Hot water pipes and cable runs.

Spook · 18 Jan 2010

Sorry if this has already been addressed elsewhere.

In the process of replacing a couple of floors in my new place I've noticed that in some places cables supplying both the lighting and ring circuits pass very close to hot-water pipes.

I understand that this must be fairly common where cable and pipe runs have been done at different times, and even in ideal circumstances it must sometimes be unavoidable - but I have a couple of questions:

Does the heat coming from a hot-water pipe have any potential detrimental effect on a cable? Is there a minimum recommended distance between a cable and a pipe carrying hot water? Should cables be shielded in some way if they do pass close to a pipe?

My mistake - that's three questions, isn't it?

Thanks for your time.

Spook.

timtheenchanter · 18 Jan 2010

dont know about hot water, but CH pipes can melt T&E, had it happen at my house (some numpty added a spur, ran cables in same joist notch as CH pipes.

I have now had to re-route these, luckily I found it BEFORE it cased an issue, I have seen holes blown in pipes from a cable-water pipe short.

rebuke · 18 Jan 2010

Indeed - while putting in some data cabling I discovered a bit of T&E sitting on top of one of the flow/return pipes to the boiler, with the insulation starting to blacken - I suspect the previous owner did it when he re-did the kitchen...

papyrus · 18 Jan 2010

I have just had the same issue. The central heating pipes run along the wall under the first floorboard. I would like to run cables to three sockets on the same wall. I need to either

- put the cables along the pipes
- drill holes in the joists near the notches for the pipes (would not do this)
- pick up another board nearer the middle of the room and put the cables under it (not keen as the floor is in really good condition and will be stripped.

The standard cables are rated to 70°C (BS6004). This should be enough to withstand most central heating pipes (though some run at up to 80°C). Hm? Or is there a way to insulate the cables or the pipes where they are near?

JohnD · 18 Jan 2010

the heat shortens the life of the PVC insulation a lot, as well as the softening effect which (if a board for example is pressing the cable and pipe together, can cause the copper to migrate through)

however, if you put Climaflex or other pipe insulation to keep the cable from touching the pipe, this will help a lot.

Putting the cables through holes drilled in the midpoint of the joists is the best place.

Here's one I found earlier:

View media item 1632
View media item 1631
(the green slime is quite rare)

ColJack · 18 Jan 2010

simply outstanding junction box there...

JohnD · 18 Jan 2010

I went back later with my Crimpers

skenk · 18 Jan 2010

papyrus said:
I have just had the same issue. The central heating pipes run along the wall under the first floorboard. I would like to run cables to three sockets on the same wall. I need to either

- put the cables along the pipes
- drill holes in the joists near the notches for the pipes (would not do this)
- pick up another board nearer the middle of the room and put the cables under it (not keen as the floor is in really good condition and will be stripped.

The standard cables are rated to 70°C (BS6004). This should be enough to withstand most central heating pipes (though some run at up to 80°C). Hm? Or is there a way to insulate the cables or the pipes where they are near?

You shouldn't be notching or holing joists in the centre of the span or next to the wall (within 0.04 of the end of the span)

papyrus · 18 Jan 2010

You shouldn't be notching or holing joists in the centre of the span or next to the wall (within 0.04 of the end of the span)

I know. I did not make those notches next to the wall, but the central heating installers of the seventies did. This is why I don't want to put more notches or holes nearby. But then where should the cables go? I am leaning towards the solution of insulating the pipes and putting the cables alongside.

(this room had essentially no wiring, apart from a surface-mounted socket on each side of the door)

Taylortwocities · 18 Jan 2010

Do not do this at home (or anywhere!)

Untitled

Taylortwocities
12 Oct 2008
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Spook · 19 Jan 2010

Thanks all.

In my own situation there is only one shortish run where cable is sharing the same notches as the pipes and I'd already decided to get that replaced and rerouted that when I next get an electrician in.

From what I can see the problem is generally not one of cables and pipes actually touching - just running, in places, within a couple of inches or so of each other. In this situation would it still be advisable to insulate the pipe from the cable, or is it not an issue unless the two are actually touching? Goes back to my original question as to whether there's a minimum recommended distance between cable and pipes carrying hot water - given the amount of regs and recommendations out there, I'm surprised I can't find one.

Yeah, okay. I know I'm probably being anal. Again. But the magic string always makes me a little nervous.

Cheers.

Spook.

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Hot water pipes and cable runs.

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