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.

 

[Risteard]

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?

The conduit will still need to be Earthed. If the conduit's in bad enough condition it may not be usable.

 

[Ratmeister]

The conduit will still need to be Earthed. If the conduit's in bad enough condition it may not be usable.

Imagine a warehouse with 2 offices at one side. These have high quality conduit that the sockets and lights use as earth. The CU is at the other side of the warehouse approx 10 metres away. Could you not just run an earth cable from the CU inside plastic conduit and connect it to the metal conduit?

 

[davesparks]

. Could you not just run an earth cable from the CU inside plastic conduit and connect it to the metal conduit?

That depends on why. What is wrong/has happened to the original conduit to make this necessary?

This really needs to be looked at by a good electrician, we've got nothing more than a picture of a light switch to go on here

 

[Ratmeister]

That depends on why. What is wrong/has happened to the original conduit to make this necessary?

This really needs to be looked at by a good electrician, we've got nothing more than a picture of a light switch to go on here

Thanks Dave. I'm just being hypothetical here to see if I understand how it's supposed to work. I'll speak to the electrician again to see precisely why he thinks the earth in the metal conduit isn't acceptable.

At least I know now from your help that the wiring regulations permit it.

 

[Ratmeister]

The electrician says there is a section of older conduit coming across the warehouse that is rusted slightly and is probably reducing the earth readings. The conduit in the actual offices themselves is in good condition. I suggested we try to connect a new earth cable to the conduit inside the offices if possible but he says he can't do that as changing the CU to a new box is in effect a new installation now and using conduit for earth is an old way of doing things.

I'm really confused now.

 

[James]

Nothing wrong with using conduit as an earthing system.

 

[pc1966]

I suggested we try to connect a new earth cable to the conduit inside the offices if possible but he says he can't do that as changing the CU to a new box is in effect a new installation now and using conduit for earth is an old way of doing things.

It might be the "old way" in some installations, but for many where high strength and robustness is needed (industrial, agriculture) it is still the preferred option. A quick check on any electrical wholesale place will show plenty of conduit and related accessories for sale today!

I'm really confused now.

I think your electrician is confused, or at least not very experienced.

Conduit is capable of perfectly good use and earth continuity but, as mentioned above, the ends have to be reliably connected to the fuse box / distribution board and the can be done in many ways.

Worse case is an idiot cuts the conduit off instead of adapting the box or using some trunking to link metal parts, etc.

 

[davesparks]

The electrician says there is a section of older conduit coming across the warehouse that is rusted slightly and is probably reducing the earth readings.

what are those earth readings? have they actually tested anything?
and if they are being reduced then that is a good thing as the readings should be as low as possible. poor connections would increase the readings!

"rusted slightly" sounds to me like a bit of paint is required, not a rewire, but again I haven't actually seen it to know for sure.
if it is very rusty then the conduit may need to be replaced regardless of how the earthing is done as it would no longer be providing adequate protection to the cables.

The conduit in the actual offices themselves is in good condition. I suggested we try to connect a new earth cable to the conduit inside the offices if possible but he says he can't do that as changing the CU to a new box is in effect a new installation now

no, it doesn't become a new installation, changing a CU is an alteration to an existing installation.

and using conduit for earth is an old way of doing things.

so what if it is an old way of doing things? just because it is old it doesn't mean it cant be done now nor kept in service. Granted most of us wouldn't use steel conduit as the earth for circuits these days for new work but that doesn't mean you can't maintain an existing installation.
I look after a few installations where old conduit and trunking has been installed in this way and normally the only issues i have with earthing is fixing what some cowboys have done to modify the installations over the years

I'm really confused now.

I think your electrician is confused.

 

[Ratmeister]

what are those earth readings? have they actually tested anything?
and if they are being reduced then that is a good thing as the readings should be as low as possible. poor connections would increase the readings!

