No CPC on one of my lighting circuits - worth amending?

[JohnW2]

Maybe, but you can't worry about everything.

Very true, but some people (and sometimes the regs) often try to

What are the current rules about cables in cavities?

A very good question. There seems to be a widespread belief that running cables in wall cavities is 'not allowed', but I can find nothing in BS 7671 that appears to say that. Is this perhaps yet another of those myths?

Kind Regards, John

 

[securespark]

You have to be careful about detrimental environments. If the cavity is stuffed with expanded poly, you need to shield the cable against contact, which in most cases is difficult or impossible.

 

[sparkwright]

Very true, but some people (and sometimes the regs) often try to

A very good question. There seems to be a widespread belief that running cables in wall cavities is 'not allowed', but I can find nothing in BS 7671 that appears to say that. Is this perhaps yet another of those myths?

Kind Regards, John

I can't quote any reg numbers, but I think there was one rule about cables in cavities being secured (with clip or clips).

 

[JohnW2]

I can't quote any reg numbers, but I think there was one rule about cables in cavities being secured (with clip or clips).

The nearest I could find was a reg saying that they had to be adequately supported to prevent them being damaged 'by their own weight', but I seriously doubt that would ever be a risk with the sort and length of cables we are talking about.

I can't find anything else specific - maybe someone else can?

Kind Regards, John

 

[sparkwright]

The nearest I could find was a reg saying that they had to be adequately supported to prevent them being damaged 'by their own weight', but I seriously doubt that would ever be a risk with the sort and length of cables we are talking about.

I can't find anything else specific - maybe someone else can?

Kind Regards, John

Yes, damaged by their own weight rings a bell.

I can't see vertical drops being much of a problem TBH.

Although a long horizontal run can get very heavy.

 

[sparkwright]

You have to be careful about detrimental environments. If the cavity is stuffed with expanded poly, you need to shield the cable against contact, which in most cases is difficult or impossible.

I suppose one could 'get away with it' if there was no poly in the cavity?

Though poor design.

Cavity insulation surveyors don't seem to take the detrimental effects of cables into account. You can tell them that cables are already in the cavities, and that they need to avoid using poly, they nod and say they will use wool, then they go and use poly.

I think the cavity insulation people need to take more responsibility in this area.

 

[JohnW2]

Yes, damaged by their own weight rings a bell. I can't see vertical drops being much of a problem TBH.

Indeed not.

Although a long horizontal run can get very heavy.

I wouldn't think that any credible length of horizontal run of ≤4mm² would be likely to be a problem, would it?

Kind Regards, John

 

[securespark]

.

.

 

[sparkwright]

I wouldn't think that any credible length of horizontal run of ≤4mm² would be likely to be a problem, would it?

Kind Regards, John

Gets surprisingly heavy after just a few metres, if anyone was thinking about stuffing something like 10m or so down a cavity horizontally - which unfortunately people do sometimes to save a bit of cable clipping - I suppose you risk stretching the cable.

 

[JohnW2]

Gets surprisingly heavy after just a few metres,

Maybe, but that's why I said 'credible' lengths. How many metres of horizontal cable run in a cavity do you think would be 'credible' in the average house?

Kind Regards, John

 

[mattylad]

That is one of the so called regs that don’t make sense. I would happily ignore it and use 1.0 mm green/yellow wire. Much safer than no earth and just as safe as T& E.

Well I never, Winston said something that we are agreeing with - wonders will never cease

I think whatever the reason for the reg saying 4mm should be used I think that a lesser size earth would be better than no earth.

 

[sparkwright]

Maybe, but that's why I said 'credible' lengths. How many metres of horizontal cable run in a cavity do you think would be 'credible' in the average house?

Kind Regards, John

I don't know.

Let's say someone wants a socket at the opposite end of the lounge diner - that could be 8 metres or so.

 

[JohnW2]

I don't know. Let's say someone wants a socket at the opposite end of the lounge diner - that could be 8 metres or so.

It's obviously possible to think up such scenarios, but I would think it pretty unlikely if someone would want a socket 8 metres from the nearest one without anything in between. In practice, in a 'typical house', I would have guessed that 3-4 metres would be the longest 'likely' horizontal run.

Kind Regards, John

 

[sparkwright]

It's obviously possible to think up such scenarios, but I would think it pretty unlikely if someone would want a socket 8 metres from the nearest one without anything in between. In practice, in a 'typical house', I would have guessed that 3-4 metres would be the longest 'likely' horizontal run.

Kind Regards, John

I would agree on 3-4 metres realistically.

Even then, I suppose the cable may be 'supported' by wall ties (ouch).

 

[JohnW2]

I would agree on 3-4 metres realistically. Even then, I suppose the cable may be 'supported' by wall ties (ouch).

There is perhaps another issue.

I personally very much doubt that T+E of any size would, per se, be damaged 'due to it's own weight', even if it were an 8m horizontal run. However, given that neither back boxes nor accessories have any 'strain relief', there could be an issue in relation to that if the weight of unsupported horizontal runs of cable were trying to pull the conductors out of their terminations.

Kind Regards, John