I know that’s why I don’t think it’s a dead short and the reading is from the USB points, live to earth IR test, goes down the earth which is also connected to the neutral at the supply TNCS will go through this neutral back around all socket and through the line conductor hence giving me a short circuit, but when line and neutral connected together all clear ??
But regarding the USB sockets. If I have not disconnected the neutrals from neutral bar and tested between live and earth and I am getting low reading basically zero near enough, this should be because the USB points are bringing the reading down as I will be going through the earth and being TNCS will be linked to neutral so will be testing the USB point. As when I link out live and neutrals at the consumer unit and go to a socket then test live to earth insulation resistance it comes out clear. >999mega ohms. Now if that was a damaged cable that would be picked up, does that make sense ?
It should also be noted that the electronic circuitry inside the SMPS could easily be damaged by a 500 V insulation test injected across it. Consequently the USB port may fail to function following a 500 V Line to Neutral insulation test
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