Chasing cable in a ceiling

[Richard Burns]

Effectively the cable is run above a very thin layer of the ceiling i.e. the plaster covering the cable.
The cable itself is not protected against penetrative impacts such as nails and screws.
There is no indication that the cable is present as it has been plastered over.
A significant possibility exists that the ceiling may need to be repaired or an item may need to be fixed to a ceiling within the lifetime of the installation.
In the case of someone working on or at the ceiling, since it is not possible to identify that the cable is there, someone may damage the cable inadvertently, giving rise to the possibility of electric shock.
This is something that is to be avoided in the installation of a cable and there are no options specified to prevent this for your cable type and installation location.
Whilst approved document P can be a little woolly in its wording it does state that electrical installations should be designed to comply with BS7671.

 

[Wilko]

Hi - a bit of overnight thinking, for what it's worth. The technique seems novel and seems not specifically referenced to either exclude or include in BS7671, that I could see. However, that doesn't mean BS7671 doesn't apply or has nothing to say. Being concerned about impact to the cable that is now part of the ceiling Chapter 52 Selection and Erection of Wiring Systems seems relevant. Reading 522.6 Impact, it begins as an inclusive statement and so applies in this case, IMHO. Section 522.6.1 says "shall be erected to minimise damage from mechanical stress". Then 522.6.2 says "protection shall be afforded by characteristics of the wiring system". At present what you describe does not satisfy these directives. IMHO a fit for 6.1 could be to have it buried out of harms way and not fixed and concealed just mm below the surface. Or for 6.2 could be to make it using steel conduit or SWA.

 

[Deleted member 26818]

No it is not specifically referred to in BS7671, because it's not really a viable option.
BS7671 requires that cables should be protected against impact, abrasion, penetration, tension or compression.
One method is to run cables above a ceiling, ensuring that if a cable passes through a joist, that it is more than 50mm from the surface of the ceiling, mechanically protected against penetration from nails or screws, etc, etc.
This cable has not been run above a ceiling so another method of protection is required.
Other methods are earthed sheath, conduit or trunking, mechanical protection or by placing the cable in a location where it will not suffer any damage.
Concealing the cable within the fabric of the ceiling would only comply if there is a guarantee that no one would ever pierce the cable.
So somewhere that no one would put a hanging basket, punch bag, decorative plaster casts, model airplanes, hanging seats, friparies to hang over a bed, Christmas decorations, speakers, fly paper, insectocuters, etc, etc.

 

[Gigsy]

E
Whilst approved document P can be a little woolly in its wording it does state that electrical installations should be designed to comply with BS7671.

I think you may be referring to the approved document which explains how to comply with Part P of the building regulations. Can you show mw where in the actual building regulations, in Part P, it refers to BS7671?

 

[Leesparkykent]

I think you may be referring to the approved document which explains how to comply with Part P of the building regulations. Can you show me where in the actual building regulations, in Part P, it refers to BS7671?

pages 3,4,9,10 and 12 of approved document P

 

[Gigsy]

pages 3,4,9,10 and 12 of approved document P

The approved document is not Statutory Law, just a guide to help you comply with the law. The building regulations on the other hand are the law. This is what is actually written in The Building Regulations and what is on the statute books,


"PART P ELECTRICAL SAFETY


Design and installation


P1. Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installation from fire or injury."


I just hate the way you electricians quote regulations and documents, half the time not related to the particular installation being discussed, and make it out that you are quoting law and scaring people into thinking they are breaking the law and acting unlawfully, when in fact you know very well that approved documents and wiring regulations are not law and purely guidelines.


I believe my cable is safe as it is protected by an RCD. If an unprotected cable run under plaster less than 50mm in a wall is considered safe, because it has RCD protection, then I say a cable run in a ceiling, less than 50mm under plaster is equally as safe.

 

[Leesparkykent]

 

[Pat H]

Page 3 references it. As does page 4. Also on 9 10 and 12.

