Help needed asap regarding TN-C-S earthing

[jackarmy07]

Hopefully someone can help.

Bascially my freind bought a house and its a P.M.E system coming in to the property, But there is no direct earth connection on the cut out only a earth rod. I know this is not correct for a P.M.E system but will it suffice or do you suggest running a new earth from cut out to D.B and removing earth rod all together?

Many Thanks

Mark

 

[Guest123]

Depends on rod resistance, disconnection times presence of RCD's etc.

Is it definately a TN-C-S system coming in....how do you know?? is there a sticker on the cut-out??

Providing the readings and set-up are correct, I'd leave it as a TT system.

 

[jackarmy07]

RCD is fitted think its 100mA, Its 100% P.M.E coming in to the property, does he need an earth direct from cut out or is the earth rod sufficient?

 

[Guest123]

Sounds like a TT setup if there is a 100mA RCD upfront. Is there any additional 30mA RCD protection???

Providing the rod resistance is less than 200ohms I's leave it as a TT system.

 

[jackarmy07]

The 100mA is at the D.B its 100% a P.M.E system would you suggest running a seperate earth from cut out to D.B or is the earth rod o.k

 

[olly w]

I've come across this type of thing before. The DNO replace the old overhead supply with a nice new underground one, but don't bother to install a main earthing conductor from the cut out to the consumer unit.
I would carry out a Ze test on the TN-C-S supply and providing it is satisfactory install a main earthing conductor.
Removing the earth rod is then optional.

 

[telectrix]

have to disagree on removing earth rod.if there is PME and an Earth terminal is fixed to the cut-out, the rod should be disconnected. it's got to be one or the other, TNC-S or TT, not mixed. Get Supplier to install earth terminal and away you go

 

[jackarmy07]

have to disagree on removing earth rod.if there is PME and an Earth terminal is fixed to the cut-out, the rod should be disconnected. it's got to be one or the other, TNC-S or TT, not mixed. Get Supplier to install earth terminal and away you go

There is no direct earth connection at the cut out only a 10mm earth going from an earth rod to the consumer unit.will this be acceptable as an earth? I know the 2 earthily systems should not mix but is it as safe as an earth at the cut out to consumer unit?

 

[telectrix]

if you are using earth rod, TT system, then everything in the property HAS to be on RCD to achieve disconnection times and your Ze should be below 200ohms. better to utilise PME if possible