Does SWA need to be earthed-Reg required please

[Davey101]

I am testing a new installation, part of which has half a dozen plastic light fittings mounted on an outside wall. These fittings are wired with a 5/6 core SWA. One of these cores is used as the cpc. Each fitting has 2 SWA's, one in, one out.The problem, as far as I see it, is that the SWA glands have not been connected together with a banjo, meaning there is no earth continuity of the sheath. I know that this is not correct, but cannot find a specific Reg to prove my point (which I have to do). The closest I have come is REG 411.3.1.1, which states that exposed conductive parts must be connected to earth. The definition for an exposed conductive part doesnt help either, especially as it mentions 'basic insulation failing', and the inside of an SWA cable is double insulated!? I seem to remember reading somewhere that metallic sheaths must be earthed, but cannot find a specific reg. Am I missing something obvious? Time is an issue, so I would like to clear this up.

I'm after a black and white answer that I can use please,
I've also heard an argument that any unused cores should be earthed, which makes sense to me, any thoughts on this?
Many thanks, Dave.

BTW, this is my first post, so hello ;-)

 

[roukel01]

Earthing the SWA is all about providing mechanical protection to the installation. Automatic Disconnection of Supply cannot properly be achieved without earthing the steel armouring. This is so that if something such as a spade penetrates the cable, and hits the live conductor, the spade will be earthed by the armour and cause a short between live and earth, which will blow the fuse (Automatic disconnection of supply)

I havent got a regs book to hand but it states (probably somewhere in the "Erection and Selectrion" part of the big red book) about selecting appropriate mechanical protection for the surroundings.

You can class the steel armouring as an "exposed Conductive part" becasue the shroud can be removed without the use of a tool and the steel exposed, thus requiring it to be earthed.

Hope this helps!!

 

[patricklondon]

im sure theres no disputing that im not a fountain of regs knowledge but welcome to the forum dave

 

[adam.h]

is the cable not earthed at the other end?

 

[mechelec]

is the cable not earthed at the other end?

The first cable run to the first light fitting should be earthed, the problem the OP is suggesting I think is that the following fittings in series will not have armour earth continuity?

 

[robsparky1975]

check reg 543.2.5 there is no reg that says you have to bond the armourmbut you can use it as an earth if the cable does not have one,i cant say i have ever seen the armour not earthed,doesnt everyone,no specific reg that i could find,maybe just good practise instead,check selection and erection as there are a few regs about the installation of the cables ie ingress of water,poor connections etc,hope this helps.

 

[pushrod]

Where an inner core of SWA is being used as the cpc the armouring is an extraneous or exposed conductor and requires supplementary equipotential bonding and connecting to the protective conductors. See reg 415.2.1 (page 59).

 

[andyb]

The armour of an swa cable is an exposed conductive part no matter what, and as such has to be connected to the main earth terminal of the installation.

 

[Davey101]

Thanks lads. Just to clarify, the 1st light is earthed, from the D/board/trunking, the rest of them are not, due to the lack of banjo's. I cant remember seeing an SWA which wasnt earthed either, and have never really worried about a reg before. Perhaps they havent put a reg in cos its so obvious.

I was just looking for a specific reg, as I had basically been asked to prove it was necessary.

Cheers, Dave

 

[pushrod]

The armour of an swa cable is an exposed conductive part no matter what,.

sometimes it is the CPC - I was just providing a specific reg No. that the OP could use to prove his case.

 

[robsparky1975]

yes reg 415.2.1,i would agree with everything about that,the regs are not clear enough in what it is trying to achieve at times,there has been speculation on new 18th edition next couple of years,but i bumped into college tutor who ran our 17th edition and its not true,there was a corrigendum(latin for printing error i think) in july 2008,its quite minor errors 4 pages and you adjust the errors by hand,there is going to be a 2nd amendment(reprint) next year im told,they make these books that then have to be made explainable(on site guide) and maybe further more the electricians guide to the regs(oh come on iee this must be saying something).

 

[Guest123]

Armour is definately classed as an exposed conductive part when not used as the CPC therefore must be earthed.

As has been previously stated if protection against indirect contact (fault protection) in new money is by ADS then all armouring must be connected to earth.

Another situation that may arise in certain conditions is induced voltages and/or EMF which may cause overheating of the cable should the armour not be connected to earth.

Also as a previous poster mentioned any spare cores should also be connected to earth as volatges may also be induced into them.

 

[electricAl]

I`m sure we can all relate to the OPs dilemma - many of us have been put on the spot & forced to either pull a Reg # from thin air or forced to back down.

The problem here is, the need to earth (or even bond - if you`re being finnicky) the armour is so obvious to any one electrically educated, that finding a particular line that says we should, has never been needed. Anyone with half a clue would know it needs doin.

In the same way that we wouldn`t fire through a live submain with a pair of boltcroppers.

I stand to be corrected, but i can`t recall a specific reference in the BRB, or elsewhere, that tells me this should not be done. There isn`t even a recommendation not to do it in the EAWR. Nor the HSE documentation i have at hand.

I sympathise with Davey`s predicament, but many have looked fruitlessly, and ultimately he`ll have to just stand up & tell em the truth - its so bleedin obvious no-one felt it necessary to write it down.
Like climbing up a tree in a thunderstorm, or sticking your hand in a bucket of plaster-of-Paris...



Sorry Mac & other shamrockers - shouldn`t have mentioned that place so soon

 

[skirby]

I have come across this quite often on testing.

I think you chaps have pretty well covered everything, but here's my take on it:

I would consider the steel wiring of a swa cable to be a conductive part (and also an additional cpc).
The armouring may be covered by pvc insulation but the brass cable gland is exposed inside the plastic fitting and the shroud could slip back.

543.2.5, 6 & 7 refer to cable sheaths and connections to earth.

My opinion is that swa armouring must always be earthed (at least at the supply end).

To not install an earth connection is bad practice which I would put down to lazyness or ignorance on the part of the installer.

When testing I would give a code 2 indicating that a potential danger exists.

 

[andyb]

411.4.2 Each exposed-conductive part of the installation shall be connected by a protective conductor to the main earthing terminal of the installation,