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Cable to water pipe separation

Postby ceri1 » Sun May 11, 2008 2:06 pm

We have pipes (including hot water) running along a wall, with electric cables just below. Electrician said we must separate them. 16 ed on-site guide says "cables should not bi in contact with, or run alongside hot water pipes. Installation must comply with bs7671, chapter 52+54, regarding separation and bonding", which isn't helpful.
Can anyone tell me what gap i need between the water pipes and the electrica cables and whether this gap could be reduced by putting the cables inside ducting?
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Postby ericmark » Sun May 11, 2008 6:09 pm

In the 17th Edition there are two references to proximity to water pipes. In both cases it is the heat produced that is the problem. The exact solution you need to work out this could of course include the use of cables more able to stand the heat the heat of the cables would need measuring and reference to table 4B1 will show the de-rating factor to be used. The max temp for standard twin and earth is 60°C but low smoke cable could run at 80°C but at those temperatures cable sizes would need to be double that used at the standard 30°C. I don’t have an old 16th Edition to hand but I would not think there has been any great change.
522.2.1 In order to avoid the effects of heat from external sources, one or more of the following methods or an equally effective method shall be used to protect it wiring system:
(i) Shielding
(ii) Placing sufficiently far from the source of heat
(iii) Selecting a system with due regard for the additional temperature rise which may occur
(iv) Local reinforcement or substitution of insulating material.
528.3.1 A wiring system shall not he installed in the vicinity of services which produce heat, smoke or fumes likely to be detrimental to the wiring. unless it is protected front harmful effects by shielding arranged so as not to affect the dissipation of heat from the wiring.
In areas not specifically designed for the installation of cables. e.g. service shafts and cavities, the cables shall be laid so that they are not exposed to am harmful influence by the normal operation of the adjacent installations (e.g. gas. water or steam lines).

Postby ericmark » Tue May 13, 2008 9:26 pm

Hello again Ceridwen I found a copy of the 16th Edition and the old regulations seem to have very little about hot water pipes as seem below:-
528-02-03 Where a wiring system is routed near a service liable to cause condensation (such as water, steam or gas services) precautions shall be taken to protect the wiring system from deleterious effects.
528-02-04 Where a wiring system is to be installed in proximity to a non-electrical service it shall be so arranged that any foreseeable operation carried out on either service will not cause damage to the other.

In real terms one must consider if the proximity of the pipes causes any real dangers. Putting control boxes under boilers where during maintenance water is likely to be split would not be sensible but the feed cable to the box is reasonability water proof and I can see no problems.

As to gap with cable to cable 300mm is normally considered so no interference transfers from low voltage (230v) to extra low voltages cables fire alarms etc. But this is hardly valid for pipes. I was told for years I should not water in same ducts as power cables but I can’t find any regulations to say that I think you need to use your special powers a Ceridwen is a witch is she not am sure you can persuade him!

It has said for whole day there is a reply but it seems the modulators are busy and it has not arrived yet.

All best Eric

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