Earthing a metal container

[Feel the power]

OK thanks I will put the CPC of the t+e in a crimp and make sure it is taped and clear of touching anything and just connect up the TT system and keep it out the way of the TN-C-S then that should be fine then as only the container will be on the TT system

 

[EFLImpudence]

This is the best advice so far:

2. Don't do the job

 

[flameport]

In that situation, if the measured resistance to ground of the container were low enough, would it be acceptable to regard it as the 'earth electrode' and therefore not bother with a rod?

If low enough then you could.

Given the circumstances, making it TT is almost certainly not the best option anyway.

 

[Feel the power]

Flameport what would you recommend?

 

[JohnW2]

In that situation, if the measured resistance to ground of the container were low enough, would it be acceptable to regard it as the 'earth electrode' and therefore not bother with a rod?

If low enough then you could.

As I went on to imply, I don't think I would necessarily be comfortable with that. Even if 'low enough' when measured, the resistance could become quite high if/when the container found itself sitting on bone dry ground. A rod at least goes a significant distance below the surface.

Given the circumstances, making it TT is almost certainly not the best option anyway.

That may be true, but opinions will undoubtedly vary. If replacing the T+E feed is 'not possible', then, pragmatically, I think one would either have to TT the container or else hang an additional meaty earth/bonding conductor from the catenary wire - I can't think of any other options.

Kind Regards, John

 

[bernardgreen]

If you were TTing the container, you would not connect the CPE of the T+E feed to anything in the container (and you would make sure that it could not be touched). Only the local TT rod, main bonding to the container and the connection to the local CU would be connected to the container's MET.

I totally agree with John

The container MUST be supplied as TT and its CPC MUST be connected to an effective ground rod to ensure that anyone standing on the ground and touching the exterior of the container will be at the same potential as the container's exterior metal work.

 

[securespark]

The cpc of the T&E must be connected to the electrode?

 

[bernardgreen]

The container MUST be supplied as TT and its CPC MUST be connected to an effective ground rod

The cpc of the T&E must be connected to the electrode?

No it must not be connected to the electrode ( ground rod ) that is connecte to the container and it's CPC

The CPC in the Twin and earth cable is the CPC from the house's wiring. It is NOT the CPC of the container's wiring.

 

[Lectrician]

Most containers are clear of the ground, on four legs, the legs on blocks or pavers, or quite often wooden sleepers.

It needs to be TT, with a rod.

 

[JohnW2]

The cpc of the T&E must be connected to the electrode?

No - as I said to the OP, the CPC of the T+E feed must NOT be connected to anything! On the contrary, care has to be taken to ensure that it does not come in contact with any of the earthing/bonding system of the container.

Kind Regards, John

 

[RF Lighting]

I would TT the supply at the container but this presents an issue with the non-RCD protected feed entering the metal container / metal consumer unit, so the supply would need an upfront 500mA type S RCD at the supply end.

 

[JohnW2]

I would TT the supply at the container but this presents an issue with the non-RCD protected feed entering the metal container / metal consumer unit, so the supply would need an upfront 500mA type S RCD at the supply end.

I'm trying to get my head around that suggestion, so perhaps you can help me. If the metal container and consumer unit are earthed/bonded to the local TT, and the T+E's CPC is isolated from the container and everything in it, is there really a need for that RCD? The feed cable itself will be protected by whatever OPD is at its origin - just as would be the case if we were talking about a trailing cable feeding a Class I portable appliance in the garden.

Is the OP's set up materially different from 'how it should be', with SWA (from a TN-C-S installation) feeding a TT'd outhouse. If, as would be adequate, one used 2-core SWA, with the armour earthed at the house end but isolated from everything in the outhouse, we would probably be advising that there should be no RCD protection of that SWA (RCD protection being provided in the outhouse).

What am I missing?

Kind Regards, John

 

[RF Lighting]

If the feed from the house some how comes into contact with the container or the CU housing the resistance of the earth rod will be too great to allow automatic disconnection to occur without an RCD in the supply.

 

[JohnW2]

If the feed from the house some how comes into contact with the container or the CU housing the resistance of the earth rod will be too great to allow automatic disconnection to occur without an RCD in the supply.

Fair enough - so the problem is really the metal CU (wretched regs ), and you would be saying the same even if the supply were SWA?

Kind Regards, John

 

[securespark]

The container MUST be supplied as TT and its CPC MUST be connected to an effective ground rod

The cpc of the T&E must be connected to the electrode?

No it must not be connected to the electrode ( ground rod ) that is connecte to the container and it's CPC

The CPC in the Twin and earth cable is the CPC from the house's wiring. It is NOT the CPC of the container's wiring.

Is it just me who thinks what you wrote was utterly ambiguous?

"its CPC MUST be connected to an effective ground rod" sure as heck sounds like you are saying to connect the cpc of the incoming supply cable to the electrode. Obviously you are not, but it is far from clear.

If you meant the cpc's of the circuits within the container, you surely would have written "its CPC's...." but even that is ambiguous as it is not entirely clear what "it" refers to.

1 letter makes all the difference.