cables in stud walls what are the 17 edition requirements

[tombainbridge1]

bear with me im a carpenter, so im only vaguely aware of electrics

is it correct that in steel stud walls that that grommets are needed. is this to protect the insulation of the cables and to stop the studs becoming live? Is either or both correct?

how should cables be fixed in either timber or steel stud walls if at all?. do they need to be clipped to the nearest stud or does the need for cable runs to run vertically mean they have to dangle loose in the void with no clipping at all?

as more and more stud walls have to be sound insulated it means that i see cables are pushed against the back of the plasterboard. im again vaguely aware that cables in brick walls need to be in conduit if they are less than 50mm deep.

however ive not seen conduit in stud walls, is there a reason?

 

[EFLImpudence]

is it correct that in steel stud walls that that grommets are needed. is this to protect the insulation of the cables and to stop the studs becoming live? Is either or both correct?

Grommets are needed, primarily to protect the cable but obviously you do not want the studs to be come live.

how should cables be fixed in either timber or steel stud walls if at all?

It depends - see below

do they need to be clipped to the nearest stud or does the need for cable runs to run vertically mean they have to dangle loose in the void with no clipping at all?

They may. It depends - see below.

as more and more stud walls have to be sound insulated it means that i see cables are pushed against the back of the plasterboard.

It is greatly detrimental to the Current Carrying Capacity of the cable to run 'through' insulation so should be clipped to the studs or, at least, against the plasterboard (there would still be some derating of the CCC).

im again vaguely aware that cables in brick walls need to be in conduit if they are less than 50mm deep.

If protected by a Residual Current Device they do not need to be in earthed metal conduit but if run 'outside the safe zones' then they either do or have to have some other earthed metal protection.

however ive not seen conduit in stud walls, is there a reason?

You won't see much metal conduit these days. Plastic conduit is for convenience only. It does not offer protection.

 

[ban-all-sheds]

If protected by a Residual Current Device they do not need to be in earthed metal conduit but if run 'outside the safe zones' then they either do or have to have some other earthed metal protection.

There's not much "if" about it with walls with metal studs - with those you must have either RCD protection or metal conduit etc, irrespective of how deep or where the cables run.

 

[EFLImpudence]

If protected by a Residual Current Device they do not need to be in earthed metal conduit but if run 'outside the safe zones' then they either do or have to have some other earthed metal protection.

There's not much "if" about it with walls with metal studs - with those you must have either RCD protection or metal conduit etc, irrespective of how deep or where the cables run.

Anyway - OP was asking about brick walls in that part of the post.

 

[PrenticeBoyofDerry]

is it correct that in steel stud walls that that grommets are needed. is this to protect the insulation of the cables and to stop the studs becoming live? Is either or both correct?

both are correct, grommets should be used or some form of protection for the cable, this could be by means of conduit.
Most metal stud dry-ling systems, now have pre-installed service holes that are cut out or push. Cable still most be routed in .
the safe zones

how should cables be fixed in either timber or steel stud walls if at all?. do they need to be clipped to the nearest stud or does the need for cable runs to run vertically mean they have to dangle loose in the void with no clipping at all?

Ideally depending on type and section of the cable they should be fixed at pre-designed distances/spaces, to reduce stress to cable, assure they stay in the correct position, so they do comply to the safe zone and keep in complaints to the fixed reference method for de-rating.

as more and more stud walls have to be sound insulated it means that i see cables are pushed against the back of the plasterboard. im again vaguely aware that cables in brick walls need to be in conduit if they are less than 50mm deep.

As above the positioning of the cable, will give reference code to the method the cable has been fixed, this is know as a "reference method", this will when designing the circuit inform you of what current any given type of cable can carry safely when fixed and installed using different containment in different locations and in different environments.
eg a 2.5 mm T&E cable, surface clipped, directly to a wall and run between a consumer unit and a socket outlets, can carry a higher current capacity than the same cable over the same distance between the CU and socket outlets, when the cable is routed in a thermal insulated wall and in conduit.
A de-rating factor must be applied.
This is quite an important factor and is covered in more detail in these publications:
BS7671:2008
OSG amendment out soon
electrician guide to building regulations

however ive not seen conduit in stud walls, is there a reason?

Conduit can be useful for a lot of applications and is really handy for re-wiring of circuits but depending on the circumstances it is not always used or needed.