 

[Gigsy]

Hi - a bit of overnight thinking, for what it's worth. The technique seems novel and seems not specifically referenced to either exclude or include in BS7671, that I could see. However, that doesn't mean BS7671 doesn't apply or has nothing to say. Being concerned about impact to the cable that is now part of the ceiling Chapter 52 Selection and Erection of Wiring Systems seems relevant. Reading 522.6 Impact, it begins as an inclusive statement and so applies in this case, IMHO. Section 522.6.1 says "shall be erected to minimise damage from mechanical stress". Then 522.6.2 says "protection shall be afforded by characteristics of the wiring system". At present what you describe does not satisfy these directives. IMHO a fit for 6.1 could be to have it buried out of harms way and not fixed and concealed just mm below the surface. Or for 6.2 could be to make it using steel conduit or SWA.

Section 522.6.1 says "shall be erected to minimise damage from mechanical stress".

"In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other" wikipedia

My cable is not under any stress.

protection shall be afforded by characteristics of the wiring system

Yes, an RCD

 

[Gigsy]

No it is not specifically referred to in BS7671, because it's not really a viable option.
BS7671 requires that cables should be protected against impact, abrasion, penetration, tension or compression.
One method is to run cables above a ceiling, ensuring that if a cable passes through a joist, that it is more than 50mm from the surface of the ceiling, mechanically protected against penetration from nails or screws, etc, etc.
This cable has not been run above a ceiling so another method of protection is required.
Other methods are earthed sheath, conduit or trunking, mechanical protection or by placing the cable in a location where it will not suffer any damage.
Concealing the cable within the fabric of the ceiling would only comply if there is a guarantee that no one would ever pierce the cable.
So somewhere that no one would put a hanging basket, punch bag, decorative plaster casts, model airplanes, hanging seats, friparies to hang over a bed, Christmas decorations, speakers, fly paper, insectocuters, etc, etc.

BS7671 requires that cables should be protected against impact, abrasion, penetration, tension or compression.

BS7671, is therefore in breach of it's own rules, because it allows a cable to be run less than 50mm in a wall, under plaster when protected by a RCD. If it is good enough for the goose it is good enough for the gander. If they consider it to be safe in a wall, then I consider it to be safe in a ceiling.

 

[Wilko]

Section 522.6.1 says "shall be erected to minimise damage from mechanical stress".

"In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other" wikipedia

My cable is not under any stress.

protection shall be afforded by characteristics of the wiring system

Yes, an RCD

If you believe you are compliant with building regulations then that's great, but surely you would only know if you requested a building reg person to assess and approve your work?

 

[Gigsy]

If you believe you are compliant with building regulations then that's great, but surely you would only know if you requested a building reg person to assess and approve your work?

I think I may give them a call, thank you.

 

[Andy78]

So in a nutshell

OP: I've done something I think might not be right, what do you lot think ?
Forum: We think it is not right
OP: Well what do you lot know, why don't you all shut up ?

Quality thread.

 

[Deleted member 26818]

BS7671 requires that cables should be protected against impact, abrasion, penetration, tension or compression.

BS7671, is therefore in breach of it's own rules, because it allows a cable to be run less than 50mm in a wall, under plaster when protected by a RCD. If it is good enough for the goose it is good enough for the gander. If they consider it to be safe in a wall, then I consider it to be safe in a ceiling.

That is not the case at all.
Cables concealed in walls at a depth less than 50mm must be:
a) run in prescribed routes and
b) provided with RCD protection.
Providing RCD protection without running the cable in a prescribed route is not acceptable.
As has already been explained, there are no prescribed routes on a ceiling.

 

[Gigsy]

So in a nutshell

OP: I've done something I think might not be right, what do you lot think ?
Forum: We think it is not right
OP: Well what do you lot know, why don't you all shut up ?

Quality thread.

I didn't say shut up, I simply corrected some miss-information.