Regardless of whether the armouring of a steel wire armoured cable (swa) is employed as a protective conductor or not, it should always be effectively earthed to ensure the requirements of ADS are met.

Where swa cables are connected to metallic enclosures, such as items of switchgear and control gear that also serve as the protective conductor of the circuit concerned, all the requirements of Regulation 543.2.2 (relating to the suitability of a metallic enclosure to provide effective earthing), should be met.

Where cables are terminated into enclosures such as consumer units and distribution boards, it should be confirmed that the connection at the interface between the steel enclosure and brass gland, as shown in Fig 1, is mechanically and electrically sound.

Many steel enclosures are coated with finishing products, such as epoxy resin or powder coated paint, to protect them from corrosion, but as such coatings are generally non-conductive they are likely to act as a barrier at the interface connection, between the brass gland and the steel enclosure. As a result, the resistance value of the armouring may be increased beyond that acceptable to meet the requirements of ADS.

To ensure a low resistance connection is achieved between the steel wire armour and the steel enclosure an earth tag washer (‘banjo’or earthing nut) should be included in the gland assembly, as shown in Fig 1.



Where swa cables are terminated into non-metallic enclosures, such as for example where an isolating device for a piece of fixed equipment is comprised of a non-metallic enclosure, the continuity of the armouring should be maintained across the enclosure by the use of earth tag washers and an attached adequately sized conductor, as shown in Fig 2.

The connection should be made by fitting the appropriate size of cable gland in accordance with the manufacturer’s instructions, and ensuring the cable is adequately supported to prevent undue strain on the gland connection (Regulation 522.8.5 refers).

Bends in swa cable should comply with the minimum values recommended by the cable manufacturer based on the cables overall diameter. Otherwise, damage may be caused to the armouring, conductors, or the cable insulation during erection of the installation or at some other time, such as under fault conditions.

It should be noted that non-metallic enclosures may be used for the purposes of divorcing one earthing system from another, such as where it is desired to arrange a TT earthing system from a TN-C-S supply.

The minimum radius dimension calculated from the table shown relates to the surface of the cable on the inside of the bend (see Fig 3) and can be calculated in terms of the overall diameter of the cable.

As an example, consider an armoured thermosetting insulated cable having copper circular conductors and an overall diameter of 32 mm.

From the table, it can be seen that the recommended minimum internal bending radius for the cable is six times its overall diameter (i.e. 6 x 32 mm = 192 mm). Had the conductors of the cable been of the copper shaped type, the minimum recommended internal bending radius would have been eight times the overall diameter.

British Standards for cables recommend that for a cable having a standard thermoplastic (pvc) sheath, installation (including bending) should take place only when both cable and ambient temperature are above 0° C and have been so for the previous 24 hours, or when special precautions have been taken to maintain the cable above 0° C.

While identification of the armouring is not required (Regulation514.6 refers), the cores of swa cables should be identified using:

The bi-colour combination green-and-yellow shall be used exclusively for identification of a protective conductor and this combination shall not be used for any other purpose (Regulation 514.4.2 refers).

This article will discuss the identification of extraneous-conductive-parts to avoid the unnecessary installation of protective bonding conductors and the potential introduction of hazards.

NICEIC has produced this guide covering the risks that need to be considered when mounting electrical equipment in loft spaces in domestic premises.

The technical experts at NICEIC have created this guide to the appropriate use Minor Works Certificates.

Good article, but there is no mention made of the common method of dealing with the coating on the steel enclosure, which is to scrape off the paint at the connection point. May be fine for immediate testing, but surprise, surprise, when you come back to it after a couple of years the connection is rusted and useless. More time spent in doing the job properly will reduce the time that can be charged for remedial work, but is the safe way to do it.

A smear of petroleum jelly will prevent the oxidation. Also it is common practice for brass glands to be supplied with galvanised locknuts which contravene the I.E.E.Regulations. The action of 3 dissimilar metals is bound to cause corrosion. The worst offending metals are stainless steel touching galvanised steel.

Where a protective coating against corrosion has been removed from a ferrous metal enclosure for earthing or otherwise, it should be made good with a protective coating of paint on completion of the work. Grip marks, conduit runners, scratches, and the like would be painted by any properly trained electrician worth his salt.

The reality is that the thread on the gland is short and incapable of being done up tight , modern glands with energy saving poor quality brass mean that the outer armouring is now just that and we only need it to be tested at install so we can get paid . Try asking for a decent brass bush or gland ?

