I have worked a lot with reduced low voltage and in some cases the volt drop has been silly. But trying to think of danger due to excessive volt drop is hard. With some thing like a fan heater one could have the fan stall and so the unit could over heat but it would need to be an extreme case and there should be an internal thermal fuse which should rupture if that was to happen.
I have seen shrink rap machines fail to work correctly due to volt drop, but there was no danger it just did not work, and with the reduced low voltage I had problems with fluorescent lights both drawing excess current when voltage a little on high side and not striking when on the low side and yes being plunged into darkness could be considered as a danger.
But it does depend on where and what is supplied. When working on the tunnel boring machine in Hong Kong it was instant dismissal if caught down the tunnel without your personal head lamp. There was no reliance on the mains powered lighting. But in Sizewell 'B' the tunnels were lit with reduced low voltage and there was no emergency lighting or a requirement to carry even a touch.
With switch mode or pulse width modulated units the volt drop on lighting can be huge before there is a problem I fitted a R7S LED replacement rated 85~265 volt however the PIR is unlikely to work at those limits, but it shows how by selecting the lighting the problem of volt drop can be avoided.
Earth loop impedance with a RCD can be very high, as to the neutral - line loop impedance I have seen arguments both ways as to if it needs to be low enough to operate the magnetic part of the trip. I have seen consumer units with type C RCBO's for all circuits, seems with some makes it is hard to find type B and I have questioned if it complies? We have seen a reduction in the loop impedance of 5% it is claimed to allow for volt drop and yes I can see the argument however it really does depend on the meter. I had a Seaward meter which if you compared the loop impedance and the prospective short circuit current it clearly worked on the assumption that we had 240 volt. Where I worked we had step down transformers for the tower cranes 415 to 380 volt so we had some 220 volt single phase to some items like radio chargers which were supplied from the auto transformer what we did not know was if the PSCC or the loop impedance was correct?
The meter accuracy was also debated as to volt drop. We can measure the supply impedance and the impedance at the point of use say 0.35Ω and 0.94Ω and use the formula given in the BS7671 and compensate the volt drop figures giving 16.52 mV/A/m instead of 18 mV/A/m using the correction factor of 0.92 and show with maths that the volt drop is 11.5 volt and the cable length for the ring is 106 meters. However if the meter is just 0.01Ω out then it all goes to pot. I spent ages on this forum testing out my Java Script program and some faults were found and corrected
JohnW2 and
EFLImpudence both helped sort out the problems.
However once done then it was the accuracy of the measuring equipment which proved the problem. One can hardly with an EICR say that the installation was incorrectly planned unless the readings are really blatantly out of spec getting a reading of 0.35Ω and 1.44Ω with a ring final start and centre reading one can be reasonably sure it is over the volt drop permitted. But even then it would depend on the design current used, I was told at an IET meeting we should use 26 amp for a ring final that's assuming 20 amp at centre and the remaining 12 even spread, however I can't find anything written down to say that.
So as the designer I am free to take 13 amps at centre and 19 amp even spread so I could work on 22.5 amp which would allow 1.03Ω instead of 0.94Ω with that in mind how would one show the design was flawed? The reverse is true with using 32A at centre.
So for an example a garden shed requires wiring, the wiring is designed to allow the lawn mower to be plugged in, no lighting, the lawn mower was 750W so 3A but to allow for start load that's a bit too small of a fuse so the preferred size of 13A is used but never the less the design current is 3A. If at a latter date lights are added and the shed is used to brew beer in that's beside the point, the design current was 3A.
So with an EICR how do you say the design was incorrect rather than the use was incorrect? You can't.
So for my shed even if there are lights as long as the ELI is within limits I don't care if the volt drop is OTT as I know my LED lamps will still work, but with a customers shed I do need to consider volt drop as I can't control what they use. As an in house electrician again I can ignore the volt drop because I can control what is being used. Sockets come as 16A, 32A, and 63A so if I want to supply a 17A machine I can fit a 32A socket and yet design current is still 17A.
As an electrician we have to make that call. It is no good hiding behind a regulations book, this is the real world and it does not take 4 years to learn a reg book, you need to use the skills you have and design using those skills. Yes to talk to peers is good, it helps us tune our skills over the years, but as BAS so many times has said, it is your signature on the paperwork you have to decide in the end no one else.
