too short. \$\endgroup\$ – Ariser May 7 '18 at 7:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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