Earthing SWA at both ends

[Leesparkykent]

The bedding is Generally made out of polyvinyl chloride (pvc) which is the same as the Sheath.

 

[Dave OCD]

Precisely !

 

[GEOFF S]

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.

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 the Extruded bedding compound used by cables to BS5467 is PVC, are you suggesting this has no insulating properties?

So there is no requiremnet within BS7671, i have various Manufacturers data, where are you finding reference to the armour requiring earthing, which manufacturer?

Cheers

 

[davesparks]

Dave the Extruded bedding compound used by cables to BS5467 is PVC, are you suggesting this has no insulating properties?

So there is no requiremnet within BS7671, i have various Manufacturers data, where are you finding reference to the armour requiring earthing, which manufacturer?

Cheers

Yes it is sometimes PVC, it can also be a string and tape but this is less common these days. but it is not tested or rated for any voltage withstand.

 

[Leesparkykent]

Yes it is sometimes PVC, it can also be a string and tape but this is less common these days. but it is not tested or rated for any voltage withstand.

What PVC?

 

[davesparks]

What PVC?

Yes, not all PVC is the same! The bedding and sheath are both made of PVC, if you have a proper look at it next time you strip some you will notice that it's not the same. The density, strength, flexibility etc are different due to a lower grade (cheaper) being used for the bedding than for the sheath

 

[Deleted member 26818]

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

So by using screws which are earthed via the faceplate, the back box becomes exposed requiring a fly lead to connect it to the face plate so it can be earthed?

 

[remer1957]

I always connect the earthing fly lead to back boxes I install, it's easy to do if done before installation of the box, takes 10 seconds and 4 inches (100mm) of earth cable. In fact, I used to carry pre-cut lengths of cable for just this purpose. I also earth both ends of the SWA, it doesn't take long and I think it's good practice.

 

[shanky887614]

I always connect the earthing fly lead to back boxes I install, it's easy to do if done before installation of the box, takes 10 seconds and 4 inches (100mm) of earth cable. In fact, I used to carry pre-cut lengths of cable for just this purpose. I also earth both ends of the SWA, it doesn't take long and I think it's good practice.

thats a good way to do it, earth lead when you first fix i mean

 

[Deleted member 26818]

thats a good way to do it, earth lead when you first fix i mean

Yep, some of the boxes I've been 2nd fixing have 2 or 3 extensions, can't even see the earth lug.

 

[shanky887614]

Yep, some of the boxes I've been 2nd fixing have 2 or 3 extensions, can't even see the earth lug.

lol must have had the same plasterer, ive used 75mm 3.5mm pins and 3/4 extension pins lol

 

[Dave OCD]

lol must have had the same plasterer, ive used 75mm 3.5mm pins and 3/4 extension pins lol

Plenty of wiring space though.

 

[Risteard]

As stated the bedding (although it may be made from insulating material) is not tested as insulation. Likewise the sheath of T&E; flex etc. is not tested as insulation.

That is not its purpose.

Also, in an SWA the bedding is not intended to be used as a sheath, so couldn't be run free as an insulated and sheathed cable, as it isn't and therefore must be within the enclosure if the sheath and armour has been removed.

 

[Big Sausage]

Certain industrial installation designs require that earthing systems are separated from source supplies due to the requirement to maintain a "single point earthing system".
For example some signalling rooms on railway installations are provided with a earth that forms part of the signalling system and is totally separate from the main supply earth.
Typically the design for those installations will specify that the sub-main SWA cable supplying that location is only earthed at the origination of the supply and that the load end is terminated in to a "insulated cable gland".