I got a USB wall socket fitted. When it was installed, I tested the USB port with a tester with the switches off, but the USB outlet was live. Is this normal?

  • 2
    Hello, and welcome to Home Improvement. It's hard to understand your question; would you edit it to clarify? (Some punctuation would be great...) Apr 9, 2019 at 15:03
  • 8
    Could you please provide the actual switch/outlet you used.
    – Ben
    Apr 9, 2019 at 16:34
  • 4
    This can only be a UK question. Apr 10, 2019 at 0:39
  • 4
    @Harper How can you be so sure? From what I can tell, "outlet" is quite an unusual word in the UK. Apr 10, 2019 at 8:11
  • 3
    I'm surprised a question with so little background information has 12 upvotes already!
    – Bort
    Apr 10, 2019 at 20:02

2 Answers 2


In the US, no the USB ports will not have power when the outlet is not powered. Most outlets in the US don't have power switches on them, so if you switch them off there is no way for power to be provided.
US typical USB outlet

In the UK, outlets often have power switches. In that case, your USB ports are usually powered while the outlet switches are off. This is because the outlet assembly itself is always powered, but the switches only control the outlet and not the USB power transformer.

    UK typical USB outlet

You said cheers in your original post, so I'm assuming you're probably British and have the UK type of USB outlet. Yes, this is normal.

Other answers are assuming that you are in the US, where that wouldn't be normal.

  • Unless the entire outlet is on a switched spur. where switching off the spur would turn off the USB (and the outlets regardless of the switches on the outlet) Apr 10, 2019 at 8:16
  • 2
    That's a correct description of the UK situation. I've just removed one and while it was off the wall I measured the power consumption of the USB charger: 2W with nothing plugged in and the switches off
    – Chris H
    Apr 10, 2019 at 8:35
  • 1
    @Rich exactly, it takes some power to even know whether there's anything there to charge. The maximum output of the one pictured would be about 15W (mine 10W). That's one of the reasons I took mine out, and I don't like having stuff I can't turn off easily.
    – Chris H
    Apr 10, 2019 at 9:14
  • 1
    @ChrisH thanks for the explanation. It's a shame there isn't a physical switch to control the USB ports, either like the ones for the plugs or one that is activated by something being inserted into the USB socket.
    – Rich
    Apr 10, 2019 at 9:57
  • 2
    @Rich you and I would prefer a switch, but it adds cost and I guess many people want the convenience of just plugging in the USB. I doubt you could switch the mains side with something operated by inserting a plug, because mains switches require a certain amount of material and therefore force to be robust enough, but switching the 5V side by insertion wouldn't help as the power supply would be idling as it is now.
    – Chris H
    Apr 10, 2019 at 10:53

Sometimes power supplies/transformers can hold voltage in capacitors to make it look like they are on for a short time after they are unplugged. Rather than checking with a tester, plug a phone (or anything that actually consumes power) into the charger and operate the switch to see if it is still on when the switch is off.

It's not impossible for the USB portion to have power all the time, but I've never seen a USB receptacle that would allow for it in the US.

edit: UK outlets can have integrated switches where this is much more plausible. See the other answer for the UK...

  • 1
    I have the British type as shown in Dotes' answer. I'm trying the experiment and so far it is charging my phone perfectly well with both switches off. I'll look in a few minutes but I'm pretty sure no capacitors are doing the charging. Apr 9, 2019 at 21:02
  • 1
    @chaslyfromUK, that makes sense. Our receptacles are different in the US and don't have integrated switches like that so it would be hard for this to happen. The UK based answer is right, but I'm leaving this answer because it can explain why voltages or small led lights stay on even after a charger is unplugged or switched off.
    – JPhi1618
    Apr 9, 2019 at 21:04
  • 2
    Update - Yes, completely charged my phone from 80% to 100% while mains sockets switched off. Apr 10, 2019 at 8:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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