Earthing of a conduit

Jon Lester · Aug 18, 2021

Hi there I work in a shopping centre and the tills are supplied by a chrome pole ( non standard ) that comes from a metal burgess ceiling . Inside the pole is a 2.5mm 3 core flex and a CAT6 cable (non screened ) that supplies the till . This pole does not have any earth . I’m now being asked to use an earth clamp to connect the pole to a piece of trunking above the ceiling via a 4mm cable . Question 1 is this necessary? Question 2 should the earth from clamp be connected to the same earth that is contained in this pole ? And question 3 should the CAT6 cable be installed in same containment as the power supply ?

timhoward · Aug 18, 2021

I would say (without reference to regs book)
Q1 - The metal pole should be bonded somehow - consider it as metal conduit / trunking
Q2 - more of a concern is that I would like to see the bonding connected to a bonding conductor ideally, not another item that is bonded.
Q3 - no, Band I and II cables shouldn't be contained together

Jon Lester · Aug 18, 2021

timhoward said:
I would say (without reference to regs book)
Q1 - The metal pole should be bonded somehow - consider it as metal conduit / trunking
Q2 - more of a concern is that I would like to see the bonding connected to a bonding conductor ideally, not another item that is bonded.
Q3 - no, Band I and II cables shouldn't be contained together

Thank you Tim these are what has been done already . I’m sure that this is wrong . Any regs references would be very helpful if possible too .

[ElectriciansForums.net] Earthing of a conduit

timhoward · Aug 18, 2021

In no particular order, as I find them...
528.1 ....neither a voltage Band 1 nor a voltage Band II circuit shall be contained in the same wiring system....
(covering Q3, there is no question here, definite no no for data / alarm cables to be in same containment as supply cables)

411.4.2 ...exposed conductive parts of the installations shall be connected by a protective conductor to the main earthing terminal.
(It's clear the poles need earthing. 543.2 would allow the trunking to be used as a protective conductor assuming it is itself earthed. 544.2 confirms 4 sq mm is ok. So from what I can tell the method you have been using is probably ok)

Mikegh · Aug 18, 2021

Agree with above

Sounds like a DIY job on the pipe drop, those systems are probably expensive for the proper gear

Data and Mains cables in the same pipe and no connection tag

Mikegh · Aug 18, 2021

Supermarket electrical installations are well known for cutting corners

Probably the nature of the business, very competitive overall

Jon Lester · Aug 18, 2021

timhoward said:
In no particular order, as I find them...
528.1 ....neither a voltage Band 1 nor a voltage Band II circuit shall be contained in the same wiring system....
(covering Q3, there is no question here, definite no no for data / alarm cables to be in same containment as supply cables)

411.4.2 ...exposed conductive parts of the installations shall be connected by a protective conductor to the main earthing terminal.
(It's clear the poles need earthing. 543.2 would allow the trunking to be used as a protective conductor assuming it is itself earthed. 544.2 confirms 4 sq mm is ok. So from what I can tell the method you have been using is probably ok)

Thanks Tim that really helps a lot . The only issue I thought with the trunking was that if the earth to the trunking was to be disconnected for whatever reason then it would lose its earth to the pole too .

James · Aug 18, 2021

If the cables are double insulated, are you sure the pipe requires bonding?
also, there are types of data cable that can be run in the same trunking as power.

GBDamo · Aug 18, 2021

[Devil's Advocate]
If the cable is 6491singles, insulation and no sheath, then the down pipe is acting as part of the electrical installation, is exposed, conductive and should be earthed.

However if the cable is 6492 or flex, insulated and sheathed, then the down pipe is simply cosmetic, not forming part of the electrical installation, just making the cable drop look pretty.

I'd argue it is not protecting the cable from likely mechanical damage (such as in a traffic area) in which case it is part of the electrical installation and would need earthing.

I know we all hate them but consider the "double insulated" class 2 metal light fittings that are not earthed yet are metal thus conductive but because the wires within are insulated and sheathed they are permitted, as are other similar class 2 metal bodied appliances.
[\Devil's Advocate]

The above assumes these poles aren't extraneous.

The data is a different matter, that's a definite no no, although ubiquitous.

timhoward · Aug 18, 2021

GBDamo said:
If the cable is 6491singles, insulation and no sheath, then the down pipe is acting as part of the electrical installation, is exposed, conductive and should be earthed.

However if the cable is 6492 or flex, insulated and sheathed, then the down pipe is simply cosmetic, not forming part of the electrical installation, just making the cable drop look pretty.

I'm going to reflect on that while conceding you may be right! The definition of electrical installation is so broad in section 2...

Hypothetically if you had a run of steel trunking within a single room that only had T+E in it, would you not earth it then?

My thinking was whatever the cable is, extreme things like this can still happen (fresh in mind from video I posted earlier today) and earthing the pipes feels like a good plan.

Jon Lester · Aug 18, 2021

James said:
If the cables are double insulated, are you sure the pipe requires bonding?
also, there are types of data cable that can be run in the same trunking as power.

The flex is double insulated but could possibly be damaged going into the pole , and the cables are not screened cables so I think it’s not correct

GBDamo · Aug 18, 2021

[/QUOTE]

Jon Lester said:
The flex is double insulated but could possibly be damaged going into the pole , and the cables are not screened cables so I think it’s not correct

That is an issue of good workpersonship.(?)

Even if we agree its a part of the electrical installation, any cables should be installed so as not to become damaged.

A coulper and brass brush on the top would solve that issue, earthing the pipe will not it merely mitigates the resultant consequences of the cable becoming damaged.

timhoward · Aug 18, 2021

I was just going to say - I think if it was contained in something that was designed to hold electrical cables, and had provision for ensuring a non-sharp exit at the top e.g. a coupler and brass bush, it would be easier to say that's fine.
There is a reg saying enclosures should not have sharp edges. So something should be done about the top exit really. Even sitting a 25mm conduit box or elbow on top would improve matters!

I also think it's hard to prove from definitions in the regs whether they are exposed conductive parts or not, you might even argue that as they poke through a ceiling they are extraneous...

One thing is for sure - the money saving method of installation has spooked someone enough to commission this work!

James · Aug 18, 2021

My biggest concern is the newly installed power and data cables above the grid have no method of support that prevents collapse in fire.

Jon Lester · Aug 18, 2021

James said:
My biggest concern is the newly installed power and data cables above the grid have no method of support that prevents collapse in fire.

I agree, there are multiple cables flying everywhere in this ceiling , no cable support whatsoever , no tray , no basket , not even cable tied up anywhere . Major fire hazard i think