Terminating_SWA wiki... some thoughts

Looking at the Terminating_SWA wiki it could do with some improvements.
Types of gland. - BW - Internal use only (B) - CW - External use with sheath seal (type C) - E1W - External use with sheath seal & bedding seal (type E)
External SWA gland failures. Life of SWA cable is dependent on the life of the armour which is governed by two factors 1) damage to sheath 2) water ingress at glands. Any water ingress by either method will first erode the sacrificial zinc plating (evidence of a white zinc oxide paste), then quickly corrode through the steel armour (evidence of rust and eventual failure). Water ingress will first degrading then destroy the ability of the armour to act as CPC.
Damage to sheath can be avoided by burying at sufficient depth for the land, bedding & coverage with river washed sand (150mm nom.), electrical cable below marker tape on top, area free of stones. Surface stones will migrate through clay over time, so the Rockery you forgot about may have become the Rockery of Atlantis. Underground conduit may be used, the ideal being twinwall which offers a smooth wall easing the drawing in of a replacement cable.
Damage via water ingress at glands is rare, but can occur and may be extremely costly. A conventional CW gland seals only against the sheath, there is no seal against the bedding. If the enclosure permits any water ingress then moisture will accumulate at the lowest point - firstly around the armour cone & secondly along the cable itself between bedding, armour & sheath. SWA armour provides only 92% coverage so permitting water migration along the cable by gravity & capillary action. The first sign of water ingress is often a zinc paste around armour strands in the cone, stripping back the sheath can reveal once shiny zinc plating is now tarnished with corrosion. Eventually a crunching sound can be heard as the SWA is bent (cue argument for 25A EFLI fault testing in place of rather than 15mA connection exists testing).
Water ingress at glands may be reduced by 1) use of an E1W gland which provides a seal against the cable bedding, thus sealing cone-armour & cable armour from water ingress into the enclosure; 2) the enclosure may be "potted" with a re-enterable material - eg, Magic Gel (pourable), Magic Gel Block (squishable, eg, BESA/conduit boxes) or Bicon/Prysmian R391 non-setting weatherproofing compound (putty). Potting material must be re-enterable unless crimps are used so as to permit Inspection & Testing. Where plastic enclosures are used with SWA it is important the enclosure seal is not compromised by the weight of the SWA cable or cable cleating - correct cleating will transfer no load to the enclosure.
In extreme circumstances there remains an inherent weakness even with E1W glands - that is the thread of the cone-nut can permit water to be drawn in and attack armour over time. This is common in offshore usage and requires use of a Deluge Gland (DTS01) which specifically exclude this means of water entry. It can however occur where either CW & E1W glands enter the bottom of a malleable iron conduit (BESA) box such that the shroud permits water to pool. The shape of a BESA box naturally channels water to the shroud and the shroud has no natural horizontal sealing surface as with a conventional enclosure. A solutions may be to 1) put a small quantity of silicon grease on the cone-nut threads 2) put a small hole in the shroud (effect drainage) or 3) fit a large washer (M20 type C) above the gland to provide a horizontal surface for the shroud to butt against. Silicone must not be used as the gland dissassembly is required for Inspection & Testing. BESA boxes can permit water ingress via lid distortion during tightening against the gasket.
One other benefit of E1W glands over CW is a longer (typically 15mm) thread length. When plastic enclosures are combined with Pirana/ Earthing nuts the wall thickness can render the CW 10mm thread insufficient.
Obviously as one gets closer to underground applications, such detail in gland selection & installation becomes paramount.
Gland sizing with 1.5mm. SWA 1.5mm 2c & 3c SWA can vary with respect to outer sheath diameter, armour wire diameter & bedding diameter. This can result in some CW 20s glands failing to seal the small diameter outer sheath (water ingress) or failing to grip thin armour wires (armour pullout). If this is found a 20ss gland may need to be used.
Sealing washer. CW & E1W glands only achieve an IP66 seal if fitted with a sealing washer. Examples are nylon, red fibre & PTFE.
Gland shroud. Where PVC shrouds are found to degrade, PCP shrouds provide better UV protection & sealing. This is unlikely to be an issue for the UK climate even if south-facing.
Putting shroud on. Cut the end of the SWA cable square by saw/cutters, pull the shroud down onto the cable end, cut the shroud square with a knife - using the deformation around the cable end as a guide.
Cutting the armour. Side cutters may be used, but it can be difficult to achieve parallel cuts around the perimeter of wires. Copper pipe cutters with hardened wheels can be used to score the armour wires, which is then flexed & snapped ensuring a parallel cut. Dedicated SWA cutters exist to achieve same.
Stripping bedding off. It is not advisable to cut the bedding circumferentially with a knife: with certain wire sizes (eg, 4mm) and core counts (eg, 5c) the bedding may be extremely thin increasing the risk that the knife penetrates to damage core insulation. Most bedding materials on recent cable are extremely soft material and can easily be torn by hand from the end - either longitudinally or circumferentially. This avoids any risk of core insulation damage. It is advisable to leave a small length of bedding protruding from the gland to protect the cores from abrasion during wiring/maintenance operations.
Earthing. Where a plastic enclosure is used, earthing is dependent on the integrity of the enclosure remaining. This can be avoided by use of a Piranha/Earthing Nut which is locked onto the gland thread by a grub- screw so providing retention even if the enclosure is damaged & preventing loosening of the nut.
TT Glands. Where an SWA cable supplies an outbuilding (garage, shed) which has a TT supply (local earth rod, house PME not exported) a problem arises whereby the SWA gland metalwork is itself earthed to the armour thereby introducing PME potential metalwork into the TT environment. The readily removeable shroud is not considered an insulation. A solution is to use a hard plastic covered SWA gland - eg, CCG IP68 or Bite SWA glands. Use of such glands avoids the need to use a non-SWA stuffing gland on the outside of an enclosure, only to leave the SWA wires inside.
Someone may need to check the last bit w.r.t. 17th - as the gland threads inside will be exposed (could heatshrink), but are only accessible via opening the enclosure which should require use of a tool?
Just some thoughts - personal opinion.
Seen a lot of CW gland failures recently - perfectly made, all suffering from a) water ingress into the BESA/plastic enclosure condensing in the armour cone or b) SWA made off into BESA boxes now suffering from cone-nut water ingress. I'm suspicious of modern cone- nut threads being so poor they permit water supplied via the inside of the shroud to be drawn in by capillary action and heat/cool cycles of the enclosure.
Might check if an M20 Type-C? washer would provide a horizontal surface for the shroud to butt-up against when SWA CW glanded into BESA boxes, off to Google as that would be a dirt-cheap fix.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
js.b1 wrote:

