Conversion to PME

[dmcclymont]

I have seen a lot of mention re : conversion from TT styled earthing to alternative by the DNO, I was considering asking for this where I live (old overhead cables) - but...

1. Do reasons exist why it could not be done e.g. the overhead is very very old?
2. Are there costs involved?
3. Is it really worth the grief - I have a modern split load box so the whole house is on a RCD? would it really add more safety?

Interested to hear comments, and I think it would answer a lot of future questions as well?

 

[andy]

it can only be changed to PME is the neutral is reliable. worst case is neutral can go down, but phase still work.

its probably only worth changing if your re-wiring the house or changing the CU

 

[dmcclymont]

Lol, I do not think any of the wires are realiable knowing the state of the local network will prob give them grey hair asking for anything to be done!

I am not really worried about our house because it is recently checked etc but I suspect a few hundred of the houses in the village prob have wire fuses and either a voltage leak breaker or nothing in it!

Are there costs involved with it at all - perhaps it would be cheaper for people to request PME rather than pay for fitted RCDs etc?

 

[plugwash]

PME conversions can only be done if the supply is up to PME standards. This iirc means the drop from the rec pole to your house has to be concentric and the neutral has to be tied to earth at the pole.

personally i can't say i'm a fan of either PME or TT. with TT you are totally reliant on a RCD that is unlikely to get tested very often. with PME danger can be caused by a lost neutral in the supply system.

costs of PME conversion seem to range from free up to about £100 so it can be more economical than buying a 100ma time delay rcd incomer.

 

[Spark123]

Another cost to consider, the earthing arrangements may also need uprated if converting TT to PME.

 

[Lectrician]

Earthing arrangements?? AKA Bonding?? The same for TT or PME - but the DNO will require you to upgrade before they PME.



PME regs seem a little slack recently - I have seen PME on several service drops which are two core to the house wall, and then concentric to the head.

Not every pole has to have the neutral earthed down, every other 4 rings a bell.....

I would be interested if anyone has the rules.....?

I may get chatting to my DNO mate at some point......

 

[andy]

Earthing arrangements?? AKA Bonding?? The same for TT or PME - but the DNO will require you to upgrade before they PME.

you can use 6mm for TT. must be at least 10 for TNCS/TNS