Foam and cabling

[ban-all-sheds]

You wouldn't think it would have been unnecessary if that 100mm section of cable had sustained damage due to overheating.

Whether the rest of the cable was 5m or 50m in length is irrelevant. No matter how small a percentage of it runs through insulation that section will heat up in just the same way.

 

[JohnW2]

You wouldn't think it would have been unnecessary if that 100mm section of cable had sustained damage due to overheating.

I wouldn't, if that happened. Nor, however, would I really expect it to happen.

Whether the rest of the cable was 5m or 50m in length is irrelevant. No matter how small a percentage of it runs through insulation that section will heat up in just the same way.

I obviously realise that, and didn't suggest otherwise. However, what I was saying is that if I wanted to address that issue, I probably wouldn't feel too inclined to run a whole 50m circuit in larger cable just because 0.2% of it's length needed to be larger - as I said, even though it would involve extra, quite possibly concealed, joints, I would probably be far more inclined to insert a very short bit of the larger cable where it went through the insulation.

Kind Regards, John

 

[EFLImpudence]

I would fill the hole with something else - cement?

 

[JohnW2]

I would fill the hole with something else - cement?

If it were a hole in a masonry wall, then so would I. However, there must be many cases in which a few inches of cable in a a circuit 'tens of metres long' (and nearly all Method C) unavoidably has to pas through insulation. If that bit in insulation had a strictly inadequate CCC (inadequate for the full design current of the circuit), I think I would then probably make a 'risk assessment', as to which presented the greater risk - that few inches of cable in insulation with a (probably only slightly) 'inadequate CCC' (and factoring in the fact that, for most circuits, it is extremely unlikely that any circuit would carry its full design current for a long period of time) or two additional, probably inaccessible, joints in the circuit.

Kind Regards, John

 

[EFLImpudence]

If it were a hole in a masonry wall, then so would I.

I thought that's what you were talking about.

However, there must be many cases in which a few inches of cable in a a circuit 'tens of metres long' (and nearly all Method C) unavoidably has to pas through insulation.

As BAS has said, it is irrelevant how long it is.
Does a cable not get burned by a blowtorch if it is long enough?

If that bit in insulation had a strictly inadequate CCC (inadequate for the full design current of the circuit), I think I would then probably make a 'risk assessment', as to which presented the greater risk - that few inches of cable in insulation with a (probably only slightly) 'inadequate CCC' (and factoring in the fact that, for most circuits, it is extremely unlikely that any circuit would carry its full design current for a long period of time) or two additional, probably inaccessible, joints in the circuit.

I cannot see a situation where it is unavoidable to run through insulation for a few inches.
Remove some insulation or if that is forbidden then the cable should not be there.

 

[JohnW2]

If it were a hole in a masonry wall, then so would I.

I thought that's what you were talking about.

No, BAS was. As I said, I was thinking about just sealing around holes in panels, enclosures etc.

However, there must be many cases in which a few inches of cable in a a circuit 'tens of metres long' (and nearly all Method C) unavoidably has to pas through insulation.

As BAS has said, it is irrelevant how long it is. Does a cable not get burned by a blowtorch if it is long enough?

And, as I responded to BAS, I obviously understand that. I've never suggested that being only a small proportion of the total length has any bearing on the heating of the bit of cable in insulation. What I have been suggesting is that, if I were concerned about the few inches in insulation, I'd be more inclined to buy 49.5m of 2.5mm² cable and 0.5m of 4mm² than having to buy 50m of 4mm².

If that bit in insulation had a strictly inadequate CCC (inadequate for the full design current of the circuit), I think I would then probably make a 'risk assessment', as to which presented the greater risk - that few inches of cable in insulation with a (probably only slightly) 'inadequate CCC' (and factoring in the fact that, for most circuits, it is extremely unlikely that any circuit would carry its full design current for a long period of time) or two additional, probably inaccessible, joints in the circuit.

