Unperforated cable tray.

[Dee J]

For a property I'm working on right now, some unperforated steel cable tray would be very useful.. logistically it would be vey convenient if floor/ceiling cable runs could be <50mm from the plasterboard surface, and a unperforated steel tray would fulfil both the required of protecting the cables in close proximity to the surface and providing a fire-resistant cable support. Such stuff does exist... just can't find a convenient uk supplier yet. Can anyone recommend?

Thanks

Dee

[ProDave]

Why unperforated?

 

Standard perforated cable tray is available from electrical wholesalers, most will deal with cash customers, certainty CEF will, there must be a branch of them near you.

[Dee J]

Yes. That's just it. Perforated is easily available, but doesn't provide appropriate protection for cables <50 mm from the plasterboard surface. Ie a plasterboard fitter could easily drive a screw through a hole in the tray and the cable without hitting the earthed steel first. Unperforated unistrut may well do the job, but it's just a bit on the narrow side.

[ProDave]

What protection are you talking about?

 

Are you trying to find a way to avoid the need for RCD protection?  If so forget it. Just use perforated and rcd protect all your circuits.  It is almost unheard of now to fit any new circuit without rcd protection.

 

In any case the <50mm rule for rcd protection only applies to walls, not ceilings. It is to prevent damage from someone hanginf say a picture on the wall, something you don't typically do on a ceiling.  Any cable damage during the build will be found on the final testing in any case.

 

If this is not your reasoning, then what other 50mm rule are you referring to?

[Dee J]

A quick google suggests 522.6.201 as requiring cables to be >50 mm above the ceiling or to be protected. (Physically, not just rcd). Haven't got my new blue book in front of me right now.

Edited February 19, 2019 by Dee J

[ProDave]

I think you are  misinterpreting that.  >50mm or physically protected or in safe zone AND rcd protected.

 

ALL of a ceiling is a safe zone, safe zones apply to walls.

 

If you are really worried use perforated tray and set it >50mm above the ceiling.  Don't over think it.

[Jeremy Harris]

51 minutes ago, Dee J said:

A quick google suggests 522.6.201 as requiring cables to be >50 mm above the ceiling or to be protected. (Physically, not just rcd). Haven't got my new blue book in front of me right now.

 

 

Edited to add:

 

Here's whole of the relevant section from the the blue book:

 

Quote

522.6  Impact (AG)

522.6.1  Wiring systems shall  be selected and erected so as to  minimize the damage arising from  mechanical stress, e.g. by  impact, abrasion, penetration, tension or compression during installation, use or maintenance.

522.6.2  In  a fixed  installation where  impacts of medium  severity  (AG2) or high  severity  (AG3) can occur protection shall  be afforded  by:

(i)  the mechanical characteristics of the wiring system, or

(ii)  the location selected, or

(iii)  the provision of additional local  or general  protection against mechanical damage, or

(iv)  any combination of the above.

NOTE:  Examples are areas where the floor is likely to be penetrated and areas used by forklift trucks.

522.6.3  Not used

522.6.4  The  degree of protection of electrical equipment shall be maintained after installation of the cables and conductors.

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 50  mm measured vertically from the top, or bottom as appropriate, of the joist or batten,

or

(ii)  comply with  Regulation 522.6.204.

522.6.202  A cable installed  in  a wall  or partition  at a depth of less  than  50  mm  from  a surface  of the  wall  or partition shall:

(i)  be installed in a zone within ISO  mm from the top of the wall or partition or within  ISO mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear. Where the  location of the accessory, point or switchgear can be determined from  the  reverse  side,  a  zone  formed  on one  side of a  wall  of l 00  mm  thickness or less or partition of l 00  mm thickness or less extends to the reverse side, or

(ii)  comply with  Regulation 522.6.204.

Where indent (i) but not indent (ii) applies, the cable shall be provided with additional  protection by  means of an RCD having the characteristics specified in  Regulation 415.1.1.

