Earthing SWA at both ends

[GEOFF S]

Personally, it depends upon the use of SWA as to whether the armour needs earthing, its good practice to earth it in my opinion.

What happens if the basic swa insulation fails, is there any supplementary insulation? The bedding of SWA is PVC, are the live parts of this cable any worse than that of T/E. Is there any supplementary insulation between cpc and basic insulation in T/E?

Cheers

 

[telectrix]

Of course it's obvious, the metal back box cannot normally be touched, without the use of a tool and the removal of earthed screws, whereas the armour can be touched simply by sliding a gland boot down. Something that can occur without human intervention.

but once the faceplate fixing screws are fitted, it then becomes "exposed".

 

[stevethesparks]

Personally, it depends upon the use of SWA as to whether the armour needs earthing, its good practice to earth it in my opinion.

I would say its imperative to earth the armour of an SWA.

What happens if the basic swa insulation fails, is there any supplementary insulation? The bedding of SWA is PVC, are the live parts of this cable any worse than that of T/E. Is there any supplementary insulation between cpc and basic insulation in T/E?
Cheers.

T&E and SWA can't be compared, either are chosen to suit the design of the installation

 

[GEOFF S]

I would say its imperative to earth the armour of an SWA.

T&E and SWA can't be compared, either are chosen to suit the design of the installation

I think your missing my point, look at the definition of an exposed conductive part, it states basic insulation, swa has basic and supplementary insulation.

Does the armour need connecting to earth, in many instances but not all.

Cheers

 

[davesparks]

I think your missing my point, look at the definition of an exposed conductive part, it states basic insulation, swa has basic and supplementary insulation.

Does the armour need connecting to earth, in many instances but not all.

Cheers

It always needs connecting to the earthing system of the installation it is fed from.
One purpose of the armour is to connect any metal object penetrating the cable with earth before it makes contact with any live conductor.

 

[stevethesparks]

It always needs connecting to the earthing system of the installation it is fed from.
One purpose of the armour is to connect any metal object penetrating the cable with earth before it makes contact with any live conductor.

Precisely

 

[GEOFF S]

It always needs connecting to the earthing system of the installation it is fed from.
One purpose of the armour is to connect any metal object penetrating the cable with earth before it makes contact with any live conductor.

Okay, lets say we use swa instead of T/E surface mounted, there is no requirement for an earthed sheath, just because its there, where in the regs states it must be earthed, Reg numbers?

If the basic insulation fails Dave, will the armour become live or will the supplementary insulation prevent this. So how does it meet the definition of an exposed conductive part, any Regulation numbers would be good?

Now if the cable is buried, thats a different matter.

So surface mounted, into plastice enclosure via plastic gland, boot over end of cable protecting ends of cable within enclosure. What are the Regulations requiring the armour to be earthed?

Cheers

 

[davesparks]

Okay, lets say we use swa instead of T/E surface mounted, there is no requirement for an earthed sheath, just because its there, where in the regs states it must be earthed, Reg numbers?

If the basic insulation fails Dave, will the armour become live or will the supplementary insulation prevent this. So how does it meet the definition of an exposed conductive part, any Regulation numbers would be good?

Now if the cable is buried, thats a different matter.

So surface mounted, into plastice enclosure via plastic gland, boot over end of cable protecting ends of cable within enclosure. What are the Regulations requiring the armour to be earthed?

Cheers

What supplementary insulation? The conductors are insulated, they are then bound together with tapes or an extruded bedding, armour laid over that with an outer PVC serving.
There is only one insulation layer.

It is not an exposed conductive part, I have never suggested it is! But the cable is designed to be installed with the armour earthed, if it is not then it is not being installed as it is intended.

The cable is designed, tested and approved for use under the British standards referenced in bs7671. That approval will have been given with the armour earthed as it was designed to be.

 

[Dave OCD]

No at the very least on smaller sizes of SWA there is definitely a solid insulating sheath external to the insulated cores !
So IMO that is insulated AND sheathed.

 

[davesparks]

No at the very least on smaller sizes of SWA there is definitely a solid insulating sheath external to the insulated cores !
So IMO that is insulated AND sheathed.

Where?
The sheath is not insulation on standard swa

 

[Dave OCD]

Well I've stripped hundreds of SWA ends and the material under the armour is just like the sheath of flex, and it's not conductive is it ?!

 

[davesparks]

Well I've stripped hundreds of SWA ends and the material under the armour is just like the sheath of flex, and it's not conductive is it ?!

The bedding? It's carries no insulation rating whatsoever, it's purpose is to give the cable shape and prevent the armour coming in to contact with the insulation of the cores.
You say it is just like the sheath of flex, which particular flex are you referring to? I can't think of any flex which has a sheath that soft. It's irrelevant anyway as the sheath of flex is also a sheath and not insulation

 

[Dave OCD]

Well we must be using versions of SWA from different universes Dave. :confused5: I'm thinking 1.5/2.5/4/6mm 3core , and that sheath is as tough as flex sheath.

 

[davesparks]

Well we must be using versions of SWA from different universes Dave. :confused5: I'm thinking 1.5/2.5/4/6mm 3core , and that sheath is as tough as flex sheath.

Yes the sheath is as tough as some flexes, less tough than some and more tough than others. It does not make it insulation though!

It is not tested or rated as insulation and so from a technical standpoint it cannot fulfill the role of insulation. If you carried out voltage withstand testing on the sheath as of it was insulation it would fail!

 

[Dave OCD]

I'm not so sure.:wink5: