Fixing TT earthing problems and gas bonding for an EV charger

[securespark]

Incidentally there is a very old earthing connector with the frayed remnants of a cable attached to it on a water pipe near to the CU so my guess is that sometime in this house's 100 year history the water pipes were the earth.

Possibly.
The other explanation could be that the GPO attached a wire to the water pipe to use as an earth for the telephone line. Back in the day, it was used for a shared service or for lightning protection.

You could, if you wanted, use the water pipe - or other metal parts except gas pipes - as part of the bonding conductor itself which makes a mockery of the claims that it must be a continuous cable.

Probably not the first time that BS documents are not in agreement.

 

[StuB]

Possibly.
The other explanation could be that the GPO attached a wire to the water pipe to use as an earth for the telephone line. Back in the day, it was used for a shared service or for lightning protection.



Probably not the first time that BS documents are not in agreement.

Everyday day is a school day, just some more than others.

 

[securespark]

Me too, you never stop learning and I am sorry for those who think they have!

 

[Risteard]

Based upon the answers given by you and others in this thread staying with TT looks to be the easier and potentially better option.

Interesting to learn the difference between PME and TN-C-S, I thought the terms were interchangeable.

For anyone else that finds this thread in future and would like a school day according to Google:-

Wrong way round. PME is one type of TN-C-S system.

 

[ericmark]

Possibly.
The other explanation could be that the GPO attached a wire to the water pipe to use as an earth for the telephone line. Back in the day, it was used for a shared service or for lightning protection.

I thought it was down to the party line, it was how each party selected the phone?

 

[ericmark]

Thanks for the explanation. Looks like the dangers are small but you can be unfortunate. Then again I wonder how many earth rods have rotted away to nothing or been disconnected completely over the years.

Had it with late parent's house, I could find no sign of there ever being an earth other than for GPO party line. I know there was one, as when a boy, I had blown a 13 amp fuse with a line to earth error. But could not find any sign of what it had been. So I phoned the DNO and asked what earth the house should have, they didn't know, so sent an inspector, and he gave us a TN-C-S earth free of charge.

A bit late for you to do that, as it seems they already know you are on a TT supply, which to be frank would not worry me, if anything it is a better system.

This house is both TN-S and TN-C-S depending on if running from batteries, or from DNO. This is why I have an earth rod, it is so it has an earth should the DNO power fail. Since the inverter links neutral to earth if there is a power cut, it is a TN-S not a TT supply.

But I would not be worried about a TT supply, in some ways safer than a TN-C-S supply.

 

[securespark]

I thought it was down to the party line, it was how each party selected the phone?

Yes, as I said...

Possibly.
The other explanation could be that the GPO attached a wire to the water pipe to use as an earth for the telephone line. Back in the day, it was used for a shared service

But also

...for lightning protection.

 

[Ragnar_AT]

TN-C-S only means the PEN is earthed and at some point split into a neutral and CPC. In theory, the PEN could be earthed only once, at the transformer.

The huge advantage of TN over TT is the extremely low fault impedance and the advantage of TN-C (-S) over TN-S is cost savings. Only having to run three-core and using the armour as the PEN saves the DNOs loads of money. I don’t think TN-S has ever been used in Europe outside the UK, except local supplies (factories with their own medium voltage transformers and very short low voltage distribution).

Loss of PEN was a substantial risk in TN-C installations with PEN conductors as small as 1.5 copper or 2.5 aluminium and lots of dodgy junction boxes, much less so in DNO distribution. Some DNOs also didn‘t allow TN on overhead supplies, especially those with individual bare conductors.

 

[StuB]

Wrong way round. PME is one type of TN-C-S system.

Thanks for the correction and goes to show you have to be careful what you read.

 

[bernardgreen]

Loss of the PEN in the local network appears to be a power cut. A problem but not a safety hazzard.

WRONG all the items that are earthed by CPC will now have a CPC "earth" that will be close to 240 Volt above Ground

A person holding an item with a CPC earth ( 240 Volt above ground ) will be "safe" until they also touch the ground/

A electric car being earthed via the house CPC will become Live if the PEN is lost. Live car bodywork and wet ground around the car created a very high risk of shock

That is why TT should be used as the only earth for a car being charged

 

[ebee]

That is why TT should be used as the only earth for a car being charged

Providing that you are well clear of any TN Earth via sufficient distance or robust barrirers (Insulation) in all circumstances.

 

[SUNRAY]

Loss of the PEN in the local network appears to be a power cut. A problem but not a safety hazzard.

WRONG all the items that are earthed by CPC will now have a CPC "earth" that will be close to 240 Volt above Ground

A person holding an item with a CPC earth ( 240 Volt above ground ) will be "safe" until they also touch the ground/

Indeed... https://www.diynot.com/diy/threads/a-real-moan-tonight.552183/

A electric car being earthed via the house CPC will become Live if the PEN is lost. Live car bodywork and wet ground around the car created a very high risk of shock

That is why TT should be used as the only earth for a car being charged

 

[ericmark]

That is why TT should be used as the only earth for a car being charged

I agree, all other similar items, caravans, boats, portacabins, etc, are not permitted TN-C-S it has to be either TN-S or TT. The clarification that caravan like structures such as mobile homes must not use a TN-C-S supply I can see will cause problems, I hate the clarification, a change in the regulations' means only new stuff is covered, clarification means old stuff is regarded as non-compliant even if at the time we thought it did comply.

Why cars are different to a motor caravan, I fail to understand. Why is TN-C-S permitted with a car, but not a motor caravan?

 

[StuB]

I asked Octopus to clarify what they will accept for the gas bonding and they came back with the following.

"Where gas or water services are constructed of plastic, and the customer’s pipework does not introduce an extraneous-conductive-part (i.e. does not enter the ground or other conductive parts), main protective bonding is not required in accordance with Regulation 411.3.1.2.

Where main protective bonding is required, bonding conductors shall be connected directly to the Main Earthing Terminal (MET) in accordance with Regulations 411.3.1.2 and 544.1.1. Bonding conductors shall not be looped between services unless installed as a single continuous conductor."

Looking at the photos of our supply pipe they look to be yellow plastic so hopefully that covers it anyway however as the surveyor reported the earthing to be good on the gas when the earths were disconnected from the consumer unit I went looking for any bonding.

Using a snake camera I've just found that it is already bonded behind a cupboard where the supply enters the house using the cable that then runs on to the water stopcock.



It looks to me like the cable(s) is crimped to a ring connector and I'm not sure whether it is two cables that have been crimped together or one that has folded back on itself.

From the discussions earlier in this thread my understanding is that both should be acceptable as a single continuous conductor but I hope they see it that way too.

The cupboard is low down and has big drawers in it so I think I'll put a hole cutter through the back of the cupboard to make the joint accessible and to be able to get a better photo. I'll take care not to damage either the cables or the gas pipe mind.

 

[Ragnar_AT]

Loss of PEN in three-phase distribution also means floating neutral, i.e. multiple single-phase installations are effectively connected in series between two phases, which can cause line voltage to go close to 400 V. I‘ve seen that happen in a building with a three-phase TT supply, the neutral connection to the DB was lost, frying several small items like phone chargers and radios.