I cannot see a situation where it is unavoidable to run through insulation for a few inches. Remove some insulation or if that is forbidden then the cable should not be there.

I suppose that might often be possible. However, I'd be very surprised if there also aren't countless circuits out there which, although regarded (and designed, CCC/CSA-wise) as 'clipped direct', have a few inches in insulation somewhere!

If/when the situation does arise, I think I've given enough hints as to what my 'risk assessment' would probably conclude (in the case of a small number of inches of cable in insulation) - particularly since, as I said, it must be pretty unusual to have a situation in which one considers it 'likely' that a circuit would have to carry its full design current 'for a long period'.

Kind Regards, John

 

[Taylortwocities]

Well, here we all are again.

The "BIGBRAINS" of DIYnot.com/electricians have dived in with their mouthing off.

And (yet again) a DIYer has asked a simple question and has been scared off because the BIGBRAIN egos have taken over with points scoring over other BIGBRAINS.

Do any of your egos have an idea how can we fix this rather boring way of spending our spare time

 

[JohnW2]

Well, here we all are again. ... The "BIGBRAINS" of DIYnot.com/electricians have dived in with their mouthing off. ... And (yet again) a DIYer has asked a simple question and has been scared off because the BIGBRAIN egos have taken over with points scoring over other BIGBRAINS.

Well, I for one, did attempt to address the OP's simple question (as I saw it), after you and others had commented on CCC (perhaps slightly 'cryptically', as skotl commented, and tried to clarify) ....

Aah yes. I wonder what the Stuntman is planning…….

We currently can but guess! It's quite probable that the only question he thought he was asking was whether expanding foam damages PVC cable (and the answer is that polyurethane expanding foam is fine in contact with PVC cables) - but, as all the answers so far have indicated, he will then have discovered that there are other questions that he should have been asking! ...

However, I obviously made a mistake by adding ...

... We are most often asked this question in relation to just 'sealing around' a cable where it goes through some hole, and I am personally inclined to say that one should not worry about possible CCC issues in that situation.

...whereupon BAS 'took me to task', and (as usual) everything else followed!!

Kind Regards, John

 

[Johnmelad]

whereupon BAS 'took me to task', and (as usual) everything else followed!!

Time he was shown the door.

 

[ban-all-sheds]

However, I obviously made a mistake by adding ...

... We are most often asked this question in relation to just 'sealing around' a cable where it goes through some hole, and I am personally inclined to say that one should not worry about possible CCC issues in that situation.

...whereupon BAS 'took me to task', and (as usual) everything else followed!!

I "took you to task", if that's how you want to term it, because you were wrong, and the advice which you gave could be dangerous.

I agree wholeheartedly that if a cable runs through insulation for a short distance it may be much more appropriate to just have that short section increased in size than the whole length. But that is not "not worrying" about CCC issues, it is quite the opposite - it is recognising that the "possible CCC issues" cannot be ignored.

 

[Unknownstuntman01]

Hi, thank you for your replies, I will try to digest and sorry for opening a can of worms!

I only had a small penetration through an internal wall and I was wondering if by using the foam it would degrade the cables in any way.

 

[JohnW2]

Hi, thank you for your replies, I will try to digest and sorry for opening a can of worms! ... I only had a small penetration through an internal wall and I was wondering if by using the foam it would degrade the cables in any way.

As I said very early on, expanding polyurethane foam will not harm PVC cables.

As you will have seen, the subsequent 'can of worms' all relates to the possible overheating of cable when it is surrounded by insulation. As I've said, I personally really don't think it's an issue if you are just 'sealing around' where the cable enters a hole in a wall, but if you would like a definitive, hopefully 'reassuring', answer, you would need to tell us (a) the size of the cable, (b) the rating of the fuse or MCB in your CU which is serving the circuit concerned, (c) the nature of the circuit concerned (e.g. 'sockets ring circuit') and the approximate length of cable that would be encased in the foam.

Kind Regards, John