Terminating Outside circuits with SWA

[Roger440]

Thanks for the pics.

 

Follow the logic on heatshrink on the single conductors. Hadn't thought of that. Like yours its all "inside" the cupboard with electrics in.

[Jeremy Harris]

As far as the regs go, being inside a box or cupboard is treated the same as being exposed, if the box or cupboard can be opened without the use of tools (and a meter box key doesn't count as a tool in this case).  The principle is to ensure that there are two layers of insulation over any line or neutral conductor that is in a location where it could be poked with a small finger, in essence.

 

I used heavy duty grey heatshrink sleeving to insulated the single insulated conductors, effectively making them identical to standard meter tails.  The only thing to watch is to use a low temperature non-adhesive heatshrink, as the insulation on the cores will probably be PVC, that won't tolerate the high temperature stuff.

[ProDave]

Can I ask the obvious question.

 

Why do you want to terminate them outside?

 

The logical and normal thing is bring the SWA cables inside, whole, and terminate them directly into the consumer unit with the correct glands. 

[Roger440]

3 minutes ago, ProDave said:

Can I ask the obvious question.

 

Why do you want to terminate them outside?

 

The logical and normal thing is bring the SWA cables inside, whole, and terminate them directly into the consumer unit with the correct glands. 

Mainly because as they run up the wall, they will have to do a 90 degree turn which will look awful as they will stick out. It certainly a very visible area. Then of corse the same again inside. Currently its a plastic CU, though i guess i could change that.

 

Even if i came in closer to the floor, ive still got to turn a 16mm cable through 90 degrees.

 

I suppose could try going through at an angle, but its conventional brick and block with cavity. Still look crap though.

[Roger440]

30 minutes ago, JSHarris said:

As far as the regs go, being inside a box or cupboard is treated the same as being exposed, if the box or cupboard can be opened without the use of tools (and a meter box key doesn't count as a tool in this case).  The principle is to ensure that there are two layers of insulation over any line or neutral conductor that is in a location where it could be poked with a small finger, in essence.

 

I used heavy duty grey heatshrink sleeving to insulated the single insulated conductors, effectively making them identical to standard meter tails.  The only thing to watch is to use a low temperature non-adhesive heatshrink, as the insulation on the cores will probably be PVC, that won't tolerate the high temperature stuff.

 

By that would i be correct in assumimng inside the CU it would no longer be necessary?

 

[Ed Davies]

Am I right in thinking that the logic of requiring double insulation, rather than just an equivalent extra thickness of single insulation, is that any cracks or splits in one are unlikely to line up with any in the other or propagate through or is there more to it than that? That one will act as a strain relief for the other?

[Jeremy Harris]

8 hours ago, Roger440 said:

 

By that would i be correct in assumimng inside the CU it would no longer be necessary?

 

 

Yes, any conductor inside an enclosure that needs tools to open, like a CU box, only needs to be single insulated.

 

8 hours ago, Ed Davies said:

Am I right in thinking that the logic of requiring double insulation, rather than just an equivalent extra thickness of single insulation, is that any cracks or splits in one are unlikely to line up with any in the other or propagate through or is there more to it than that? That one will act as a strain relief for the other?

 

I believe that's the rationale behind needing two layers of insulation that aren't bonded to each other, but for the life of me can't find the relevant supporting evidence right now.  IIRC it goes right back to the very first introduction of Class II equipment, which then led on to using two layers, or a single, thicker, reinforced layer of insulation on cables.  This is about the time that the design of the BS1363 plug changed to include partially insulated L and N pins, IIRC.

 

Things like meter tails, for example, just had a single insulation layer years ago, not two as they have now.  The same went for cables used to supply incidental lights, or pendant drops, although these now have to use cable with either double insulation or thicker, reinforced, insulation.

[Nickfromwales]

8 hours ago, Ed Davies said:

Am I right in thinking that the logic of requiring double insulation, rather than just an equivalent extra thickness of single insulation, is that any cracks or splits in one are unlikely to line up with any in the other or propagate through or is there more to it than that? That one will act as a strain relief for the other?

The requirement is one layer of electrical insulation, and one layer or means of mechanical protection. The outer layer being sacrificial to the inner.  

[Nickfromwales]

Crossed with J.

As per my last, hence, you can put PVC singles in a minimal trunking or conduit and it is compliant.  

[Jeremy Harris]

Just in case anyone wonders about things like test leads etc that appear to have single insulation, then it's OK to have a single, thicker, reinforced layer of insulation for certain applications. 

 

Apart from test gear cables, the only other place you're likely to see single reinforced insulation in place of double insulation in a domestic setting are things like lighting circuits, where some types of, usually decorative, cable may be only single insulated, but have reinforced insulation that meets the regs for that application.  We have an art deco lamp that has what looks like old cotton-covered cable, but which is really brand new reinforced single insulated cable with a woven covering over the outside to look the part.