Earthing question

Peedy17 · Jul 1, 2010

Not sure this is in the right section please move if not.

I've been sent to test some temp supplies to an industrial site.
We have a large section board fed from the industrial factory side. This section board then goes around the site feeding various DBs.

The feed to this section board is in 185mm double insulated tails parrarell supply. It's 3phase 400- these tails are laid in a platic duct on the floor and protected by 60947-3 breaker.
These no earth between the industrial and our section board but the section board is a tt system.

The site wanted it to be electrically separated but I don't think it's right.

The way I see it. It should be in saw with it being glanced into an insulated glan plate at the industrial side and protected via an rcd.

What do you guys think. Sorry if it's unclear

davelerave · Jul 1, 2010

afaik if you convert to TT with a swa glanded on the supply side-it doesn't need rcd'ing on the supply side

i'm not clear on other method ?

out of interest -how is the section board configured

Peedy17 · Jul 1, 2010

davelerave said:
afaik if you convert to TT with a swa glanded on the supply side-it doesn't need rcd'ing on the supply side

i'm not clear on that method ?

out of interest -how is the secion board configured

It's not in swa mate it beautel (sp) singles. In theory if these are damaged our rcd will trip but the supply one may not as they arnt earthed

davelerave · Jul 1, 2010

"The way I see it. It should be in saw with it being glanced into an insulated glan plate at the industrial side and protected via an rcd."

i was replying to that part of your post

i'm afarid you've lost me now regarding the rcds

Peedy17 · Jul 1, 2010

Sorry. It's basically our site being fed via double insulated single core cables on a parrarell feed.

There's no earth from the eleccy board side to our supply. Our supply is protected via a tt system.

My query is that these singles arnt protected as there's no earth or armouring on them. They are laid in a duck about 10m run.
Fed via a 60947 breaker into our 61009 rcbo

I personally think they should be swa with being glanced into an insulated gland plate at the eleccy board side but earthed to out tt rod

caddy · Jul 1, 2010

"I personally think they should be swa with being glanced into an insulated gland plate at the eleccy board side but earthed to out tt rod"

you cant have the supply cables feeding the DB's from the main board but being earthed from the opposite end via your spike.

If the tails are protected by plastic ducting and the board at the feed end is earthed via a Spike then running a seperate earth with the tails isnt going to acheive anything. The only reason you would need to earth anything is if any part of the containment for the tails is metal.

Peedy17 · Jul 1, 2010

caddy said:
"I personally think they should be swa with being glanced into an insulated gland plate at the eleccy board side but earthed to out tt rod"

you cant have the supply cables feeding the DB's from the main board but being earthed from the opposite end via your spike.

If the tails are protected by plastic ducting and the board at the feed end is earthed via a Spike then running a seperate earth with the tails isnt going to acheive anything. The only reason you would need to earth anything is if any part of the containment for the tails is metal.

Thanks for that mate, wasn't sure if earthing one end and supplying from the other was ok. I thought it was.

We've got the niceic inspection next week an didn't want to get pulled on it

WayneL · Jul 1, 2010

I might be wrong, but I fail to see the difference between these 'tails' feeding your sub-board and the 'meter tails' feeding a CU in a domestic, and you don't run an earth with them.

I think your distribution tails need to be protected against mechanical damage, but as there isn't anything metal about them, I don't see what running an earth with them will achieve.

Different if they were SWA, then the armouring would need to be earthed at the supply side.

Peedy17 · Jul 1, 2010

WayneL said:
I might be wrong, but I fail to see the difference between these 'tails' feeding your sub-board and the 'meter tails' feeding a CU in a domestic, and you don't run an earth with them.

I think your distribution tails need to be protected against mechanical damage, but as there isn't anything metal about them, I don't see what running an earth with them will achieve.

Different if they were SWA, then the armouring would need to be earthed at the supply side.

The difference I tht these tails are run across a construction site floor in a duct about 10m long.
I never said I wanted to run an earth with them I said I wanted them to be swa.
If I cut one o these tails it wouldn't trip and you woul have two live ends.

I still think it should be swa bonded to our end of the supply at the tt system

caddy · Jul 1, 2010

Peedy17 said:
If I cut one o these tails it wouldn't trip and you woul have two live ends.

I still think it should be swa bonded to our end of the supply at the tt system

Well if the cables are run in a duct how would you manage to cut one ?
Either way if you really wanted to run it in an SWA you would earth at the supply end not the feed end via your spike. and make sure that there is no earth connection between the supply and your TT Spike.

Peedy17 · Jul 1, 2010

caddy said:
Well if the cables are run in a duct how would you manage to cut one ?
Either way if you really wanted to run it in an SWA you would earth at the supply end not the feed end via your spike. and make sure that there is no earth connection between the supply and your TT Spike.

It's an area of heavy traffic and it's only in ducts through the majority o it. It is free aired about 3m each end