I agree with you 100%, the gland manufacturers should be made to comply with this as often times the gland plate is a thick aluminium and you can just about fit the plate lock nut

Use a coupling and a male brass bush to accept the gland. Note. To prevent any oxidation use a smear of petroleum jelly (Vaseline) after completing the glanding.

For years its been overlooked that terminating armouring each end of two boxes and it does not matter if insulated or metal that if the cable has a cpc that the load end armouring should be insulated from the box. The earthing should be the cpc. The armouring should be the mechanical protection and earthed one end only at the supply. The forward end insulated. Why is this not good practice ? Please advise.

This practice determines that any earth fault current is routed to the main earth point and not allowed to circulate through all the earth paths available.

I've never relied on armor as the CPC, I see it as bad practice. You just cant rely on the integrity of the armor as the CPC over the life of the cable. I've often pulled old cables out of the ground only to find at some point the outer insulation has been penetrated and the armor non existent.

Add the fact that most gland threads these days are too short to attach 2 lock-nuts to the struggle to make sure that both are tight enough, I will always go for one lock nut tightened correctly, and a brass nut and bolt drilled through the enclosure with earth lug attached internally.

I agree that the steel armouring should be connected to earth but really only to ensure that if the cable becomes damaged i.e. a garden fork in pushed through it, any contact with live will result in a circuit trip. I believe that for correct CPC there should be a separate core used specifically for this. With respect to the earthing tag, I find it better to solder the earth wire to this or use an earth locking nut such as the Piranha products as long as there is sufficient thread available on the gland.

As I understand it, metal conduit was the circuit protective conductor. Hence the need for mechanical soundness to promote electrical continuity. Accessories were earthed via the conduit. Times have changed.

I agree with the comment on not relying upon the amour of the SWA as the CPC, after all it's sold as armoured cable not 'cable with an wire armour that can also be used as a CPC' cable! However I have come across install's with the armour bunched up into a block connector and then connected to the CPC! That makes for a interesting 'jam packed' adaptable box!!

I always thought swa refered to "single wire armoured" as opposed to "steel wire armoured" and dwa in the same vein "double wire armoured"

All comments show that most serious hands on engineers know the right solution and care for safety. It is a fact that most swa glands in market do not really comply to regulations and are of poor quality. Therefore because no authority inspects these product it relies to the engineer for the application of safety, generally speaking. However it is a great advantage using this site for the exchange of experience and suggestions. Have a nice day. From Larnaca-Cyprus :-)

There are lots of options. TP+ N cable Br/Bl/Grey with or without a neutral. Consider: 1. Br/Bl/Grey for a balanced load using armouring for a CPC as well as mechanical protection. 2. The same as 1. with a neutral for unbalanced loads. Yay! Usually this option requires a separately run CPC with the armour acting as an auxiliary CPC as well as mechanical protection. 3. TP+N cable is often used for SP+ N+E. Again, the armouring is usually ancillary.

As some posts point out, usually there is found bad terminations of glands across the board. I personally subscribe to the part in the regs. where it says; Mechanically sound, electrically continuous. In this day and age, practices make this difficult to maintain.

This is o.k. at the ends of a cable. But what about the rest of the cable if it goes underground? 60 years experience dictates that although the armourings have to be earthed, NO reliance should be made on these armourings as the sole means of providing a cpc.

Also the armourings on instrument cables should only be unearthed at the "Sending" end of the cable in order to reduce eddy current pick up in the cable.

SWA is steel wire armor. The steel armor at a minimum should be earthed at distribution end. This earthing is in case the cable is damaged, the armor is never used as the earth on the circuit. If the cable is being glanded at one or both ends the method of putting the earth tag inside enclosure and bending same to connect bonding. The method of drilling enclosure to attach earth strap is no longer used in Ireland. There are different specifications of SWA glands available and yes they cost alot more but are worth it . The importance of earthing cannot be underestimated. It should be be the first cable connected, the last cable disconnected and the longest of all cables. This ensures if the cable is pulled and the armor earthing is compromised there still remains an earth, and if cable gets pulled then the earth as the longest cable will be the last cable to be pulled- thus ensuring safety, and most likely the phase/s will short against a still earthed piece of equipment and will blow/trip associated device ( assuming good discrimination)

Maybe its just the way you wrote it but I think you might be confusing "earthing" with "bonding" .... both look similar to the untrained eye but are very different animals in practice.

YEP, piss poor installs due to poor/no training in SWA or Pyro. I put it down to Part P (Pretend ) electricians. I think 2 core should be banned/not used. CPC/SWA should be connected at far end so that RCD/RCBO works. Use Banjo dril/bolt to box or piranha earth nut.

