Lost neutral on PME consequences

marcuswareham · Mar 9, 2021

timhoward said:
I know exactly what you are saying, and I have no experience with the public distribution side but I wonder if it is three conductors coming together at that joint location in a resin joint, and a joint failure would also sever the ongoing PEN to the next joint.
On large private estates I've seen it done like this (and had to fix it after a mini-digger driver had a bad day!).

Yeah i hear ya, likewise I have no experience with anything on the DNO side etc.

I can see the joints to my house as its on the top of a pole at the end of my drive and I looks to be like i explained in my last post

marcuswareham · Mar 9, 2021

snowhead said:
50 or so houses were affected where my Son was living a few years ago, spread across all 3 phases.
It was a newish estate of around 50 or so houses and the Neutral connection failed where the estate was connected to the existing cable in the main road.
It cost Western Power tens of thousands to sort out the damage caused.

Flipping heck

Knowbody received a shock then?

snowhead · Mar 10, 2021

marcuswareham said:
Flipping heck

Knowbody received a shock then?

No deadly shocks.
But Daughter in law got a tingle from a socket screw when she unplugged her phone charger, whilst standing on a laminate wood floor laid on concrete.
It was the first indication of something being wrong, it was weekday during the morning and she was off on maternity leave.
She rang a few neighbours and they all said various items had stopped working during the morning, including someone's Plasma Tv that had stopped working with a puff of smoke out the top.

DPG · Mar 10, 2021

marcuswareham said:
I have always thought regulation 722.411.4.1 (iv) where protection from a PEN fault is by measuring the utilization voltage between L & N and then disconnecting all conductors if it is outside the range of 207v - 253v, as a bit of a cop-out and only really solving half the problem as it is possible to have a PEN fault and the voltage to remain within that range

I have been thinking however the as a PEN conductor has multiple electrodes along its length so a break in the PEN conductor should still ensure you are connected to one or more electrodes, but I guess the weakest points are the joints and in particular the joints where individual houses etc connect to the PEN conductor, So would it be the case that most PEN faults occur at a joint where it branches off to feed a house also the section to the house is very unlikely to have any electrodes on, but in this case as it is only one house affected the above 722.411.4.1(iv) would work in most cases (subject to extraneous parts which are bonded), so is this why it is accepted as a way to mitigate PEN faults as in most cases it will protect due to the above

Attached is a crap picture to show the joints I am trying to convey

I think this is where a lot of the problems occur. It has happened on my estate more than twice. One was at my house where my cable is tapped off the cables running down the street under the pavement.

First we knew of it was when I used the hoover on the garage and it was struggling a bit. I put this down to it being a bit old initially. Then a couple of days later my wife got a tingle from the metal clad light switch in the garage. I got straight on to them and to be fair they ca.e out within a couple of hours from what I remember. They put a temporary feed across my drive from next door's cut-out until the jointers came and repaired things.

The jointers told me it's fairly common, especially with 1970s era housing.

marcuswareham · Mar 10, 2021

Iv just seen this video

so perhaps joint failure as i mentioned will be less of a concern in the future, although i exspect for now there there is plenty of old bad joints

pc1966 · Mar 10, 2021

marcuswareham said:
so perhaps joint failure as i mentioned will be less of a concern in the future, although i exspect for now there there is plenty of old bad joints

That bit of joint work was impressive, certainly gives some confidence in new installs. Full marks to the engineer who did that work for the video example.

But those are not the problem I suspect!

Same with the proposed building earth under the proposed 18th Amendment 2, great for now stuff, not really dealing with the last 30 odd years of deployment.

marcuswareham · Mar 19, 2021

Just seen a picture of an older PME joint

Apparently the copper "pigtail" in the left of the frame is a PME electrode, I wonder what kind of resistance that has, doesnt look like it has much surface area to be in contact with earth.

marcuswareham · Mar 19, 2021

I have been told by someone from the DNO fixing a power cut that this is a PME electrode at the bottom of a service pole in my village, At least my PME looks to have a much better electrodes that the last post with the underground joint. It seems as if every pole with a joint in my village has an electrode (not a joint to someones house, A joint in the main run)

LastManOnline · Mar 20, 2021

marcuswareham said:
I have been told by someone from the DNO fixing a power cut that this is a PME electrode at the bottom of a service pole in my village, At least my PME looks to have a much better electrodes that the last post with the underground joint. It seems as if every pole with a joint in my village has an electrode (not a joint to someones house, A joint in the main run)

View attachment 83493

Well exhibit "B" (from your village) definitely inspires more confidence than exhibit "A" (pigtail). But regardless TNC-S remains the black sheep of the electrical family. There is still no practical means of testing the effectiveness of the DNO,s PME rods. If a homeowner was to ask me tomorrow "How protected am I under an open PEN fault?", probably the best indicator you can give is the physical distance the home is located in relation to the DNO, s distribution trafo

marcuswareham · Mar 30, 2021

Another interesting PME electrode, rod just chucked in the hole

Lost neutral on PME consequences

marcuswareham

marcuswareham

snowhead

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DPG

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marcuswareham

pc1966

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