Yup, I must get round to doing some more photos for it as well...

Not used the E1W type myself - it does sound like a better construction though.

Yup, prolly worth adding.

Might be better to add this bit in the outdoor electrics article - since its not really specific to terminating the SWA but is instrumental to the larger picture.
We have a bit on it here:
I will add the comments on twinwall to the ducted section.

Good argument for keeping old megger LT5/6 testers and similar as well... the "non tripping" may be ok for their intended purpose, but don't give anything like the same stress test.

Must admit to not having had that problem - but then again perhaps I have never encountered a particularly thick walled enclosure.

Yup, this is one that needs more photos. The method description is ok, but the photos don' really illustrate the easier options like the wheel cutter or the bespoke tool (which I must admit I find well worth having, since it is quite a bit faster than any other method I have tried so far).

Agreed, more description would help on this bit... the ring with a knife technique works ok on the fairly hard bedding you sometimes find (especially on that 'orrible hi-tuf bedding!), but you don't want a through cut - just enough nick to allow it to break on cue.

There was a discussion about this a while ago IIRC.

The CCG seems like an elegant solution to that one....

I suppose you would have to be fairly unlucky to have your fingers in the TT enclosure at the same time as having a floating PEN fault on the head end supply.

Many thanks for them. It all helps refine the quality of the articles.



  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.