Some interesting, and very applicable comments .. I grew up on the 14th Edition where the metallic enclosures / conduits / armouring etc.. were the 'earthing' (sorry CPC in new money!). Increased resistance (sorry, impedance!) from steel products as they age will always on conductivity, so require remedial work 'down the line'. At least with copper, or aluminium current carrying conductors, their resistance should be constant, so I've always subscribed to the view of using a circuit conductor as the CPC. The other big consideration not previously mentioned is the physical fact of all dissimilar materials having a different coefficient of expansion, so a steel enclosure and brass gland / locknut will eventually 'move' from each other at different rates, increasing resistance. We know that terminate a copper conductor in a brass terminal 'up tight', then go back in 3 months, and you'll be able to 'nip it up' perhaps a quarter turn! The point made by many about the threaded length on SWA glands is very valid, and I would argue with the gland manufactures about their product 'being fit for purpose'? - no offence! happy new year :-)

Armour should not be relied on for earth Now we in brexit and out of european rubbish colour codings should be returned to bss Red yellow blue phases Black neutral green earth

I have used sea for 40 odd years and have always specified a three core for single phase and 5 core for three phase. To put your trust in the armour is madness as it can be too easily damaged or worst case the end not made off properly which can result in significant danger being present

I discovered a joint in a new installation between a 3 core SWA cable and T&E with strip connectors stuffed inside a plastic trunking with no connection at all to the armour. It was made by an electrician who claimed did not understand why anything was wrong.

I discovered a joint in a new installation between a 3 core SWA cable and T&E with strip connectors stuffed inside a plastic trunking with no connection at all to the armour. It was made by an electrician who claimed did not understand why anything was wrong.

I agree that SWA cable glands are of poor quality and are barely fit for purpose. I personally use glands manufactured for use in the hazardous area industry. The only down side is the cost, about four times that of a standard gland. There is plenty of thread, the clamping and sealing properties are far superior.

Having read all the comments there has been no mention of serrated washers, these are effective in the connection and also maintains the locknut remains tight. I would still rather see an internal earthing core as opposed to swa been the continuity of earth.

Agree and particular the last comment about serrated(star) washers which remain mainstay for product safety earth bonding. The SWA must be earthed as a protective measure should an eager digger slice or break the cable the earth fault should trip. Not sure that is mandated that ELCB must be used to protect the cable? The addition of a star washer removes the requirement for the double lock nut which would only be required if the enclosure were plastic. with a metal enclosure it would assrmble as gland; enclosure; star washer; earth ring; lock nut

I find that most wholesalers now do not keep 2 core SWA if you ask for it it's usually more expensive than the 3 core so I agree it's a much better job to use the 3 core.That said you still need to earth the armouring, we have been using the earthing lock nuts for some time now which is much easier than earth tags they have a cutting tooth on the one face to dig in the same as serrated washers.I found that buying the gland pack's complete is the cheapest option.I am sure I seen many year ago a hole saw that had a serrated cutting flange at the back which was designed to remove the paint from the knock out holes but tried some time ago to find one with out success. Does anybody know if they are still available if not perhaps a manufacture should start making one this would make removing the coating a lot easier and a neater job.

I buy internally serrated washers and connect earth at user end only. This means with metal units no need for banjo and RCD/RCBO at supply end trips. If you earth at supply end only, RCD may trip but induced volts at user end make it dangerous.

Crimp Couplings Work

Originally posted July 2017 and repeat as I do not think that those concerned got my question and repeat, but in a different way - For years has it been overlooked by the Regs that terminating the armouring to an earth at each end of an armoured cable – Especially if the cable has a CPC, which may cause circulatory currents to flow and increased corrosion or incorrect tripping. Armouring should be the physical protection of the cable and earthed at the supply end to reduce induced voltage. If connected at the load end also will this cause issues. The earthing and any faults should be dealt with by the cpc. The armouring should be the mechanical protection and earthed one end only at the supply end. The forward end or load end to be insulated. Why is this not good practice ? Agree with comments about glands and can only suggest that gland thread length are sized to box plate thickness plus enough length for nut, washer and brass tag. Multi-stranded cables are best lugged and or crimped.

I purchased some 20scw glands from a supplier in Barnsley only to find that the manufacturer had reduced the body diameter from 24mm across the flats to 22mm. They are noticably smaller (and of course cheaper to make) but the sealing face to the enclosure is so small that normal 20mm sealing washers for IP rating cannot be used, they do not form a continuous sealing face.

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