Circuits earthed on metal box/conduit: Does it need a rewire?

[Ratmeister]

I'm getting an old fuse board upgraded in an office block. The electrician has just told me that most of the circuits don't have earth cables coming directly from the fuse box.

I've taken a photo of one of the light switches. (attached to post)

1. It has the earth attached to the metal switch box.
2. All the sockets are done the same way.
3. All the conduit for these circuits are metal.

I need an NICEIC certificate for these offices. He has said we will need to rewire everything and there is no way around this.
I am seriously stressed now as this will cost a fortune.
Is this totally correct? If not, does anyone have any other ideas how to get this certified without rewiring?

 

[SJD]

If the wiring is in metal conduit, then that would (or should) be the earth! Perhaps your "electrican" has not met this type of wiring before, in which case he shouldn't be doing the work!

NB: I once saw a flat needlessly rewired with twin & earth pulled into every metal conduit that was perfectly OK for continued service!

 

[davesparks]

Suggest to your electrician that they should check regulation number 543.2.1 in the current wiring regulations, this permits metal conduit to be used as a protective conductor (earth)

The installation will need to be thoroughly tested to ensure that the conduit is still in suitable condition to be the earth for the circuits.

 

[Ratmeister]

If the wiring is in metal conduit, then that would (or should) be the earth! Perhaps your "electrican" has not met this type of wiring before, in which case he shouldn't be doing the work!

NB: I once saw a flat needlessly rewired with twin & earth pulled into every metal conduit that was perfectly OK for continued service!

Thanks SJD, I appreciate the response. Is this 100% okay for 18th edition wiring regulations and should not stop an NICEIC certificate being issued? I think he's saying the fuse box upgrade now means the earth cannot be on the conduit/socket.

 

[Ratmeister]

Suggest to your electrician that they should check regulation number 543.2.1 in the current wiring regulations, this permits metal conduit to be used as a protective conductor (earth)

The installation will need to be thoroughly tested to ensure that the conduit is still in suitable condition to be the earth for the circuits.

Thanks Dave, great to see it in black and white. What would the test involve to ensure it's in suitable condition? Visual inspection and the earth readings?

 

[littlespark]

whereabout in UK are you? (First part of postcode will suffice)

Maybe a forum member could give you an 'eyes on' second opinion

 

[Ratmeister]

whereabout in UK are you? (First part of postcode will suffice)

Maybe a forum member could give you an 'eyes on' second opinion

Thanks Littlespark, I have another electrician that I can get down to have a second opinion if needed. If you'd find any more photos useful for this forum post though, let me know what would be useful.

 

[littlespark]

I dont think photos will help....

Is the conduit surface or buried in the wall?
Surface, you could easily check if conduit was continuous back to board. Buried? ive seen plenty jobs where the conduit has just been cut and used as a route for running a t&e down to the switch. Either way, its easy to check continuity with the normal test equipment every sparky has.

 

[davesparks]

Thanks Dave, great to see it in black and white. What would the test involve to ensure it's in suitable condition? Visual inspection and the earth readings?

Visual inspection and a high current continuity test would be the best thing

 

[Ratmeister]

I dont think photos will help....

Is the conduit surface or buried in the wall?
Surface, you could easily check if conduit was continuous back to board. Buried? ive seen plenty jobs where the conduit has just been cut and used as a route for running a t&e down to the switch. Either way, its easy to check continuity with the normal test equipment every sparky has.

It is surface conduit over the top of brick walls. I have been on the roof (flat roof inside a larger warehouse) and it continues over the roof too between each individual office. It's in great condition. I can't confirm if the conduit connects directly to the fuse box but I'm assuming it would just be a matter of replacing the earth cable from the fuse box to the conduit if this section wasn't in great condition?

 

[littlespark]

If surface, the conduit might connect directly to the consumer unit... hopefully all from one direction.

If the conduit is buried behind the CU, it might terminate into a large square metal box with the CU in front, relying on just the fixing screws holding the CU onto the box. A big enough earth wire may need to attached to the box and brought into the new CU in addition to this.

 

[westward10]

Wouldn't that connection need to be maintenance free

 

[Ratmeister]

If surface, the conduit might connect directly to the consumer unit... hopefully all from one direction.

If the conduit is buried behind the CU, it might terminate into a large square metal box with the CU in front, relying on just the fixing screws holding the CU onto the box. A big enough earth wire may need to attached to the box and brought into the new CU in addition to this.

It's all surface conduit thoughout the building and surface conduit running to the CU. It's a different type of conduit beside the CU that is older and isn't in as good a condition though. Would the worst case scenario be that a new earth cable is needed to the better condition conduit? (Building was wired in different stages) Or is there any scenario at all where he is correct and it needs rewired?

 

[Ratmeister]

Wouldn't that connection need to be maintenance free

Hi Westward, can you explain a bit more if you have time?

 

[littlespark]

No need to rewire IF the existing cables are in good condition.

It MAY need a partial rewire, in as much as running in an earth wire through the conduit.... but it all depends on how bad the older part of conduit is.... which is why we suggested testing first.

 

[Ratmeister]

No need to rewire IF the existing cables are in good condition.

It MAY need a partial rewire, in as much as running in an earth wire through the conduit.... but it all depends on how bad the older part of conduit is.... which is why we suggested testing first.

Sorry if I'm picking this up wrong, but could we bypass the older conduit with a new earth wire that just connects the CU direct to the newer conduit?

 

[davesparks]

Or is there any scenario at all where he is correct and it needs rewired?

If the existing cable is damaged or deteriorated then it may need to be rewired for that reason.

But there is no need to rewire it for not having a seperate earth in there. The worst case scenario for that would be adding an earth wire into the conduit in any part where it is required.

 

[davesparks]

Sorry if I'm picking this up wrong, but could we bypass the older conduit with a new earth wire that just connects the CU direct to the newer conduit?

You wouldn't bypass it, you would run the earth inside the conduit.

 

[Ratmeister]

You wouldn't bypass it, you would run the earth inside the conduit.

Yep, but I mean you would be bypassing it's use as an earth? And just using the older section purely for holding the new cable?

 

[James]

Wouldn't that connection need to be maintenance free

Only if it is not accessible.
or at least that is my humble opinion.