17th Edition - RCD requirements and concealled cables

[Spark123]

Looking through the 17th edition there is a requirement to protect cables such as twin and earth which are buried less than 50mm from the surface with a 30mA RCD.
RCD protecting the whole installation is a bad idea as a single fault will cause all the lights to go out.
This leaves a some options, installing a dual RCD board with main isolator (I think hager make them) spreading the lighting circuits and socket circuits between the two RCDs, or installing a normal split load board with the sockets etc on the RCD side, utilising RCBOs for the non RCD side for items such as lights (6A RCBOs not being the most readily available part yet.)
Whats everyone elses take on this?

 

[ban-all-sheds]

Well I'll toss in the point that interested me.

The requirement for such protection is "where the installation is not intended to be under the supervision of a skilled or instructed person.."

An "instructed person" is one who is "adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create."

The danger here is drilling etc into concealed cables.

If you leave clear documentation with the installation which identifies where all the concealed cables are, then the owner of the installation has been adequately advised, and is therefore, for the purposes of 522.6.6, an instructed person.

Discuss.

 

[plugwash]

my question would be what constitutes adequately advised. Is just leaving documentation sufficiant or do you need to make sure that they have read and understood the documentation, have a system for filing it sensiblly, are not in a declining mental condition etc.

BTW are cables with a built in earthed metal layer exempt from this rule?

 

[Spark123]

Interesting point. A couple of problems I can see should the documentation is lost or the person moves out. How can you ensre the transfer of the responsibility to the next owner?

 

[Spark123]

BTW are cables with a built in earthed metal layer exempt from this rule?

Yeah, subject to it being suitable as a CPC.
edit
also if you can mechanically protect the cables from penetration of screws, nails and the likes.

Looks like concentric cables have been dropped from the regs for this, also for underground use.

 

[daytona]

good point BAS


maybe we could write a letter to a client explaining safe zones,or leave definitions of such by consumer unit(fixed obviously)and say that all wiring is contained within these zones.after that surely client has to take responsibility for his/her actions.

explaining to them the cost issues with rcbo protection and nuisance tripping,it doesnt take a genius to work out what they will go for!

if that is the official stance,then i can see a new sticker coming out

 

[dingbat]

If you leave clear documentation with the installation which identifies where all the concealed cables are, then the owner of the installation has been adequately advised, and is therefore, for the purposes of 522.6.6, an instructed person.

From the horses' mouths (note plural) it is not envisage that a domestic installation could ever effectively be deemed to be under the supervision of a skilled or instructed person.

That is the message that attendees of 2382 courses will be given.

 

[mst]

Does anyone know where you can buy dual RCD boards yet?

 

[RF Lighting]

An electrical wholesaler would be my first port of call. Think dual tarrif, and RCDs

 

[Norv]

Looking through the 17th edition there is a requirement to protect cables such as twin and earth which are buried less than 50mm from the surface with a 30mA RCD.

Will this still be a requirement if all the cables are fitted in the safe zones ?

 

[RF Lighting]

It looks like it

 

[ban-all-sheds]

Interesting point. A couple of problems I can see should the documentation is lost or the person moves out. How can you ensre the transfer of the responsibility to the next owner?

How can you ever ensure that people in the future do what they should?

You're required to identify circuits - if you do that and in the future someone rips the labels off, is that your fault?

If in the future someone changes an MCB for one with an inappropriate rating, is that your fault?

If in the future someone discards the documentation of where the cables are, is that your fault?

Note - the regulation says (I'm quoting from Wiring Matters here, not the actual red book as I don't have that yet) "where the installation is not intended to be under the supervision of a skilled or instructed person..".

So if you do as Daytona says, and ensure that you explain the issues (it doesn't take a genius to understand the risks of drilling into cables, I'm sure that householders will grasp that), and ensure that you leave details of where the cables are, then you clearly intend that the installation is to be under the supervision of an instructed person, and therefore you've complied with the regulations.

New builds, rented accommodation, commercial etc is different, but for a customer in their own home...

And what about me? I believe I am a skilled person, and therefore my installation does not need that additional RCD protection to comply with the 17th. I don't intend moving, so I intend that the installation will be under my supervision.

Any electrician could likewise legitimately certify his own installation as compliant with the 17th.

But what if he moves out? What is the mechanism for invalidating the previously valid EICs? Right up to the point where he moves out and hands over the keys the installation is under his supervision. When does the EIC become invalid? When he puts the house up for sale?

How is a change in the person supervising the installation any different from any other deterioration in it which makes an EIC which was valid when it was issued, invalid?

 

[Lectrician]

My regs are under dust sheets due to wall removal...

Anyone care to look in 2008's deffinition list for 'Instructed Person'?

 

[ban-all-sheds]

From the horses' mouths (note plural) it is not envisage that a domestic installation could ever effectively be deemed to be under the supervision of a skilled or instructed person.

That is the message that attendees of 2382 courses will be given.

That may be the message that they are given, but it is clearly not what the regulations say.

Understanding "it is unsafe to drill/screw/nail/chisel/bite/whatever into electrical cables" is not hard.

Understanding "this is where the cables are" is not hard.

It does not take much to make someone "adequately advised".

 

[ban-all-sheds]

Does anyone know where you can buy dual RCD boards yet?

Hager have been making them for years.