Pipes - Electric Cables

[hoyboy]

Hi,

Are there any regulations on how close to central heating pipes and boilder electric cables can go? I'm just installing a kitchen and trying to chase ready for the electrican. If I can run cable loose around the boiler and down the boxed out section holding the water pipes it's going to massively reduce the amount of chasing I have to do but wondered if they had to all be kept seperate?

James

 

[GaryMo]

I'm not aware of a distance though there may well be one (would love to know if there is) but you have to apply common sense.
Don't run cables near hot water or heating pipes etc as this will have a direct effect on the cable with regards to its current carrying capacity. It will also reduce the lifespan of the cable.
Go the extra mile and chase the cables into a safe wiring zone.

Maybe you should be asking the electrician who's going to certify and Part P this work.

 

[JohnD]

if the cable is loose it is very liable to flop onto hot pipes etc and will be softened. In some cases this causes the conductors to grin through and possibly contact a pipe.

If you thread it into oval conduit, you can then clip the conduit to the wall using 16mm clips, and it is rigid enough to stay where you want it and look neat and tidy, and easy to poke through gaps. As it is surface mounted it is less prone to nail and drill damage.

Yes, heat will shorten the life of PVC insulation. Run the cables (in conduit) below the boiler and insulate any nearby pipes.

 

[gas4you]

When doing Part P we were told it was 50mm I think, gas pipes are definately 25mm miniumum, can't remember CH pipes exactly though

 

[Chivers7]

Put some insulation round the pipes just to save energy

 

[stargazer]

I found some 1.5 twin and earth wrapped around my central heating feed pipe when lifting the floorboards in our bedroom. Wrapped tight like a snake around its prey.
The plumbers who installed our central heating 18 years ago must have unknowingly done it when threading the pipes under the floor.
Here's the thing though - no obvious signs of damage at all
NOT to be recommended though

 

[daytona]

if the pipes raise the ambient temperature of the cable,wouldnt that be classed as an external influence?

 

[Spark123]

When doing Part P we were told it was 50mm I think, gas pipes are definately 25mm miniumum, can't remember CH pipes exactly though

Even if they are mounted 50mm away, in a boxed section with C/H pipes the ambient temp can be a problem. Best way is to try your best to keep the cable away from this type of setup.

 

[hoyboy]

Thanks - is it definately 50mm from CH pipes and 25mm from gas? Just had a better look round the kitchen and all cables are closer than that. Basically, they're just cable tied to the wall and left to hang down ontop of the pipes. Gas pipes are bare but CH are insulated and all are under cabinets with a big air space so temperature shouldn't be a big problem - just worried about the law?!

Think the CH was put in after the spark did his stuff and the plumber may not have been aware of the law?

Also, I want to re-route a few cables and do need them to cross over pipes closely so was wondering how I can do this?

 

[JohnD]

climaflex pipe insulation (or similar stiff plastic foam) is very effective, it will hold the cables away from the pipes and also prevent the escape of much heat.

If you have room for it, the "BS" grade of pipe insulation is remarkably thick and effective. If you insulate the whole of theg piupe it will keep the ocal ambient temperature down as well. It is available at any DIY or plumbing shop, in sizes for 15mm and 22mm pipes. 28mm is probably not in the DIY shed..

I recently came across some PVC T&E in contact with domestic boiler pipes, and it had gone stiff, scaly and dripping green slime

It had been in for more than 30 years, though.

 

[jason1958]

1. Lag the pipe or increase cable CSA to compensate.

Cable is derated based upon installation factors.
- Installation method (M1, M3, M6, etc)
- Ambient temperature
- Cable grouping
- Rewireable fuses
- Insulation completely surrounding the cable

Taking 6242Y (FTE)...
- 30oC = 1.00 derating - ie, none
- 45oC = 0.79 derating
- 55oC = 0.61 derating
- 60oC = 0.50 derating

Say your cable is part of a ring final circuit.
- Minimum current capacity per leg is 20A after ALL derating factors
- 2.5mm FTE has uncorrected figure of 27A
---- You run 1 leg near to a heat source at 60oC
---- You apply a 0.50 derating to 27A, creating 13.5A - far below 20A
---- You *must* reduce ambient (lag pipe) or increase cable size
- 4.0mm FTE has uncorrected figure of 37A
---- You run 1 leg near to a heat source of 60oC
---- You apply a 0.50 derating to 37A, creating 18.5A - still below 20A

So you can see how it is cheaper to lag the pipes


2. Gas pipe vs Cable/Skt/Switch separation by Gas Regs BS6891-2005

BS6891-2005
8.16.2 Separation of installation pipework from other services

Where installation pipes are not separated by electrical insulating material, they shall be spaced as follows: a) at least 150 mm away from
electricity meters and associated excess current controls, electrical
switches or sockets, distribution boards or consumer units;
b) at least 25mm away from electricity supply and distribution cables.

Electrical insulating material is not really meant to mean a piece of paper or heatshrink over cable, just use common sense and a simple piece of rigid or flexible conduit as necessary (and check installation method if a long run).


So as always, avoid cooking your cable particularly if a ring.
- Rings can suffer breaks
- Rings can suffer imbalance as usage changes or temporary changes

If the cable is already being "cooked", those events can push it over the edge with insulation suffering, bad IR results at a PIR or failure.
Nothing worse than having to rip out kitchen tiles, trying to miss numerous Gas HW CW pipes, in order to replace a leg.

So apply common sense, lagging is cheaper than copper

 

[hoyboy]

Thanks - I'll insulate the pipe and put the cable in flexible conduit then... just to make sure.

 

[industryspark]

gas4you wrote:

gas pipes are definately 25mm miniumum

Where can i see information for this? Id be interested. Where i work there are some armoured cables running within this distance of gas pipes for some distance. I once picked the brain of a gas installer who was doing some work for the company and he said he wasnt aware of any regulation against this setup either so havent really given it any thought since.

BS7671 doesnt give a direct recommendation on this scenario and to be honest in a lot of industrial installations i cant imagine how this would be fully achieved anyway.