Safe zones and Earth cables

[bookworm1632]

I've been told I need to upgrade the main earth bonding to 16mm.
The consumer unit is on the wall adjacent to the externally mounted incoming supply box - I basically need to run the earth wire down the corner about 1m and then across the side wall about 30cm then through and into the back of the supply box. 15cm of the horizonal run would thus be outside a safe zone.
Now I'm looking at the regs on buried cables and although they seem to be intended for power cables, I can't find any separate details on earth only cables, other than one of the exemptions listed allowing cables to be run outside of safe zones, is where the cable is either contained within earthed sheaving or earthed conduit. Given that an earth cable would be effectively no different to an earthed conduit from an electrical safety point of view given that all earth cables and earthed fixtures are always at the same potential (or should be) within a property. But that's logical and doesn't necessarily mean it's right.
The other factor is the requirement for buried cables to be protected by RCD's - clearly not something that can apply to an earth only cable, which makes me think that safe zones don't really apply here.....

Thoughts?

 

[Vortigern]

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.

 

[default]

I've been told I need to upgrade the main earth bonding to 16mm.
The consumer unit is on the wall adjacent to the externally mounted incoming supply box - I basically need to run the earth wire down the corner about 1m and then across the side wall about 30cm then through and into the back of the supply box. 15cm of the horizonal run would thus be outside a safe zone.
Now I'm looking at the regs on buried cables and although they seem to be intended for power cables, I can't find any separate details on earth only cables, other than one of the exemptions listed allowing cables to be run outside of safe zones, is where the cable is either contained within earthed sheaving or earthed conduit. Given that an earth cable would be effectively no different to an earthed conduit from an electrical safety point of view given that all earth cables and earthed fixtures are always at the same potential (or should be) within a property. But that's logical and doesn't necessarily mean it's right.
The other factor is the requirement for buried cables to be protected by RCD's - clearly not something that can apply to an earth only cable, which makes me think that safe zones don't really apply here.....

Thoughts?

Do you need to upgrade the main earth or the main bonds?? What size main fuse do you have? Do you know your earthing system? And do you know the size of the main tails or incomer??

 

[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 hidded 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 desciption.

15cm through a wall does not constitute a buried cable. How are you running the cable. Is it internal or external and is it buried in the wall or on the surface??

 

[bookworm1632]

Sorry I wasn't clear.
First photo shows the proposed route.
Second shows the windowsill removed and reveals the box the electricity meter is contained in.
I'd like to bury the cable as opposed to running it surface mounted.
If (and as I wrote above, it doesn't make any sense, but regs sometimes don't make sense) the rules regarding the location of buried cables apply here then I see I have the following options:

1) Surface mount to a position where I can drill through into the back of the electric cupboard.
2) Channel out and conceal the cable running down the corner, but surface mount the section that runs across the wall until I can drill through into the electric cupboard. If I did this, I'd run the horizontal conduit just above the skirting.
3) Drill through to exterior for some/all of cable run - cosmetically I think this is the least desirable option.
4) Find a way to run the cable as illustrated in red, that IS allowed by the regs if possible? E.g. fitting a blank faceplate?

 

[Vortigern]

Is there any reason You quoted me in your reply @default

 

[default]

Sorry I wasn't clear.
First photo shows the proposed route.
Second shows the windowsill removed and reveals the box the electricity meter is contained in.
I'd like to bury the cable as opposed to running it surface mounted.
If (and as I wrote above, it doesn't make any sense, but regs sometimes don't make sense) the rules regarding the location of buried cables apply here then I see I have the following options:

1) Surface mount to a position where I can drill through into the back of the electric cupboard.
2) Channel out and conceal the cable running down the corner, but surface mount the section that runs across the wall until I can drill through into the electric cupboard. If I did this, I'd run the horizontal conduit just above the skirting.
3) Drill through to exterior for some/all of cable run - cosmetically I think this is the least desirable option.
4) Find a way to run the cable as illustrated in red, that IS allowed by the regs if possible? E.g. fitting a blank faceplate?

 

[default]

Why does the main earth require upgrading?

 

[Vortigern]

Surely you would just go straight outside via the right side of the consumer unit?

 

[bookworm1632]

Do you need to upgrade the main earth or the main bonds?? What size main fuse do you have? Do you know your earthing system? And do you know the size of the main tails or incomer??

The main earth. The supply is currently connected to the Consumer Unit with 2x6mm earth cables which need upgrading to a single 16mm cable.

Main fuse is 100A.

Tails are 25mm I think.

 

[default]

Sorry I wasn't clear.
First photo shows the proposed route.
Second shows the windowsill removed and reveals the box the electricity meter is contained in.
I'd like to bury the cable as opposed to running it surface mounted.
If (and as I wrote above, it doesn't make any sense, but regs sometimes don't make sense) the rules regarding the location of buried cables apply here then I see I have the following options:

1) Surface mount to a position where I can drill through into the back of the electric cupboard.
2) Channel out and conceal the cable running down the corner, but surface mount the section that runs across the wall until I can drill through into the electric cupboard. If I did this, I'd run the horizontal conduit just above the skirting.
3) Drill through to exterior for some/all of cable run - cosmetically I think this is the least desirable option.
4) Find a way to run the cable as illustrated in red, that IS allowed by the regs if possible? E.g. fitting a blank faceplate?










View attachment 103978

View attachment 103979

Why do you need to upgrade the main earth?

 

[Vortigern]

Anyway that stuff whatever it is in the walls would not comply as to safe zones by the looks of it so attaching cables of any kind I would not do. That is strange!

 

[default]

The main earth. The supply is currently connected to the Consumer Unit with 2x6mm earth cables which need upgrading to a single 16mm cable.

Main fuse is 100A.

Tails are 25mm I think.

Either surface inside or as its been said drill outside and clip directly. Make sure the main tails are 25mm or they'll have to be upgraded as well.

 

[bookworm1632]

"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.

 

[default]

Anyway that stuff whatever it is in the walls would not comply as to safe zones by the looks of it so attaching cables of any kind I would not do. That is strange!

Actually what is that??

 

[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?

 

[Rockingit]

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.

I think your DIY status is all we need to know, here.