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USB sockets, testing at 250 V, and writing it downWhat do you write when you drop to 250 V?

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You cannot always get behind a socket to bypass it. A socket with USB outlets is the common case — and new builds are fitting them as standard, so you will meet it constantly.

What you do, and what you record

Cannot bypass  ->  test the circuit at 250 V, live conductors joined, to earth

Then put it in the remarks, in words:
  "Downstairs ring tested at 250 V due to five sockets
   with USB outlets."
Why 250 V still gives you a usable reading. It is close to the 230 V nominal, so the result is near enough accurate — and it is low enough not to damage the device. You are not sacrificing much by dropping to it.

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