"rusted slightly" sounds to me like a bit of paint is required, not a rewire, but again I haven't actually seen it to know for sure.
if it is very rusty then the conduit may need to be replaced regardless of how the earthing is done as it would no longer be providing adequate protection to the cables.


no, it doesn't become a new installation, changing a CU is an alteration to an existing installation.

so what if it is an old way of doing things? just because it is old it doesn't mean it cant be done now nor kept in service. Granted most of us wouldn't use steel conduit as the earth for circuits these days for new work but that doesn't mean you can't maintain an existing installation.
I look after a few installations where old conduit and trunking has been installed in this way and normally the only issues i have with earthing is fixing what some cowboys have done to modify the installations over the years


I think your electrician is confused.

Thanks Dave, if you were my electrician my life would be a lot easier. I've asked them to fully test the circuits today. If the readings are too high and he insists on a rewire then I'll get someone else in for a second look.

 

[littlespark]

Get your electrical to quote for a rewire, and post it up here…. We could do with a laugh.

 

[davesparks]

If it's a point for point rewire then it should be relatively cheap as its just pulling new cable in to existing conduit.

 

[rewireIT]

Get a spark in that knows what he's doing. Suggest he read the regs book that he's supposed to keep in his van.

 

[Ratmeister]

If it's a point for point rewire then it should be relatively cheap as its just pulling new cable in to existing conduit.

There's so many sockets and circuits though, it would cost a fortune in labour I assume. There's 8 offices within the warehouse in total that are all done the same way.

 

[Ratmeister]

Get a spark in that knows what he's doing. Suggest he read the regs book that he's supposed to keep in his van.

He told me straight out that metal conduit used as earth is not allowed in new installs.
He also told me that changing the CU meant the entire install had to be treated as a new install.
I'm trying to work with it for now and I hope he'll have a read of the regs before he returns after my subtle prompting.

 

[littlespark]

The regs ask for a cpc on every circuit... whether that be a separate earth wire, steel conduit, or the steel strands around a heavy duty armoured cable. Steel conduit, properly installed, is the most substantial of any of these.

 

[James]

I have had similar discussions with clients and other electrical contractors working the same site.
sometimes it comes to a meeting with a client and contractor and myself.

I normally stay fairly quiet, just put my point across at times.
Eventually it will come down to the other guy telling me in front of the customer that I am wrong and it has to be done "this way" because it is "against the regs" to do what i suggest and that i should go away because i don't understand.

it always makes for an interesting few minutes when I place a copy of the regs book on the table and ask them to point it out.

I have found over the years that a lot of people confuse the way they were taught it should be done with an imaginary regulation specifying that it must be done that way.

p.s. To this day, I have never walked out of a meeting like that feeling embarrassed that i had got it wrong, you can normally tell you are on a winner when your opponent keeps telling you its against the regs but will never tell you which one.

 

[rewireIT]

Exactly as James says - just ask him to point out what regs it contravenes and where it specifies a DB change means existing wiring, accessories and containment has to be treated as new. He won't be able to show you them because they don't exist.

 

[davesparks]

He told me straight out that metal conduit used as earth is not allowed in new installs.
He also told me that changing the CU meant the entire install had to be treated as a new install.
I'm trying to work with it for now and I hope he'll have a read of the regs before he returns after my subtle prompting.

Someone like that is unlikely to change their mind based on a customers research from the Internet or advice from a forum.

The second point is an unfortunately common misconception which is quite prevalent in domestic work but usually less so in commercial.

It should be pretty obvious that replacing a distribution board on an existing installation does not magically change anything about the existing installation or somehow turn it into a new one.
Yes whoever does the job will need to ensure that the installation is in a safe condition for continued use, but they don't have to do everything that would be necessary to make it fully compliant as if it was installed today.

 

[Risteard]

Thanks Dave, if you were my electrician my life would be a lot easier. I've asked them to fully test the circuits today. If the readings are too high and he insists on a rewire then I'll get someone else in for a second look.

In fairness very few electrical contractors would have test equipment to perform high current continuity tests on containment now.

 

[davesparks]

In fairness very few electrical contractors would have test equipment to perform high current continuity tests on containment now.

Yes but it can be hired for a relatively small cost.