RCD Protection on 16mm Submain??

[Paul Chick]

Hi all

House C/U is in the kitchen, come off the mains blocks into a KMF isolator then across above the plasterboard ceiling about 15m in 16mm T&E into the the new granny annex C/U. This is the way I have always done it, depending on the circumstances. If it was SWA I wouldn't be having this issue but I would struggle getting that in. So... is that stupid little green book now telling me I have to put some sort of 30ma protective device at the start and how does that work out in regards to the 2x RCDS in the granny annex C/U. Time delayed RCD maybe? Does my head in, should have been a chippy...


:mad2:

 

[telectrix]

RCD protection is required if cable is <50mm deep buried in walls without earthed mechanical protection. does that answer the q.?

 

[Deleted member 26818]

I take it, you are refering to the requirement to provide additional protection for cables concealed in walls.
From your description of the route, the cable is not concealed in any walls.
As such additional protection is not required.

 

[malcolmsanford]

If you bury the T & E less than 50mm in a wall then you do have to provide it with additional protection either by RCd or some form of earthed containment as per regs.

But if you have it surface up a wall then across the ceiling it only need normal protection either by MCB/Fuse

 

[Paul Chick]

It was a flat roof so they had to drop the ceiling a couple inches with baton so i could get it across then put board over it. Technically its not buried but on the other had you cant see it.

If you bury the T & E less than 50mm in a wall then you do have to provide it with additional protection either by RCd or some form of earthed containment as per regs.

But if you have it surface up a wall then across the ceiling it only need normal protection either by MCB/Fuse

 

[malcolmsanford]

Have a look at reg 522.6.100 concerning a cable installed under a floor or above a ceiling and it will tell you that it does not need additional protection

But as Tel, Spin and I have said in a wall less than 50mm then you do need to provide that additional protection as per 522.6.101

 

[Deleted member 26818]

It was a flat roof so they had to drop the ceiling a couple inches with baton so i could get it across then put board over it. Technically its not buried but on the other had you cant see it.

The requirement is to provide additional protection for cables concealed in walls.
There are requirements for additional protection for cables concealed in ceilings or under floors, but none require the provision of RCD protection.
You are required to provide additional protection at any point where the cable passes through a batten or joist, which could be provided by use of steel plates, or short lengths of conduit. Use of an RCD would not be an acceptable method.

 

[Guitarist]

I think the problem we have here is that the distribution cable is an inch above the new ceiling and either sitting on it, or clipped to the new battens which have been put up to hold said new ceiling. It's ok quoting regs until someone decides to screw a new light fitting into that ceiling and goes through the T&E.
In this case, as the cable is hidden and extremely close to the surface, I would personally either use swa or mechanically protect it. All down to what YOU, as the designer, feel is appropriate though.

 

[sedgy34]

As you say it's ok to regs

 

[truckster]

I think the problem we have here is that the distribution cable is an inch above the new ceiling and either sitting on it, or clipped to the new battens which have been put up to hold said new ceiling. It's ok quoting regs until someone decides to screw a new light fitting into that ceiling and goes through the T&E.
In this case, as the cable is hidden and extremely close to the surface, I would personally either use swa or mechanically protect it. All down to what YOU, as the designer, feel is appropriate though.

Agree with Guitarist, unless you can get 50mm above the surface of the ceiling it requires addition protection.

 

[Deleted member 26818]

I think the problem, is that people are under the impression that RCDs are the ultimate solution when providing additional protection.
This is simply not the case.
For cables concealed above a ceiling or below a floor, the use of an RCD is not an acceptable method of providing additional protection.
Install one by all means, as long as it complies with Section 314.
Do not then make the mistake of beliving that you are able to omit providing the additional protection as required by Regulation 522.6.100.

 

[Guitarist]

I think the problem, is that people are under the impression that RCDs are the ultimate solution when providing additional protection.
This is simply not the case.
For cables concealed above a ceiling or below a floor, the use of an RCD is not an acceptable method of providing additional protection.
Install one by all means, as long as it complies with Section 314.
Do not then make the mistake of beliving that you are able to omit providing the additional protection as required by Regulation 522.6.100.

Agree mate. Proper protection for a cable cannot be substituted with an RCD.

 

[Gordon]

Regs require RCD for cables in walls without earthed mechanical protection. Steel conduit or SWA for a distribution circuit do not require RCD as long as they are earthed.

 

[Paul Chick]

It would have been ok because the builder told me that the ceiling was going to be dropped about 60mm give or take, but on returning a couple weeks ago he decided to dropped it about 30 without letting me know an now its been boarded and plastered! Where does this leave me know guys, bit worried about this one.

Cheer

Paul

 

[Welchyboy]

i would personally not sit comfortable without RCD on that sub main it is not safely installed and would be easily penetrated

if it was a lighting cable i would maybe let it go.....begrudgingly but a 60A submain....no chance, i would prefer to protect the whole install from the origin of the submain on one 30mA than not, if someone decided to overboard that ceiling in years to come they may get a nasty surprise!

one thing ive learnt is not to pay any attention to what builders tell you they are gonna do, they will always do whats easiest for them at the time, always install with that in mind, then you cant go wrong

 

[Guitarist]

It would have been ok because the builder told me that the ceiling was going to be dropped about 60mm give or take, but on returning a couple weeks ago he decided to dropped it about 30 without letting me know an now its been boarded and plastered! Where does this leave me know guys, bit worried about this one.

Cheer

Paul

Walk away.

 

[Paul Chick]

Im going to just have to put a 30mA RCD at the origin now regardless of reg 314 and just make a note. Really naffed off with this.

 

[Guitarist]

I feel for you mate. Are you obliged to do anything?

 

[Ponty Massive]

Could you not put a Type S RCD at the source, then have your dual RCD's in the board?

 

[Deleted member 26818]

Im going to just have to put a 30mA RCD at the origin now regardless of reg 314 and just make a note. Really naffed off with this.

To reiterate:
The use of an 30mA RCD is not an acceptable method of providing additional protection for cables above ceilings or under floors.
Unless you also provide an acceptable method, you will fail to comply with both 314.1 and 522.6.100.