Safe zones and Earth cables

[bookworm1632]

Actually what is that??

What is what? The second photo?
You see the top/back of the electric meter cupboard with the tails and earth cables emerging - they disappear into the wall cavity and work their way around to the Consumer Unit.

 

[littlespark]

There's a 150mm safe zone down the internal corner anyway.

If the existing cable goes into a cavity... can you tie on the new cable and pull it up through the same route?

 

[default]

"As it is clipped direct and it is apparent where it is running to I do not think you need to worry about it. The whole idea is avoiding hidden cable being damaged. This is not hidden just goes straight through the wall to the other side where it can be seen so very little chance of someone deciding to drill exactly where the cable goes through. That is if I am understanding you correctly in your description."

See this makes no sense to me.
How could there be a risk in drilling into an earth cable, that was magically NOT there when drilling into an earthed conduit?

The two are at exactly the same potential at all times.

If you want to install it internally then on the surface. Clipped or in containment.

 

[default]

What is what? The second photo?
You see the top/back of the electric meter cupboard with the tails and earth cables emerging - they disappear into the wall cavity and work their way around to the Consumer Unit.

Ok. What's the white T&E. You'll have to fire seal all that as well.

 

[bookworm1632]

I had thought about this - if possible it's the ideal solution, but the cable doesn't feel that loose and there's at least one pinch point where it runs through the side of the plywood frame the plastic electric box is mounted in, before it enters the cavity.

It's certainly worth a try, but I don't have high hopes of success.

 

[bookworm1632]

Ok. What's the white T&E. You'll have to fire seal all that as well.

The white T&E isn't connected to anything - think it dates back to when the property had storage heaters.
I'll remove it when I sort the earth out.

 

[Rockingit]

Few things to unpack, here.

1) The difference between an earth cable and earthed conduit is that the conduit doesn’t need mechanical protection - it IS the mechanical protection. Hence it’s very difficult to accidentally damage and thus doesn’t need to be in a safe zone.

2) The regs allow a 150mm margin in the creases of walls and the ceiling for just this purpose.

3) Yes, an earth cable (regardless of Earthing or Bonding usage) still needs to be run in a safe zone because it is still considered a conductor (and under fault conditions becomes exactly that). It is for this reason that we refer to the earth wire in final circuits etc as the CPC - Circuit Protective CONDUCTOR.

Make sense?

 

[bookworm1632]

Few things to unpack, here.

1) The difference between an earth cable and earthed conduit is that the conduit doesn’t need mechanical protection - it IS the mechanical protection. Hence it’s very difficult to accidentally damage and thus doesn’t need to be in a safe zone.

2) The regs allow a 150mm margin in the creases of walls and the ceiling for just this purpose.

3) Yes, an earth cable (regardless of Earthing or Bonding usage) still needs to be run in a safe zone because it is still considered a conductor (and under fault conditions becomes exactly that). It is for this reason that we refer to the earth wire in final circuits etc as the CPC - Circuit Protective CONDUCTOR.

Make sense?

1) It's just as easy to drill into a conduit as an earth cable - if anything it's more likely that you'd damage a conduit as it won't move, while a cable inside a conduit can move around.

2) Not sure why you're quoting this at me - it's irrelevant here.

3) I disagree - I believe it's an oversight because under fault conditions AN EARTHED CONDUIT equally becomes a conductor. Ergo if you allow an earthed conduit in a region, there is no reason to disallow an earth cable in the same area.

More evidence that the regs here do not consider sole earth cables is the requirement for RCD protection for buried cables - this is called belt and braces because it means that you're not solely relying on the person knowing where the safe zones are and thus where not to nail and as a final precaution, the reason for the earthed conduits is so that in the event the RCD fails, you still provide a lower resistance path for the electricity to take in the event someone nails through the cable. It's all clearly designed around power cables.

Of course the fact it may be an oversight doesn't mean the rule can be ignored and most people would err on the side of caution and assume SOME of the same rules apply to earth cables too - clearly not all of them as it would be pretty stupid to run an earth cable inside an earthed conduit and you certainly can't hook up an RCD, but until the IET clarifies the matter it would seem most electricians would consider safe zones apply.

 

[DPG]

The trouble is if you drill through a hidden earth cable you might not realise. If you drill through a SWA you will trip the OCPD.

 

[bookworm1632]

The trouble is if you drill through a hidden earth cable you might not realise. If you drill through a SWA you will trip the OCPD.

Agreed, but that's true no matter where it's located.

It's also quite unlikely that you'd break the cable just damage the insulation.

I kind of think you're looking for a rationale as to why the rule is there for earth cables, rather than looking at the bigger picture and realising they haven't been considered, although it's quite possible that if they were considered, the fundamental rules could be the same for the reason you state - but I think it likely that the wording of the regs would be more relevant.

 

[nicebutdim]

1) It's just as easy to drill into a conduit as an earth cable - if anything it's more likely that you'd damage a conduit as it won't move, while a cable inside a conduit can move around.

Masonry bits will drill through steel conduit, but not quickly or easily and certainly not in a manner that would escape the attention of whoever is using that drill.

 

[davesparks]

See this makes no sense to me.
How could there be a risk in drilling into an earth cable, that was magically NOT there when drilling into an earthed conduit?

There is no magic involved, the risks are different.

Live cables are run in safe zones or otherwise protected to reduce the risk of electric shock when they are damaged.

Protective conductors are run in safe zones or otherwise protected to reduce the risk of them being damaged.

There is a risk that a protective conductor could be drilled through or otherwise damaged and nobody would be aware of it, this could leave an installation in a potentially dangerous condition which may not come to light until it is too late.

 

[DPG]

Agreed, but that's true no matter where it's located.

It's also quite unlikely that you'd break the cable just damage the insulation.

I kind of think you're looking for a rationale as to why the rule is there for earth cables, rather than looking at the bigger picture and realising they haven't been considered, although it's quite possible that if they were considered, the fundamental rules could be the same for the reason you state - but I think it likely that the wording of the regs would be more relevant.

No, you could quite easily hit the copper and reduce its CSA. And you would never know.

 

[bookworm1632]

No, you could quite easily hit the copper and reduce its CSA. And you would never know.

As I stated, that is true no matter where the wire is located.

You're fishing lol.

 

[DPG]

As I stated, that is true no matter where the wire is located.

You're fishing lol.

I was replying to your comment where you said you'd probably only damage the insulation. Not sure why the fishing comment?