How to earth conduit?

[mrscalex]

My reading of the regs is that since I can't run by cable within 150mm of the corners or 50 mm deep that I should contain everything within metal conduit and that this should be earthed.

So how do I make the earth connection? Is this made between socket box and conduit and conduit to conduit if joined/abutted? What type of conenction to the conduit (I was going to use top-hat capping) do I need?

Thanks.

Regards,

Robert

 

[ban-all-sheds]

My reading of the regs is that since I can't run by cable within 150mm of the corners or 50 mm deep that I should contain everything within metal conduit and that this should be earthed.

And they are also not in runs horizontally or vertically in line with wiring accessories?

So how do I make the earth connection? Is this made between socket box and conduit and conduit to conduit if joined/abutted? What type of conenction to the conduit do I need?

AIUI, the expectation is that metal conduit will be properly terminated by being screwed into conduit boxes, or bushed into ordinary ones, and therefore can be earthed via terminals in the boxes. If you'r just going to have lengths of conduit to protect cables then all I can think of two methods

1) put a thread on the end of the conduit, and use a bush to clamp a banjo to the end

2) use the straps made for earthing/bonding pipes.

Both will require you to have access to a couple of inches of exposed conduit at the end, e.g. under the floor, and I'm not sure how approved either method is.

HOWEVER:

(I was going to use top-hat capping)

Are you planning to use conduit, or top-hat capping? They are not the same thing, and the correct answer is "conduit", as capping provides no mechanical protection...

 

[securespark]

Both will require you to have access to a couple of inches of exposed conduit at the end, e.g. under the floor, and I'm not sure how approved either method is.

According to the NIC, earth straps are acceptable to bond metal "tube" (definition: metal conduit, pipe or rod)

But in the case of b/e conduit (sorry, black enamel), you must remove the paint to get a good connection with the metal surface of the conduit.

 

[shaggy]

I've interpreted this reg differently myself. Look at (iii):
Regulation 522-06-06
A cable concealed in a wall or partition at a depth of less than
50 mm from the surfaces of the wall or partition shall:
(i) incorporate an earthed metallic covering which complies with
the requirements of these Regulations for a protective
conductor of the circuit concerned, the cable complying with
BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or
BS 8436, or
(ii) be of insulated concentric construction complying with
BS 4553-1, BS 4553-2, or BS 4553-3, or
(iii) be enclosed in earthed conduit, trunking or ducting satisfying
the requirements of these Regulations for a protective
conductor, or be mechanically protected sufficient to prevent
penetration of the cable by nails, screws and the like, or
(iv) be installed in a zone within 150 mm from the top of the
wall or partition or within 150 mm of an angle formed by two
adjoining walls or partitions. Where the cable is connected to
a point, accessory or switchgear on any surface of the wall or
partition, the cable may be installed in a zone either
horizontally or vertically, to the point, accessory or switchgear.
Where the location of the accessory, point or switchgear can
be determined from the reverse side, a zone formed on one
side of a wall of 100 mm thickness or less or partition of
100 mm thickness or less extends to the reverse side.

I interpret that as you either give the cable mechanical protection which doesn't require earthing or you cover it in earthed metal which doesn't give it mechanical protection. I haven't interpreted that as you need mechanical protection which is also earthed.
For the cable from the cooker control unit to the connection box I have had the cable diagonally but I have installed metal capping and drilled a hole for a 2BA screw which I clamped an earth wire to, then took that into the box.

 

[dingbat]

Two things stick out from that quote:

The word, "enclosed" and the phrase, "satisfying the requirements of these Regulations for a protective conductor"

AFAIC capping does neither effectively.

There is, of course, a simpler solution... forget about chasing in and just clip the cable to the wall in plain view. No problems with the regs then!

 

[securespark]

a 2BA screw which I clamped an earth wire to

Hey, Shaggy, 2BA is cracking on a bit!!

 

[shaggy]

SS, I expect you would use a 4mm one but I've got a big box of BA screws and they were once the traditional thread for electrical work. 4BA is a bit small for me.
I'm still not sure about that reg though? Dingbat makes the point that capping does not enclose the cable. It doesn't on 4 sides but it encloses it on the sides that matter. I don't mind being wrong if I've interpreted it incorrectly but I don't think it's clear. Any offers?

 

[securespark]

It's the second one I am a bit worried about - to effectively earth the capping may be tricky, and to ensure that the earth connection remains sound may be awkward too.

Imagine connecting an earth conductor to a thin piece of galv steel with a screw (guess you are using nut too?), then plastering over...Conduit is indeed a huge headache, but you are guaranteed as good a level of mechanical protection as you can get, and a really sound earth connection with a clamp.

 

[ban-all-sheds]

Conduit is indeed a huge headache

A full conduit system is, but simply using lengths where otherwise you'd use capping just requires a deeper channel...

 

[shaggy]

SS:

(guess you are using nut too?)

I have fixed the screw to the capping with a nut to make an earth stud then clamped the earth wire between 2 washers and then another nut.
I’m still not clear if conduit is accepted as providing mechanical protection? If it does resist the penetration of a masonry nail then it doesn’t need earthing according to the reg. As I understand it, if the cable can be penetrated by a nail then it needs covering by earthed metal so earthed capping complies. Those metal plates that you can get for fixing over cables that lie in notched floor joists, so are not below 50mm from the top, provide mechanical protection so don’t need earthing. Surely it is one or the other; earthed metal covering or protection from penetration?

 

[lepetitgue]

Hi - I think I'm gonna go for the 150mm from a corner option...any advice
on how deep to bury the cables to avoid filler/plaster cracking. Thanx

 

[dingbat]

Surely it is one or the other; earthed metal covering or protection from penetration?

Correct, it is, under the regulations for protection of concealed cable. But it is difficult to provide good protection from penetration in all circumstances. As for steel conduit then you should earth it as a matter of course, even if you're not using it as a protective conductor, because it comprises exposed conductive parts of the wiring system.

 

[mrscalex]

I don't think it's so much how deep to do it (though I believe 1/4 in is supposed to be the minimum) but what you fill it with. I think there's something called bonding plaster to pack the chase out to just below the surface and then use finishing plaster feathered in to the surrounding area to complete.

 

[mrscalex]

Meant to say I am now going to use conduit for the horizontal runs outside of the permitted zones and not capping. My understanding of the regs is evolving all the time and I can now see that capping is nothing more than a means of containment and protection from plaster.

I was going to sit the conduit so the top is flush with the plasterboard (dot and dabbed) but exposed. The kitchen base units then go in front and you can't see any of it. I guess this almost constitutes surface cabling where presumably no protection is required but I think I'll be happier like that.

I was then going to use plastic capping (less hassle) for the vertical runs up to the sockets where the cable is in the permitted zone but obviously plaster over this where it becomes visible.

Does this all make sense?

 

[BruisedThumb]

Shaggy:

<I have fixed the screw to the capping with a nut to make an earth stud then clamped the earth wire between 2 washers and then another nut.>

Don't the regulations say that (bonding) screwed connections have to be accessible for inspection? That means you couldn't plaster over that bit of the capping.