PME earth

[Odd-no-more]

Hi any sparks here that can offer advice on the earth for EHU. I'm putting in an outdoor socket for hook up. The bungalow has a PME earth, and I am unsure if this is suitable for hook up. It has an RCD and I could put in an earth rod and connect that socket as a TT, would that be better?

 

[Mikeco]

My external wall mounted EHU socket has a normal 3 pin plug at the end inside the bungalow and is plugged in to a socket in the pantry, cannot see why you need anything special.

 

[andy63]

I'm not an electrician.. But is a pme earth not your normal earthing.. Ie utilizing the board earth and bonding the neutral..
If that is the case then connecting up the ehu to a socket on that type of supply would be fine..
Preferable to trying to install earth rods..
Andy

 

[kevntrace]

same here,put an external socket on the garage wall,cable goes through the wall with a 3-pin plug on the end,protected by the house fuse box.

My external wall mounted EHU socket has a normal 3 pin plug at the end inside the bungalow and is plugged in to a socket in the pantry, cannot see why you need anything special.

 

[Odd-no-more]

It's a while since I did my electrical training, but I have a vague memory about the safety of PME earth system for caravan and MoHo. But I am not sure

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[Silver-Fox]

I’m no electrician but I would of thought providing your not drawing more than 13amps your home ring main would be ok.

This is presuming you have a more recent consumer unit with trips.

I have an outside socket that runs off our ring main ?

 

[M-J]

I’m pretty sure regulations state that a camping/touring site cannot offer EHU when they are on a PME system, not sure why but there must be a reason.

 

[Odd-no-more]

I’m no electrician but I would of thought providing your not drawing more than 13amps your home ring main would be ok.

This is presuming you have a more recent consumer unit with trips.

I have an outside socket that runs off our ring main ?

It is not about the power it is the type of earth, a PME earth relies on the neutral being earthed before it enters the property and is shared with nearby properties. I do remember from my training a PME earth is not suitable for a swimming pool or wet area and I have an idea it should not be used for caravan etc. but it is a long time since I did the part P course ,and after I did it all I ever did was wire up heating controls so I was hoping we had a qualified electrician on here who could advise me

 

[Silver-Fox]

It is not about the power it is the type of earth, a PME earth relies on the neutral being earthed before it enters the property and is shared with nearby properties. I do remember from my training a PME earth is not suitable for a swimming pool or wet area and I have an idea it should not be used for caravan etc. but it is a long time since I did the part P course ,and after I did it all I ever did was wire up heating controls so I was hoping we had a qualified electrician on her who could advise me

I agree a sparky would be handy.
Yes I appreciate your not worried about the amps.
But I’ve plugged into many 13 amp sockets without issue ?

 

[63720]

This is not a recommendation as my qualifications are out of date, I'm not advising you to do anything!
In principle once you have connected an ehu lead to your M/H you have created a big portable appliance that needs to be plugged in somewhere. PME was used before the advent of RCDs which are sensitive to the imbalance of current drawn between the live and neutral conductors and isolates the supply if some goes missing ie through you to earth! I cannot see this changing during the connection and use of a van to a socket. I believe the warning about caravans refer to static vans for permanent residence. Also if your van has had a regular habitation inspection the electrical system will have been inspected and the internal circuit breakers tested for correct operation. In PME installations the earth and neutral are bonded near to the incomming mains and again at the transformer down the road. This was used when many properties were supplied with 2 wire overhead cabling. If I'm worng then someone will hopefully put me, and you, right.

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[Odd-no-more]

Thanks I have had a quick Google and there seems some doubt about PME. I have never worried before, and since we moved in I have used the socket I put in for the lawnmower, for ECU when I have used hook up with no problem. The socket I'm putting in now is for ECU only and as such I want to so it right, so I've ordered an earth rod and clamp from Amazon and will have some fun hammering it in next week.
It may not be needed as there is doubt as to the risk,which may be theoretical or real,but there is no risk with a TT earth, so I feel happier with that.

 

[Vipar]

Be careful of the drainage pipes or worse the loo sewer?

 

[Odd-no-more]

The drain is to the rear and electric is overhead, it's just the water main to worry about and of course the gas

 

[Canyon904]

Hi any sparks here that can offer advice on the earth for EHU. I'm putting in an outdoor socket for hook up. The bungalow has a PME earth, and I am unsure if this is suitable for hook up. It has an RCD and I could put in an earth rod and connect that socket as a TT, would that be better?

Is there any metal or other earthed locally parts that could be touched if the van faulted live to chassis? Is the van on wet grass or tarmac/concrete? I would go TT but I'm not part 'P'

 

[hilldweller]

Where is pappajohn when you need him ?

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[bigwood]

The earth side of this matter is not something I can comment on but the socket on our drive for hook up or hedge trimming is wired as per instructions from the electrician that re-wired our house.
We have one socket at the bottom of the stairs on the outer wall. It has its own trip separate from the rest of the house. He said drill through the back and wire the outside socket into the back of the inside socket. He recommended a waterproof socket with a cover.
If the electrician did this it would involve all kinds of regulations because the socket was outside. If the house ever has to be sold the socket may have to be disconnected along with the wiring for my shed and workshop but I will worry about that at the time.

