522.6.203 RCD protection required for cables in metal stud walls, what about ceilings?

Prospective list of codes:

• No RCD protection to domestic lighting circuits- C3

• No RCD protection for cables concealed in walls- C3

• No RCD protection for circuits supplying bathroom- C3

• No RCD protection for cables in metal partition- C2

• No visible supplementary bonding in bathroom where lighting and fan circuit is not RCD protected-C2

versus:

• 30 mA RCD main switch-C?

would you code the single upfront RCD?


Andy B

Now, why would one code an upfront RCD as anything? It is fully compliant although if a fault occurs may not be convenient.

Your bathroom list, is the fan or light fitting in a zone, and which? Bonding may well not be visible, you check the earth resistance with a meter and check it meets 415.2.2. There is no requirement for supplementary bonding to be in a particular position (701.415.2), as long as it is present (low resistance value, it is adequate). Remember bonding is only required if the metalwork is extraneous to the bathroom, isolated items (or plumbing with plastic pipes) do not need any. Items needing bonding must be able to introduce a potential into the bathroom from somewhere else. If the light fitting is plastic or class 2 it doesn't require bonding, similarly the fan.


Your list of potential C2 defects is now looking a bit thin. Do you really have a metal partition, or do you mean that it has metal studs? If so which regulation is breached by a lack of earthing this structure? Perhaps you are concerned that a cable (sheathed, so mechanically protected) might somehow contact the frame, and then someone put an exposed screw into the frame potentially allowing them to receive a shock? The frame is not an exposed conductive part, or an extraneous conductive part, so where is this coming from? Note that BS 7671 explicitly states that metal fittings which are isolated do not require bonding. You recently asked if metal ceiling parts need bonding. Again they are generally isolated metalwork, and light fittings which may be attached are Earthed anyway. Earthing continuity in the average suspended ceiling would be difficult to arrange, and in any case, is not required.

Metal stud partitions do not require earthing, cables in them require 30 mA RCD protection.


701.401.3.6 distinguishes between serving the location and zones within a bathroom, in a bathroom or shower room you need 30 mA RCD protection for circuits:

(i) serving the location 

(ii) passing through zones 1 and/or 2 not serving the location.


 Andy B.

The main issue with metal stud partition walls is someone like me - the installer - When I want to install a new switch or socket because I've created a meeting room in an office space that was open plan - what do I do?


I get my 25mm hole saw - or others may get a 10mm drill and poke my head above the ceiling and drill down into the wall. Install lighting cable. I used to use SWA and now use BS8436 but I've often seen twin and earth dropped down to the switch. 


If I want a new socket - I drill upwards from the floor with a 90' drill (I'd always use a 25mm hole saw but its common to see a 10mm drill having been used - and there's no way to fit mechanical protection to that hole. - In a completed plaster board wall and you're installing a socket at some future point)


I always use BS8436 on a B type MCB now - used to use SWA - but its common again - to see twin and earth being use streight off the underfloor non RCD protected underfloor bus bar. 


Hence - I've always reasoned - why that reg came to be.................

I suspect a live wall, that comes down to the level of kitchen and bathroom furniture , washing machines etc is actually far more dangerous than a live ceiling, unless  the ceiling is low, or the occupants are girraffes.


Ceilings and ceiling voids are a bit of a free for all regulation wise - cables in joists are regulated, cables between them less so.

If you are standing on steps to reach the ceiling you will not be so well earthed, Though I suppose some folk will stand in the sink to change the lamps.


However,  it is not uncommon to see T and E skinned to the core by sharp metal edges and gorrilla installers, so there is some wisdom in adding RCD protection if it is practical to do so.

A reminder of the supplementary bonding requirements before RCD protection.

Sparkingchip, that was the 15th or perhaps the 14th edition which went mad on bonding. Really it had nothing to do with RCDs or not, and was reversed in the 16th because many of the suggestions were more dangerous rather than less. Putting consumers in a conductive location is definitely a bad idea as any shock will be much more serious. This particularly applies to commercial kitchens, where excessive local bonding and earthing makes them a death trap. Large areas of Earthed metal and a damaged cable are not recommended. RCDs do give some additional safety, as does limiting the earthed metal available to touch. Plastic piping is definitely an electrical safety measure, perhaps BS7671 should specify it?

I presume the room into the top left has an electric fire bonded to the central heating,  which is completely over the top. But if we are going into a home wired in the 1980's isn't that what we should be expecting to find if nothing has not been updated?


The problem is that the bathroom had probably been updated with the supplementary bonding being ripped out,  but the fuse  board has not been upgraded and RCD protection added.


It's digressing from the original post,  but when people say that lacking RCD protection to bathroom circuits is a C3 the bonding has to be in place to avoid a C2, so adding a RCD becomes the easiest way to upgrade. 


Andy B

That drawing could almost be my house, but there seem to be no gas pipes; and why is that baguette above the wash hand basin not bonded?