Electrical cabling & CH pipework

[NearlyDIY]

I don't know if this is the right place, because my problem covers both electrics and plumbing!

We had a complete re-wire, everything fine. We then had to have the CH pipework replaced with copper pipes, as the old plastic was just that...OLD!

I've lifted some floorboards to check on some issues, and I've found that the plumber has put at least one of the pieces of piping below the electrical cable. When the floorboard goes back down, it appears to press the cable against the pipe, which gets hot. I'm concerned about the hot pipe damaging the cable and causing a potential fire hazard.

Am I right to worry?

 

[AndyPRK]

It's far from ideal and will certainly shorten the life of the cable.
I would want it correcting but I wouldn't say it's a fire hazard.

 

[PrenticeBoyofDerry]

I have come across many occasions where damage has occurred to the sheath and insulation of electrical cable due to contact with central heating pipework. I would suggest you call the plumber back and request them to correct the potential hazard they may have introduced.

 

[JohnW2]

I have come across many occasions where damage has occurred to the sheath and insulation of electrical cable due to contact with central heating pipework.

As a matter of interest, have you come across (m)any situations in which this has actually resulted in 'a problem' - i.e. are you just talking about 'visible/feelable damage', or have their been situations in which a problem has arisen as a result, or been detectable by testing (i.e. reduced IR)?

I would suggest you call the plumber back and request them to correct the potential hazard they may have introduced.

... and maybe also an electrician. It certainly isn't an ideal situation, and it also sounds as if the cable may be too close (quite possibly without adequate protection) to the floorboards.

Kind Regards, John

 

[ericmark]

I would also say although since central heating can be 70 degrees and cable maximum temperature is also 70 degrees this is far from ideal and needs correction.

However as to real fire risk who knows? If there is a fire then yes may work out caused by faulty cable but once the fire has happened could one still see how close the pipe work was? So as to reports of fires caused by cables and central heating pipes being too close it's unlikely there will be any.

Where the cable feeds the central heating boiler the cable is so big for current it carries unlikely ever to be a problem it's power cables to other things which are likely to suffer.

I have removed one cable in my mothers house spur from spur from spur where an electric fire often used which had failed but this is unusual I can't remember any other twin and earth plastic cable where the cable failed a IR test so I think the cases where central heating and electric cables cause a problem are very few but still wants correcting.

I have found many times where other trades have tried to use holes I have drilled or tray work I have erected for electric cables. Not only Plumbers also alarm people have done the same mixing ELV with LV cables.

 

[JohnW2]

I would also say although since central heating can be 70 degrees and cable maximum temperature is also 70 degrees this is far from ideal and needs correction.

Indeed,as we've both said, far from ideal - but, as you imply, not actually as 'dramatic' a situation as one might at first think. The usual PVC cables are 'rated' for continuous use at a conductor temperature of 70°C, and even the flow pipe of a correctly adjusted CH system should not usually be above that. However, as you go on to imply, the potential problem arises if a cable already in contact with a 70°C pipe is also heavily loaded (electrically), so that the temperature could rise to appreciably above 70°C - although,in practice, such a situation is probably unlikely to arise for appreciable periods of time (coupled with the fact that one side of the T+E should remain able to dissipate heat into the environment).

A number of years ago, I removed a length of (in-service) imperial PVC T+E which, for goodness knows how many years (and goodness knows for what reason!), had literally been 'wound around' a CH pipe for a substantial distance - and the cable seemed to have come to no great harm.

Kind Regards, John

 

[PrenticeBoyofDerry]

As a matter of interest, have you come across (m)any situations in which this has actually resulted in 'a problem' - i.e. are you just talking about 'visible/feelable damage', or have their been situations in which a problem has arisen as a result, or been detectable by testing (i.e. reduced IR)?

On one occasion I came across a situation where the outer grey sheath of a 3C&E has completely melted, which also resulted in damage to cable insulation of the cores within, where a live conductor was exposed. There has been others where the sheath has been damaged and the insulation become brittle. This has normally come visually apparent whilst doing other electrical work within the void, rather than detection/investigation via measurement through testing.

 

[JohnW2]

On one occasion I came across a situation where the outer grey sheath of a 3C&E has completely melted, which also resulted in damage to cable insulation of the cores within, where a live conductor was exposed. There has been others where the sheath has been damaged and the insulation become brittle. This has normally come visually apparent whilst doing other electrical work within the void, rather than detection/investigation via measurement through testing.

Thanks, that's interesting. IIRC the melting point of standard PVC is around 150°C, so I presume that it must have been a pretty highly loaded (electrically) cable which melted.

Kind Regards, John

 

[NearlyDIY]

Many thanks to all for replies.

The cabling looks as though it's been inserted fine. There's a gouge has been cut out of the joist for the cables, I think there's about 5 in all, and they all fit into the gouge OK. The problem appears to be from a pipe going to a radiator. It looks as though a separate gouge has been cut into the joist for the CH pipe. From this, there's a pipe been taken for the radiator. However rather than putting the pipe over the cable, and there appears to be plenty of room for it, the plumber's done it the other way…cable over pipe. This has resulted in the pipe coming into contact with the cabling, which is lifting the cabling up causing it to be pressed against the floorboard.