 

[TinaLes]

Been a few years, and terminology & test certificates have changed, but still very basic.
Here you go, all you need to know about the 3 different wiring methods used by electric suppliers in the UK.
You will need an earth loop impedance tester to test the impedance from the earth rod if you fit one,as ground conditions vary so much, and of course a 30ma RCD protected waterproof socket, ideally with a separate switch fuse at the home incoming mains end.
The crucial bit after identifying your supply type is mentioned at 17 mins on the video.
LES

 

[Odd-no-more]

I have fitted earth rod before and I have my test equipment albeit out of calibration. This is going to be the safe option.

 

[DBK]

My understanding of PME is the neutral and earth are effectively the same wire inside the house. When you plug the MH into such a system you now have a giant appliance sitting on rubber tyres on the drive. If within the MH the earth is connected to the vehicle chassis then in a PME system this is the same as the neutral being connected to the chassis.
If there is a local phase/load imbalance this could mean the MH chassis could register a voltage between it and the ground. It is very unlikely to be a high voltage but might be say 40 volts. Probably unwise to lick the MH in such circumstances.

 

[Rob Turner]

No PME for farms, petrol forecourts, swimming pools and caravan/touring parks are the main ones. Ideally a TT system is preferred but a TNS is acceptable.
You’ll probably have PME at home and then a TT system on a campsite. I wouldn’t worry too much.

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[Odd-no-more]

I have PME and no problem with that, I don't intend to change the earth to the whole property, only the new socket for hook up, partly because the consumer unit does not have a RCD I have replaced the mcb's with rcbo's but not on the lightning so a TT system would be sub standard for this.

 

[Rob Turner]

I have PME and no problem with that, I don't intend to change the earth to the whole property, only the new socket for hook up, partly because the consumer unit does not have a RCD I have replaced the mcb's with rcbo's but not on the lightning so a TT system would be sub standard for this.

Can’t you fit a RCD

 

[dabhand]

I wouldn’t worry too much, I ran my farm (PME Earth) with a 6” nail as a main fuse for years, no problems sank a ” normal” earth as well, Because the supply neutral is bonded to earth in a PME system, the fault return path for both line to earth and line to neutral faults is via the combined conductor. The advantage of using the combined conductor in this way is that it provides a low impedance return path which ensures rapid disconnection of the supply under fault conditions. BUT, I’m no expert, not had a problem in 21 years though

 

[Rob Turner]

I wouldn’t worry too much, I ran my farm (PME Earth) with a 6” nail as a main fuse for years, no problems sank a ” normal” earth as well, Because the supply neutral is bonded to earth in a PME system, the fault return path for both line to earth and line to neutral faults is via the combined conductor. The advantage of using the combined conductor in this way is that it provides a low impedance return path which ensures rapid disconnection of the supply under fault conditions. BUT, I’m no expert, not had a problem in 21 years though

I work for the Electricity Board and had a fault at a farm that was PME!!

We don’t know how it was PME because it should have be TT but the customers earth was bonded to our neutral block which WE wouldn’t have done.

This would have been like that for years and fine until a fault on the o/h network occurred!! The blue phase on the overhead line clashed with the neutral (return) wire, thus sending supply voltage down the neutral and made all the steel work on the farm LIVE!!
The farm system was quite old and had no protection which didn’t help.

This killed cattle that were leaning against the steelwork at the time it happened and continued to stay live until the linesmen arrived and pulled substation fuses.
The farmer raised the alarm when he himself had a belt from touching one of the deceased cows, it could have been a lot worse!!


This is why we don’t PME farms!!

 

[Odd-no-more]

Can’t you fit a RCD

I could, but the consumer unit is not split, so it would take everything off if it tripped, that is why I fitted rcbo's I would have to replace the consumer unit to do it right, and I am not registered or qualified to do it. A PME earth is fine in the bungalow, it is how all new properties are supplied, it is just not recommended for hook up.

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[Sandancers]

Don't forget that in any oldish house your incoming water pipe may well be lead and this will be bonded to the earth block in the house. So whichever system of earthing you have got will also have a lovely earth rod made of many metres of lead.

 

[Odd-no-more]

Don't forget that in any oldish house your incoming water pipe may well be lead and this will be bonded to the earth block in the house. So whichever system of earthing you have got will also have a lovely earth rod made of many metres of lead.

It is lead and I have bonded it in 10mm, so you're right, if I had remembered that I may not have ordered the earth rod. Too late now.

 

[Rob Turner]

It is lead and I have bonded it in 10mm, so you're right, if I had remembered that I may not have ordered the earth rod. Too late now.

Never presume anything!
it could be alkathene just before it comes in the property.
Always test!

 

[dabhand]

I work for the Electricity Board and had a fault at a farm that was PME!!

We don’t know how it was PME because it should have be TT but the customers earth was bonded to our neutral block which WE wouldn’t have done.

This would have been like that for years and fine until a fault on the o/h network occurred!! The blue phase on the overhead line clashed with the neutral (return) wire, thus sending supply voltage down the neutral and made all the steel work on the farm LIVE!!
The farm system was quite old and had no protection which didn’t help.

This killed cattle that were leaning against the steelwork at the time it happened and continued to stay live until the linesmen arrived and pulled substation fuses.
The farmer raised the alarm when he himself had a belt from touching one of the deceased cows, it could have been a lot worse!!


This is why we don’t PME farms!!

An unusual set of circumstances, sounds like a bodge up of the farms installation as well.

 

[Rob Turner]

An unusual set of circumstances, sounds like a bodge up of the farms installation as well.

A cheap way of gaining an earth, until the inevitable.

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