Need to earth back boxes? Earth sleeves etc.

[Draughtsman]

The 2 cables exiting between the bricks? Are they ok, 75mm below top of floorboard?

What clearance between pipes and cables is desirable?

I have the 'mock tudor' type ceilings, with the plasterboard recessed in halfway up the joists. That hole taking the cables out towards the bricks is on top of the batten. There isn't much space.

 

[mattylad]

The electricians will let you know about the brick clearance, however it was advised further up.
How much clearance from the pipes? enough to prevent the heat from the pipes affecting the cable, there will likely be a reg on it but I'd say 1/2"+ as that seems to be all you got perhaps some heat insulation between them would be better?

 

[scousespark]

Come now, you run a cable from one socket to the other, it's not rocket science. The fear mongering is tiresome. We all know how easy it is, if a spark gets offended because I can do their job, why come to a diy forum at all, just to slag off home diyers? Makes no sense, unless of course there are sparks here trying to pick up work with their constant put downs, and ''I'm better than you'' mentality.

Anyway, hiring someone from derry to do electrical work is a risk in itself

Installing falls between design and test and it’s the easy bit. The scare mongering is intended to help stop those with no knowledge getting it wrong.

 

[JohnW2]

How much clearance from the pipes? enough to prevent the heat from the pipes affecting the cable, there will likely be a reg on it but I'd say 1/2"+ as that seems to be all you got perhaps some heat insulation between them would be better?

As far as I am aware, there is no explicit regulation relating to clearances - which makes sense since no two situations will be identical.

"In contact" is clearly not desirable (but not all that uncommon) - but, even then, the cable is unlikely to actually be damaged. Don't forget that it will be 'rated' for a conductor temperature of 70° C, so undoubtedly could tolerate a fair bit more than that. However, what ambient temperature does affect is the current-carrying capacity of the cable.

Insulation between pipe and cable could be a mixed blessing. It would slow down the heating of the cable but, if the pipe were fairly constantly hot, the ultimate temp of the cable might not be much different - and might even be increased if the effect of the insulation was to restrict air flow around the cable.

For what it's worth, in my house there are cables that have been pretty close to hot water pipes for decades, and they don't seem to have come to any harm.

Kind Regards, John

 

[scousespark]

Indeed. It's inevitable that the case of an appliance with an L-E will be higher (probably much higher) than, say, the case of another appliance which has a separate CPC route back to the MET (or, as you go on to say, some other earthed object, like a sink). That is probably a good reason for not having Class I appliances in close proximity served by different circuits since, if they are on the same circuit, sharing the same CPC back to the MET, they are going to remain at essentially the same potentials. That's one reason why I'm not keen on two or more 20A radials supplying sockets in one kitchen.
Kind Regards, John

I may be a bit dim, but I’m not getting this. In the case of multiple radials for sockets, I can’t see where the extra cpc fits into picture.

 

[JohnW2]

I may be a bit dim, but I’m not getting this. In the case of multiple radials for sockets, I can’t see where the extra cpc fits into picture.

I'm not sure what you mean by 'the extra CPC'. As I see it ...

Each circuit has it's own CPC back to the MET and, in the absence of any of 'incidental' parallel paths to earth, that's the only earth connection which that circuit has. Again in the absence of incidental paths (and that could include local 'supplementary bonding'), there are no 'cross-connections' between CPCs of different circuits, other than at the MET.

If an appliance on one circuit develops a fault between line and an exposed-c-p (hence the circuit's CPC), then the potential (relative to the MET) of that exposed-c-p will rise (until a protective device hopefully operates), due to the current flowing in the circuit's CPC. In the meantime, if there is a nearby appliance on a different circuit, the exposed-c-ps of that will remain at MET potential (since there is no current flowing in that CPC, hence no voltage drop). There will therefore be a pd between the exposed-c-ps of those two nearby appliances.

That pd between the exposed-c-ps of nearby appliances would have been minimal had both appliances been on the same circuit (hence with the same CPC) or if local supplementary bonding were in place.

Is my reasoning incorrect (it wouldn't be the first time!) ?

Kind Regards, John

 

[Iggifer]

"In contact" is clearly not desirable (but not all that uncommon) - but, even then, the cable is unlikely to actually be damaged. Don't forget that it will be 'rated' for a conductor temperature of 70° C, so undoubtedly could tolerate a fair bit more than that

I tend to agree with you on the whole here, however we had to rewire a lighting circuit over the summer due to a N-E short. During that, I found - what I suspect was causing the fault.

A piece of T+E had been looped over a CH pipe and where the cable was in contact it had worked it’s way down to copper to short N to the earthed heating pipe.

Whether it had melted down to copper or it had rubbed with the movement of the pipe I don’t know, think it’s the one and only time I’ve seen that much damage from a pipe

 

[JohnW2]

A piece of T+E had been looped over a CH pipe and where the cable was in contact it had worked it’s way down to copper to short N to the earthed heating pipe. ... Whether it had melted down to copper or it had rubbed with the movement of the pipe I don’t know, think it’s the one and only time I’ve seen that much damage from a pipe

Interesting. We certainly inherited some cables here which had been literally 'wrapped around' CH pipes for very many years, and none seem to have suffered appreciably as a result.

Kind Regards, John

 

[Iggifer]

Interesting. We certainly inherited some cables here which had been literally 'wrapped around' CH pipes for very many years, and none seem to have suffered appreciably as a result.

Kind Regards, John

That’s my general experience too. I’ve seen many more undamged than damaged. This might have just been a low quality piece of T+E/particularly hot pipe

 

[mattylad]

Whilst you may have seen many that are undamaged through being in contact with CH pipes, I'm sure that you would agree that it is best practice to NOT be in contact with metal pipes that can get very hot.
Just like there are many other things that are best practice, or parts of regulations - they are there for a reason even though there is often no problem.

 

[JohnW2]

Whilst you may have seen many that are undamaged through being in contact with CH pipes, I'm sure that you would agree that it is best practice to NOT be in contact with metal pipes that can get very hot.

Of course. In fact, any pipes (or other things) which can get very hot, whether metal or not.

Just like there are many other things that are best practice, or parts of regulations - they are there for a reason even though there is often no problem.

Whilst it is literally true that all 'good practices' and regs are there 'for a reason' (because a group of people thought they were a good idea), I don't think one can assume that they are always there for reasons that are generally accepted as 'necessary' or 'reasonable', except in the eyes of extremely risk averse people. They nearly always exist to address some theoretical (and often extremely small) 'safety' risk, but in some cases there is a widespread belief that the cost (in the widest sense) is not really justified by the level and/or severity of the risk. Two current examples might be regulatory requirements for 'non-combustible' CUs and the (probably) upcoming requirement for all installations to have local earth electrodes.

It is also worth remembering that the 'good reasons' for introducing a regulation sometimes are deemed to have magically gone away (which begs the question as to how 'good' those reasons were in the first place) - such as most of the previous requirements for supplementary bonding, and also that regulations sometimes appear to be simply 'plain wrong' (like the apparent requirement to apply main bonding to things which are not extraneous-c-ps).

Back to the specific, as far as I am aware the regs say nothing specific about the proximity of cables to heat sources, and therefore essentially leave it to a designer's discretion, judgement and common sense, to satisfy the vague requirement for cables to be protected from thermal damage. Whilst I imagine that virtually no-one would regard it as good practice to have cables in contact with potentially very hot pipes (metal or not), but would also imagine that many/most would probably be happy with almost any 'sensible' degree of physical separation.

Kind Regards, John