522.6.203  Irrespective of its buried depth, a cable concealed  in a  wall or partition, the internal construction of which includes metallic parts, other than metallic fixings such as nails, screws and the like, shall:

(i)  be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1,or

(ii)  comply with Regulation 522.6.204.

For a cable installed  at  a  depth  of less than  50mm  from the surface of a wall or partition  the requirements of Regulation 522.6.202(i) shall also apply.

522.6.204  For the purposes of Regulation 522.6.201 (ii), Regulation 522.6.202(ii) and Regulation 522.6.203( ii), a cable shall:

(i)  incorporate an earthed metallic covering which  complies with  the  requirements of these  Regulations  for a  protective conductor of the  circuit  concerned,  the cable  complying with  BS  5467,  BS  6724,  BS  7846, BS 8436 or BS EN 60702-1 , or

(ii)  be installed  in earthed conduit complying  with BS  EN 61386-2  and  satisfying the  requirements  of these

Regulations for a protective conductor, or

(iii)  be enclosed in earthed trunking or ducting complying with BS EN 50085-2-1 and satisfying the requirements of these  Regulations for a protective conductor, or

(iv)  be  provided  with  mechanical  protection against damage  sufficient to  prevent  penetration of the cable  by nails, screws and the like, or

(v)  form part of a SELV or PELV circuit meeting the requirements of Regulation 414.4.

 

522.6.201 looks to be essentially the same as the wording in 522.6.100 in the 17th Ed to me, in that it applies to cables going through a joist, where they have to be either >50mm from the edges or be protected as in 522.6.204.  Looks like all they've done in the 18th is to move things around, so that the distance requirement and the protection requirement are now in different paragraphs.

Edited February 19, 2019 by JSHarris
Added section from the 18th Ed

[Dee J]

The situation I have is a floor-ceiling structure of closely spaced heavy joists (which would be a pain to drill), which for other reasons (complicated underfloor heating) has been counterbattened underneath. This gives a great runway for wiring, but every point it crosses a joist the wiring is held within 25 mm of the plasterboard. These crossing points are where I run foul of the regs above.... 

[ProDave]

This is no different to wiring within the confines of a 25mm or even 50mm deep service void.

 

As long as the cables are in safe zones, you have no issues.  so just choose the wiring routes so they are in safe zones.

[Dee J]

14 minutes ago, ProDave said:

This is no different to wiring within the confines of a 25mm or even 50mm deep service void.

 

As long as the cables are in safe zones, you have no issues.  so just choose the wiring routes so they are in safe zones.

The service void is in the ceiling.... and the safe zones are where?

[Jeremy Harris]

5 minutes ago, Dee J said:

The service void is in the ceiling.... and the safe zones are where?

 

There aren't separate safe zones in ceilings, only in walls.  This post has the relevant pages from the OSG:

 

 

[ProDave]

6 minutes ago, Dee J said:

The service void is in the ceiling.... and the safe zones are where?

The whole ceiling.

[Dee J]

3 hours ago, JSHarris said:

522.6.201 looks to be essentially the same as the wording in 522.6.100 in the 17th Ed to me, in that it applies to cables going through a joist, where they have to be either >50mm from the edges or be protected as in 522.6.204.  Looks like all they've done in the 18th is to move things around, so that the distance requirement and the protection requirement are now in different paragraphs.

 

1 hour ago, ProDave said:

The whole ceiling

These two quotes seem contradictory... 

[Ed Davies]

Yes, there aren't safe zones in the ceiling as such but for cables installed in the ceiling the rules are pretty much as per being in safe zones in a wall so it's a reasonable short-hand to say the whole ceiling is a safe zone.

 

Differences, I can see: a) cables going though joists in the ceiling need to be at least 50 mm in & b) cables in wall safe zones need to be RCD protected (but that's hardly likely to matter as the cable's likely to need to be RCD protected anyway).

 

As written the regulations seem to require network cable in the safe zones not in conduit to be RCD protected but I'd have though the coils in an RCD would make all the bits dizzy and useless.