I am not certain that PEN conductors are more liable to failure than are phase conductors. arguably a greater cause for concern in view of the  likely serious consequences.

Open circuit phase conductor = some customers lose supply until repairs are done

Open circuit PEN  conductor = risk of dangerous shocks between earthed electrical equipment and the general mass of earth, Also risk of dangerous overvoltage on the lightest loaded phase, AND fire risk.if neutral current is diverted via paralell paths that are inadequate for this current.

Kelly Marie Angel said:

I know this subject has been done to death but why are the neutral/PEN conductors more likely to go open circuit than any of the phases? It seems to me there is some basic problem the way they are installed are they not tightened to the same degree as the phases?

Quite simply, because it's not usually an insulated conductor within the cable, but the outer 'armour' or some other conductive covering under the sheath.

There are different types of cable that have been used in LV PME distribution, the most problematic being aluminium tape-covered type where the aluminium corrodes after water gets under the sheath after it's been installed for some time.

More recently, it's become popular to use a cable with aluminium line conductors, surrounded by a copper "armour", the copper being used as the PEN conductor.

In places where it is four singles - like overhead, as noted it is not more prone to come undone - the problem is that is less likely to fail in a safe way and so less acceptable than 'a power cut' which is what happens when one phase drops - which is so common it is not counted as a significant event. lost PENs are supposed to be counted, at least recently.

Actually on the overheads of most DNOs the neutrals are double crimped and have slack loops that the phases do not, so that usually the phase goes twang first.  This is very deliberate so that the line can be declared 'PME ready'

The problem arises big time with the underground cables, which are more like 3 core coax, where the armour is the neutral - because when this gets wet (stones or roots damage the sheath, or at joints) the water soaks in from the outside first - then it is quite common the outer armour goes high resistance while the phase cores in their wax paper wrap have not yet rotted right through.. .

Mike,.

PS this doc describes the problem facing SSE https://ssenfuture.co.uk/wp-content/uploads/2021/12/311_SSEPD_NLR_LV_UG_CLEANFINAL_REDACTED.pdf

broadgage said:

I am not certain that PEN conductors are more liable to failure than are phase conductors. arguably a greater cause for concern in view of the  likely serious consequences.

Quite so: are there any data available?

If a line conductor fails, the supplied installations are suddenly without power and the DNO gets called. The line gets fixed and nobody gives it a second thought.

However, if the PEN is lost the electrons might be able to find their way back to the transformer via parallel paths, but in the meantime, as broadgauge says, a dangerous situation exists. If something then happens such as fire or a shock, everybody notices and observer bias may arise.

Yes, it would be interesting to know the rate of PEN or just N failures as opposed to L.

Thanks for the information I think I was under a false impression about the way faults on PEN/neutral happen I suppose I should apologise to the DNOs for my comments we learn something new every day!

Yes, it would be interesting to know the rate of PEN or just N failures as opposed to L.

The figures I've come across for PEN faults were in the region of 1 per day across the country, or once in a thousand years for an individual consumer (as one fault typically affects quite a few consumers). All averaged probabilities of course, nothing actually stopping you getting hit twice in the same week, if you're unlucky.

Not sure about line faults - when I had problems with my supply and frequented my local DNO's web site to report it, their map of the region was showing dozens of power loss incidents at any point in time. Not all will be due to LV line faults of course - HV faults and LV overloads will also contribute to disconnections (I suspect that shorts caused by damage to buried cables will contribute quite a lot too).

  - Andy.

I think Paul Meenan has some stats on PEN faults.  I am sure he is an IET memeber.  Might be worth connecting with him.