Earth Loop

[lsdweb]

I popped round to a friend's house as his RCD is tripping occasionally - it's a 15th Edition board with one RCD covering all circuits so pretty annoying.

I thought I'd start checking to make sure there was a good earth and was surprised when the Ze came out at 120 ohms - as I assumed the supply would be the same as mine (next door) ie PME / TNCS. When I opened the meter cabinet, I saw this .

The house was built by a plumber I think and maybe he took the words "earth loop" too literally!

The cable comes from the main earthing terminal, loops through the cabinet and disappears down through the cavity. I've had a hunt around and can't find an earth electrode and I doubt there's much structural steelwork in the ground for this to be connected to.

Anyway, it now has a proper connection to the PME supply with a Ze of .25 ohms.

W

 

[davie spark]

So was the house energised without a main earth as the picture would imply and you've now provided a main earth terminal?

 

[lsdweb]

The house was built in 1993 and has been this way since presumably.

 

[davie spark]

Scarey eh!

 

[alli]

I like that. Yes your honour I fitted an earth loop, I don't know how he got electrocuted............ They do say a little bit of knowledge is a dangerous thing.

 

[lsdweb]

the plumbing looks ok thougha!

 

[Guest123]

Looks like the house is still on the 'temp supply' from when it was being built.

Chances are, there is an earth rod buried away somewhere as the DNO wouldn't power up the head on a new build or let you use their earthing system until the house was finished and certified. To have power on site to work with, you had to provide your own temporary earthing system and when the house was finished you contact DNO and they come out and give you the permanent supply and connection to their earthing system.

Looks like a phonecall is needed.

 

[GLENNSPARK]

Looks like the house is still on the 'temp supply' from when it was being built.

Chances are, there is an earth rod buried away somewhere as the DNO wouldn't power up the head on a new build or let you use their earthing system until the house was finished and certified. To have power on site to work with, you had to provide your own temporary earthing system and when the house was finished you contact DNO and they come out and give you the permanent supply and connection to their earthing system.

Looks like a phonecall is needed.

Yes and a schedule of tests Ze Zs etc as the supply characteristics have been altered here now

 

[lsdweb]

Thanks guys - the full range of tests was on the cards anyway to try and resolve the RCD issue.

W