Testing SWA

[jeremy]

What if , right, you've already got 50m of 2 core and you've promised to do your cousins garden lights cheap? If you're worried about degradation , WD40 doesn't hurt on the armour, a liitle bit of mastic etc. And you would have to be especially gifted to cut through the armour enough to give you an earth free path to a live conductor without getting enough earth path through your spade or is it ceramic? I'm only messing!!

 

[tigerpaul]

What I have been doing, and has been accepted by many companies I've been testing for, is I write "SWA" in the cpc column of the test sheet instead of a conductor size.
In the cable type coloumn I write "F" for PVC/SWA or "G" for XLPE/SWA.

It is good practice to use a 3 core SWA now and utilise one core for a cpc, but I dont think there is anything wrong with using the armouring of a 2 core cable for a cpc as long as it is fit for purpose, ie check old cables for signs of excess corrosion.

If someone was to cut the cable, and the blade was to go through the armour into the live conductor first before going into the cpc a dangerous situation would occur. So you need to bond the armour of a 3 core cable to provide the earth path, even if your not using it as the actual cpc.

 

[uksel]

I take your point, but if you run a SWA underground (say 3 core and each core is used as a line conductor) and someone goes though that with a saw, (seen it a few times when people have foundations dug out for a conservatory) then that cable will still be live, not trip the Protective device and becomes a hazzard to the poor bugger you grabs the end of it (if not already had a shock from saw). Where as if the Armour was earthed then the protective device would trip preventing the risk of shock.

The seperate earth would only provide an earth at the other end, but so does the armour. if the ends are terminated properley then there shouldnt be any moisture ingress, and the cable (inc earth continuity) should has as long as the installation

you've got this totally wrong mate, the armouring MUST have a good connection to earth, through the glands, which, if not connected directly to earthed metalwork, then you are required to ensure continuity must be maintained by using a brass banjo. (I also like to use serrated washers to dig into any metal casing to give a good connection).

what the discussion is about is; wether the armourings can/should be relied on for the only means of earthing, armourings and the glands can be considered exposed conductive parts which also requires they be earthed regardless.

also you quoted "if the ends are terminated properley then there shouldnt be any moisture ingress"

shrouds are not always perfect, and if connected outdoors any bangs or bumps could expose the armourings to the elements. but the consideration should not just be fo the ends, what you'd have to consider is, if someone did give the cable a clout it doesn't always take a lot to remove a bit of the sheathing, the tiniest nick could let in water and cause the armourings inside to deteriorate. i've changed loads of SWA which have had water ingress regardless of how good the connections were at the gland

 

[flukey]

Perfectly ok to use armour as circuit cpc as long as conforms with big red book

 

[jeremy]

I'm with the flukey dude. you can only do an install to the best of your ability. you have no way of knowing what some eejit is going to come and do to your lovely tidy install. If the book says "yes" then someone else has made the decision of wether it's acceptable or not. Obviously a bit of common sense needs to be applied. !

 

[uksel]

i guess it's each to their own, but i don't think i'd be running SWA without a dedicated CPC, just what i was taught i guess

 

[Paul_Rawlinson]

The electricity board relay totally on the armour in a TN-S system and TN-C-S sysyem. Regs say its fine so really cant see the problem with using the armour as the sole means of earthing.

 

[WarrenG]

Cut through with a metal shovel whilst digging

 

[hughesy]

ive seen allot of sparkys write (sheath) where you would normally write the size.makes sense to me as the armouring is a sheath.

 

[coxy]

HI,
The nic have a guide for this within one of their books.I had the same problem recently on a periodic test.The flats were built early 1980s and 2 core swa was used.It turns out that 16mm 2 core swa is equal to a 10 mm earth on the armour.I agree we would not rely on this now but my loop readings were fine so could not fault it.I also contacted the manufactors of the swa who confirmed the same.

 

[actionjack]

I am afraid Uksel has got it completely wrong, Paul is correct.

 

[jamie968]

is it possible to cut live 300mm swa cable?:

 

[Eggster71]

is it possible to cut live 300mm swa cable?:

Yeah, with a big digger, an axe, reciprocating saw or kango I suppose?

 

[UNG]

NO NO NO - i believe you are very wrong there!

the armouring is not designed to be relied on as an earth connection!

the armourings reason for being there is to offer mechanical protection, end of - the earth connection is a benefit. the armourings are there to try and protect the cable from being cut through, which is why you use ARMOURED cable! armour is armour, earth is earth

i'm not saying it can't be used, it is (i believe) good practice to ensure if there is no core to be used as an earth then a seperate earth will be run. the csa of the armourings meets the requirements of the regulations (unless you start using single cores or two core SWA with conductor CSA's of greater than 120mm)

whilst it may be adequate on installation, with 5 years of degredation (depending on the environment) it could easily break down/rust at the glands or any breaks or water ingress into the pvc sheath.

if it's possible i'd always run a seperate earth, and it is in most circumstances i think reasonable to do so

I'm a bit confused
Two different views in two posts, So do you always run a separate CPC or do you sometimes rely on the armour even though you appear so against it

 

[Eggster71]

The selection and erection guidance note (don't have it here so can't remember specifics) tabulates most pvc and xlpe armour sizes and also states if the armour is adequate for use as the cpc without a parallel cable.
As far as I'm concerned if the CPC is run as a core within the cable I'll bond one end of the cable with a bolt and banjo, if the armour is to be used I'll banjo it and flylead it BOTH ENDS with a cable of a suitable size for a cpc so for the sake of argument 6mm/2.5 is standard T&E then a 2.5 single will be adequate as a flylead for a 6mm SWA.