Cable in narrow space - how to fix it?

[bureaucrazy]

10mm 2+e must run in a 30mm wide gap under floor between wall and joist. Must also be >50mm from surface or enclosed in earthed metal or impenetrable armour. The distance is only 1m. It is not possible to reach 50mm down the gap to fix nail/screw in cable clips.

Would any of the following methods comply with the regs?

1. Rest a length of 25mm galvanised conduit on the ceiling at the bottom of the gap and push the cable through it. Attach an earth clamp and wire back to the consumer unit with 6mm earth. My concern here is that the cable nor the conduit is fixed although the cable would not suffer mechanical strain and it would not move if left undisturbed.

2. Use self-adhesive cable clips. My concern is that the adhesive may degrade over time or they do not meet the regs in the first place.

3. Make wooden supports and glue them to the joist at 30cm intervals so the cable can rest >50mm from the surface.

4. Screw cable tie mounts near the top of the joist as it can be reached using a tiny 90 degree screwdriver. Then use 2 cable ties for each interval: 1 loop long enough to go 50mm down the gap and another loop fastened to the cable. Here the cable will be suspended loosley in the right place. My concern is that this is improper use of cable ties and the cable will be loose.

5. Drill 2 small (<5mm diamter) holes through the joist at each interval to fix saddle clips by nut and long bolt. This violates the hole drilling rule for joists as they will not be in the correct zone, but in practice the tiny diameter holes would not weaken the joist.

6. Self adhesive mini trunking. Again, will the adhesive last stuck to the joist?

Are there any other solutions? There really is no other suitable route. How about just resting the cable on the ceiling? It is then supported by the ceiling. It is RCD protected.

Thanks.

 

[telectrix]

just drop it in resting on ceiling.make sure no insulation is stuffed on top.

 

[bureaucrazy]

What about it being <50mm from the surface? does it not matter? I guess from time to time, it's not practical to comply with every reg 100%?

 

[telectrix]

the 50mm guideline is mainly for under floors ( so as no nails or screws reach it). consider a rewire when you pull cables under floor. they all rest on ceiling unless you lift loads of floorboards to fix cables to joists.

 

[Wilko]

Agree with Tel. I'm assuming it's not protected by RCD - so would the flexible steel conduit help, supported at each end and earthed. Cheers, David.

 

[bureaucrazy]

It is RCD protected but there is no way to support the conduit. The conduit would have to rest without fixings on the ceiling.

 

[happysteve]

The 50mm rule is only necessary if the cable passes through a joist. It doesn't sound like yours does:

522.6.201: A cable installed under a floor or above a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or ceiling or their fixings.

A cable passing through a joist within a floor or ceiling construction or through a ceiling support (e.g. under floorboards shall):

(i) be installed at least 50mm measured vertically from...

So just rest the cable on the ceiling between the joist and the wall, assuming the provisions described in the first sentence are met.

 

[LankyWill]

it can be less than >50mm if its rcd protected. Slightly over thinking it mate

 

[happysteve]

It can be less than 50mm if it's not RCD protected, as long as it's not passing through a joist/ceiling support, and is run in a position that is not liable to be damaged by contact with the floor or ceiling or their fixings.

RCD protection doesn't come into play under floors or above ceilings, only in walls.

 

[Richard Burns]

I think overall you have a non problem here.
You have a run of cable that is protected by a 30mA RCD, the cable is being installed on top of a ceiling between a wall and a joist.
The cable will be free to move away (up) if there were to be a nail hammered through the ceiling so the chance of damage is not high. Were it to be damaged the cable is earthed and 30mA RCD protected.
There is no requirement to protect such a cable with a 30mA RCD and no constraints on the position of such a cable so you are compliant no matter what you do.

If you were all that worried about something you have not yet specified then you could use SWA cable instead as this would have an earthed covering, or you could just slot a 25x50 batten into the space and lay the cable on that.

 

[westward10]

I agree with Richard you are trying to find a solution for a problem which doesn't really exist.

 

[bureaucrazy]

Thanks very much for the replies. I mistakenly thought the cable must at all times stay >50mm from the surface and must be clipped along the joist if running the same direction. I see now that it is OK to rest it on the ceiling and the 50mm rule is specific to cables passing through holes in joists as that is the only place likely to be nailed into. In fact there are pictures in the OSG section 7.2 showing cable resting on ceiling. Many thanks, I am happy with the easy way.