Main Earth Terminal

[sparkyspike]

so it looks like the earth spike is going to have to do....

Ah, now it's getting clearer. If you have a spike and a confirmed TT supply then you need to sort out the earth cables in the supply head. Best thing to do is to test the cables and sort out which is your main earth cable and which are bonding cables etc and whether the continuity is sufficient.

You can request a PME terminal - whether it is available or not is another thing - but it should be fairly straightforward to find out. When you call the supplier, ask for the number of the depot concerned - you can talk to an engineer directly that way.

Once you've got the PME terminal, you can connect your 16mm (if that's what you need) to the first CU and then from there you can run a cable to CU number two. If you're stuck with TT, then you can fit a MET and run everything from there.

 

[Adrian80]

This sounds a bit more than i first suspected.

I have just assumed its an earth spike, Basically there is a 16mm cable coming out the concrete next to the supply.

The bonding for gas and water go to the new CU.

the 16mm twin and earth goes back to the meter, but the internal earth isnt used and a 16mm earth is run next to it.

The old cast iron gas main and old CH use to run in next to the electric, so there is the possibility that this 16mm wire could have been used for bonding.

How can i tell if this cable is attached to an earth spike or not?

Cheers

A

 

[sparkyspike]

First thing is to find the earth spike. This could be in a flower bed, or in a pit, or anywhere really. It could even have been covered over in concrete. If you can find it, then you can measure the resistance of the cable to it and the Ze of the supply. Even if you can't find the spike, you can disconnect the cable and measure the Ze of the supply. This will at least tell you if the earth connection is sufficient, although it won't prove that it's not connected to a water pipe instead of a spike.

What sort of RCD protection do you have? Do you have a 100mA RCD at the supply? Or do you just have 30mA RCDs on the CUs? Or neither!

It's unlikely that a 16mm cable was used to bond the gas, so it probably is (or was) a main earth cable. Your supplier will be able to confirm if you already have a TN supply.

 

[Adrian80]

Just got a 30mamp on the CU, nothing on the meter side...

I think i need to the test the ze's on the earth, to check that its doing what it should be doing.

thanks sparkyspike..

should the dno be doing this, or is this my responsibility?

Adrian

 

[sparkyspike]

You are responsible for the earth connection, unless it is provided on a TN supply. As you have no 100mA RCD, it's beginning to sound like you don't have TT. Or are all of your breakers protected with 30mA RCDs?

You need to get confirmation asap as to what kind of supply you have. If you have TT, then you urgently need to address the earth connections and you will also need to ensure that the whole installation is protected with at least a 100mA RCD.

If you have a low ohm reading for Zs (e.g. 0.15 or something) then you are probably already on TN. If it is high (e.g. 150 Ohms) then you are probably on TT.

 

[Adrian80]

Hi ya,

I have a new 17th edition dual RCD unit. All the MCB's are covered by rcd protection.

But the one in there previously was out the ark... with no protection.

Should i get the DNO out or should i call a sparky?

Cheers for your advice. really appreciated.

A

 

[Spark123]

Call the electrician who fitted your new consumer unit to come and have a look.

 

[sparkyspike]

If you have a new 17th CU, then you should have a certificate with it which will show the supply type and the Ze readings. If you don't have one, then something's wrong there.

Did you have the CU fitted?

 

[sparkyspike]

You implied that the DNO are telling you that you have a TT supply and should disconnect the earth connections from the neutral block. It's looking more and more unlikely that this isn't the case. By all means call them and have them confirm what your supply is. But talk to the depot, not a customer service advisor. They shouldn't be telling you to disconnect earth cables without confirming what supply type you have.

 

[Adrian80]

Dno are sending someone out monday. Will report back then..

Cheers Again. A

 

[Adrian80]

Well then DNO came out, tested the supply by putting the meter between the live and the neutral, they ended up with a reading of 0.34, which they said was borderline but a bit high.

They went next door where the phase comes in and tested there and got a reading of 0.25

They said its a bit crap but thats it. They offered to change the cut out so there would be an earth on the outside to connect to, but he said it would be no different from firing the earth straight into the top of the neutral.

The bit of a wire which looked like a TT apparent was crap, and could just be dangling in the concrete.

He reckons there is lead and paper in the road because they changed some lights on the street a while ago. When he said that i assume he meant PME.

I am not sure if i am being fobbed off or not. He said it would cost a ton to change the cut out or 1500 quid to run PME in from the road.

The house has got a big concrete slap all the way round it, so i am not sure about banging in a spike into the concrete, also i am not sure whats under the concrete. I know the gas, water, and the drain all goes up the side of the house...

any suggestions????

 

[Adrian80]

Hi guys,
i know its been a busy day on here any pearls of wisdom? I realise you all give advice for free..
Cheers
A

 

[Spark123]

Facts of the matter are only the DNO can work on their network.
If we have to install an earth then the only type we can install is TT (with an earth spike).
If the DNO have already provided an earth then they should maintain it. The absolute max Ze for a PME (TN-CS) system is 0.35 so only just and so in tollerance.

 

[Adrian80]

The thing is the guy said it aint proper PME its plastic sheathed cable, and the ze from the neutral to live is kind of indicating that its only just good enough....

It all sounds a bit sh1t to me, and it sounds like i need to bang in an earth rod somewhere??

A

 

[Spark123]

Either it is PME supply or it isn't. It is upto the DNO to ensure that their network has Protective Multiple Earthing before allowing their neutral to be used as an earth i.e. TN-CS.