De-sheathing SWA

[jpadie]

Hello

 

Is it normal/acceptable practice to remove the outer insulation and armour and gland off SWA into a small junction box once it gets inside the premises and run the rest of the distance to the consumer unit with just the internal common insulation?  No joins but then the bend radius would be a lot more manageable for the routing that will be needed.  

 

The armour would be earth bonded at the main consumer board gland (ie the other end to the one I'm worried about.  This is 3 core SWA so the third/grey core will be used as earth to the sub-consumer board)

 

Thank you

Justin 

 

 

[ProDave]

Are you talking of doing this at the source end, or the destination end?  It is not clear.

 

If at the source end then where you gland the SWA you would also have to run an appropriate size earth cable along with the inner cores to the consumer unit so the SWA is bonded at the source end.

 

Remember no armour on that internal section would mean the cable routing method would have to be appropriate for whether there is RCD protection or not. which would probably preclude it being buried in a wall.  It is common to feed an SWA without RCD protection and provide that at the destination end.

[jpadie]

On the destination end.  Sorry for not being clear on that.  

 

All the circuits at the destination are rcbo protected.  The source end has no RCD protection.

[ProDave]

1 hour ago, jpadie said:

On the destination end.  Sorry for not being clear on that.  

 

All the circuits at the destination are rcbo protected.  The source end has no RCD protection.

So the length of non armoured cable from the termination point to the remote CU will have to be located where RCD protection not needed, i.e. not buried in a wall.

[FuerteStu]

In answer it your first sentence.. 

 

No it isn't normal, or preferred, as it brings with it more complications and additionally work. 

 

Cable routing and sub-Mains board placement is done to avoid things like this. 

 

The only time I do this is when space is tight and you're glanding off into metal conduit or trucking all the way to the terminations (commercial or industrial situations) 

 

In domestic situations, that containment usually takes up more room than any bend radius. 

[Mattg4321]

SWA glanded and stripped back to the internal bedding (it’s not insulation or sheathing) is not suitable to be run outside of containment. 

[jpadie]

Thanks all.  

I'm having to run bigger SWA after the walls have been closed.  And I can't reuse the original cable routing as the service void is 20mm.  

 

The consumer unit is in a small cupboard and I need the whole width to be able to access and install a water tank.  Putting a 22mm cable there will impede access to the point of making it impossible 

 

So the only route left I think is to go up the outside of the building behind the consumer unit (behind the cladding) and penetrate the wall (tyvek, osb, 150mm PIR and plasterboard) at a steep angle and enter the interior at about 5ft then gland into the bottom of the consumer unit.  That will be high enough to allow access.  

 

Does the cable need to be derated materially for the short run in PIR?  The remainder will be buried.  

[Mattg4321]

A distance of 150mm through pir is not going to have a big impact on the current carrying capacity.