explain this.....

[Hawk]

So on the test results (see pictures) it states TT system, earth rod, however from the picture of the supply it can be seen that there is a suppliers earth which looks like tncs to me.

 

[uksparks]

Maybe it's a bit of earth going into an earth block in the head but with no link present, looks like it's a DNO earth but maybe nothing connect? Just a thought?

 

[davesparks]

It's possible that the earth has been connected to the head at some point in time after the original installation was carried out.

Is there anything in the installation which would mean that a PME earth connection cannot be used?

Is the rod actually there?
Does the rest of the certificate make sense?

 

[Gavin A]

it clearly looks to have been TT at the time of test, given the electrode resistance results.

 

[Hawk]

I was thinking that maybe the DNO upgrade the supply after the original installation. Only thing I can think of. I suppose one way to find out is to do a ze test.

 

[Hawk]

Update.... Got called out to same job as outside lights where causing the rcd, that covers the majority of the premises, to trip. Found lose neutrals in the lighting circuit which seems to be the cause as they have been fine for 2 days now. Anyway while I was there I carried out a Ze and got a result of 0.13ohms. I would therefore say that it is tncs system.
Now that that's been determined what would your thoughts be on doing away with the rcd covering the whole board and use individual rcds? So as when a fault develops the whole board won't trip off.

 

[Lagentium]

What does the supply do, or what did it do? Most temporary site supplies are a TT installation, that can be maintained in the right circumstances.

 

[Hawk]

It's a commercial installation. Looks as if it was originally a TT system that has been upgraded to a tncs system which would make sense given the 0.13ohm Ze. This means I could use single pole rcbos as the neutral doesn't have to be disconnected if a fault develops on a tncs system. Whereas with a tt system both line and neutral have to be disconnected.

 

[TheDaddy]

it clearly looks to have been TT at the time of test, given the electrode resistance results.

My thoughts exactly!

 

[Simonslimline]

Update.... Got called out to same job as outside lights where causing the rcd, that covers the majority of the premises, to trip. Found lose neutrals in the lighting circuit which seems to be the cause as they have been fine for 2 days now. Anyway while I was there I carried out a Ze and got a result of 0.13ohms. I would therefore say that it is tncs system.
Now that that's been determined what would your thoughts be on doing away with the rcd covering the whole board and use individual rcds? So as when a fault develops the whole board won't trip off.

Were the readings the same with Ze & Zpn?

 

[malcolmsanford]

Sorry Simon have to ask....Zpn?

 

[Simonslimline]

Sorry Simon have to ask....Zpn?

Hi Malcom, i meant Z between phase & neutral.

The op seems to think that it has to be TN-C-S because the Ze is low, which may not be the case possibly.

 

[Simonslimline]

Were the readings the same with Ze & Zpn?

Sorry meant were the reading the same for PEFC & PSCC?

 

[Hawk]

Well from the picture I'm sure you would agree that it looks like a tncs system. The measurement confirmed it. Yes both the same.

 

[Hawk]

I also don't think it has to be a tncs because the reading is low. I carried out testing to confirm that it was a tncs system. Which I suspected from looking at it.