I had had a “moment” a couple of weeks ago.

A socket circuit had blown its wire fuse in an old BS3036 fuse board, because it was in a very poor condition, there’s a double pole 30 mA RCD upfront of the fuse board. Having completed a couple of repairs to the circuit I replaced the blown fuse with a spare plug-in MCB out of my van, then did a loop test and an RCD test.

With the installation “isolated” by the double pole RCD that I had tripped with my Megger MFT1741 I reset the tester to do a loop test on a different socket and check polarity, but it displayed 98 volts and went into one of those diagnostic apps sequences where it indicates voltages between different conductors.

I had missed isolating the PV that feeds into the installation downstream of the DP RCD, I didn’t try to determine if it was phantom voltage, but I doubt it was, I got the power back on scribbled some comments about recommendations to upgrade the existing installation on the MWC and got out of there.

I have had odd voltage readings before in installations with PV, yes if you isolate the PV and the mains there isn’t any voltage, but if you put it into tripped after a fault condition then you can get odd voltage measurements.

Having said that the worst I have experienced was a PV and battery installation where the installers had installed a four pole switch as a dual supply isolator that disconnected the installation live, but livened up the neutral, so the installation appeared to be dead but both the line and neutral had 240 volts on them, as well as the live and neutral bars in the consumer unit, because the neutral was being back fed then the live was back fed through the connected appliances.

https://www.tlc-direct.co.uk/Products/WYNHDSREC4.html

There are actually some scary PV installations out there.

I had had a “moment” a couple of weeks ago.

A socket circuit had blown its wire fuse in an old BS3036 fuse board, because it was in a very poor condition, there’s a double pole 30 mA RCD upfront of the fuse board. Having completed a couple of repairs to the circuit I replaced the blown fuse with a spare plug-in MCB out of my van, then did a loop test and an RCD test.

With the installation “isolated” by the double pole RCD that I had tripped with my Megger MFT1741 I reset the tester to do a loop test on a different socket and check polarity, but it displayed 98 volts and went into one of those diagnostic apps sequences where it indicates voltages between different conductors.

I had missed isolating the PV that feeds into the installation downstream of the DP RCD, I didn’t try to determine if it was phantom voltage, but I doubt it was, I got the power back on scribbled some comments about recommendations to upgrade the existing installation on the MWC and got out of there.

I have had odd voltage readings before in installations with PV, yes if you isolate the PV and the mains there isn’t any voltage, but if you put it into tripped after a fault condition then you can get odd voltage measurements.

Having said that the worst I have experienced was a PV and battery installation where the installers had installed a four pole switch as a dual supply isolator that disconnected the installation live, but livened up the neutral, so the installation appeared to be dead but both the line and neutral had 240 volts on them, as well as the live and neutral bars in the consumer unit, because the neutral was being back fed then the live was back fed through the connected appliances.

https://www.tlc-direct.co.uk/Products/WYNHDSREC4.html

There are actually some scary PV installations out there.

When electrons were more of a novelty and voltages more variable and a domestic generator needed fossil fuel,  you often found moving coil meters  built into or beside the private genset to give a visible indication of generation - partly I suspect to impress the natives and justify the price but hey ho..

Thinking about the problems of being certain that things with multiple sources are really on or not, with sources that do not make helpful chugging noises or create smoke to indicate generation in progress, that  perhaps now, given that  digital volt meter modules have never been cheaper, it might be a good idea to have something with an LED display or similar to show that the inverter really is inverting, or failing that a pilot light in or beside the CU. - actually I've thought that before with off peak supplies as well , that a little neon light to show that the cheap rate is on or not would have not cost very much as part of the CU .

Mike.

Well said that man!