From what has been said, the plumber needs replace the pipe putting it above the cables to reduce any chance of damage to them.

Cheers all for your help.

Duncs

 

[JohnW2]

...There's a gouge has been cut out of the joist for the cables, I think there's about 5 in all, and they all fit into the gouge OK. The problem appears to be from a pipe going to a radiator. It looks as though a separate gouge has been cut into the joist for the CH pipe. From this, there's a pipe been taken for the radiator. However rather than putting the pipe over the cable, and there appears to be plenty of room for it, the plumber's done it the other way…cable over pipe. This has resulted in the pipe coming into contact with the cabling, which is lifting the cabling up causing it to be pressed against the floorboard.

Can you explain what you mean by 'gouges' and exactly where they are in the joist?

Kind Regards, John.

 

[NearlyDIY]

[/quote]
Can you explain what you mean by 'gouges' and exactly where they are in the joist?
[/quote]

Probably not the best of ways to describe it!

On the top of the joists, there were holes cut out from where the previous wiring / CH piping had ran.

The electrician has used these to run the cable. There have also been some joists, especially in the hall where I have this issue, where the joist has two cut-outs...one for the CH pipe(s) and one for the cabling.

So, from the side, the joist looks as follows...figures are not representative, just makes it easier to describe. I couldn't get a drawing is, so have to resort to text description.

There's a 3" section of wood on the surface of the joist. There's then a 2" section of the joist that's been cut out, to a depth of 1". This carries two CH pipes. There's a 3" section of wood, on the surface of the joist. Then, it's a 3" x 1.5" cut-out of the joist. This carries the cables. Finally, it's a 3" section of wood on the joist surface.

Not far behind that joist, there is a lead off for a CH rad. However there is wiring that has to come through. What the plumber has done is:

Taken a feed from the pipe on the left and dipped it slightly behind the cabling feed on the right. He's then put the pipe under the cables, which has forced them up to be resting on the pipe. It has also meant the cables are sitting higher that they would / should normally be, causing them to press aganst the floorboard which, I'm sure, is causing them to press harder against the CH pipe.

Have I explained it better...or just muddied the waters?

 

[sparkwright]

We call it a notch.

Where there is section of the top of the joist cut out.

Where electricians use notches, a metal nail guard needs fitting at the top of the joist to prevent nail penetration.

Only lazy electricians usually use notches. The best way is to drill holes through the joists, done at a depth to prevent nail penetration from above and below.

It's best to keep wiring away from pipework, and is nearly always possible.

Leave the notches to the plumbers.

PS
Anyone experienced after you have drilled joists and run your cables, some plumber comes along and notches immediately above your cables, and then run pipes?

Bloody annoying, especially if you want to install another cable. Not to mention the other problems.

 

[JohnW2]

... There's a 3" section of wood on the surface of the joist. There's then a 2" section of the joist that's been cut out, to a depth of 1". This carries two CH pipes. There's a 3" section of wood, on the surface of the joist. Then, it's a 3" x 1.5" cut-out of the joist. This carries the cables. Finally, it's a 3" section of wood on the joist surface.

Fair enough. So there's one notch (which you now know is the word!) for cables and the other for pipes. That's common enough - although if there is no metal protection above the cables, that would not be compliant with current regulations (but you're under no obligation to update to current regs).

Not far behind that joist, there is a lead off for a CH rad. However there is wiring that has to come through. What the plumber has done is: ... Taken a feed from the pipe on the left and dipped it slightly behind the cabling feed on the right. He's then put the pipe under the cables, which has forced them up to be resting on the pipe.

Are you saying that the plumber has put this new pipe in the 'cables' notch?

Kind Regards, John

 

[PrenticeBoyofDerry]

On the top of the joists, there were holes cut out from where the previous wiring / CH piping had ran.

The electrician has used these to run the cable. There have also been some joists, especially in the hall where I have this issue, where the joist has two cut-outs...one for the CH pipe(s) and one for the cabling.

These are known as notches and the cable should be mechanically protected when routed in theses. A safe plate should have been fitted across the notch. There are also building regulations on where and what depth these can be.
//www.diynot.com/wiki/Electrics:route

Not far behind that joist, there is a lead off for a CH rad. However there is wiring that has to come through. What the plumber has done is:

Taken a feed from the pipe on the left and dipped it slightly behind the cabling feed on the right. He's then put the pipe under the cables, which has forced them up to be resting on the pipe. It has also meant the cables are sitting higher that they would / should normally be, causing them to press aganst the floorboard which, I'm sure, is causing them to press harder against the CH pipe.

To me it sounds like both electrician and plumber need to come back and re-address their work.

Have I explained it better...or just muddied the waters?

Explanation was fine.

 

[NearlyDIY]

Are you saying that the plumber has put this new pipe in the 'cables' notch?
[/quote]

No, the plumber has put a pipe behind the joist running from the CH pipe into the radiator, and parallel to the joist. The cables then cross over the pipe.