College tutor - rcd issue

[gazdkw82]

My tutor at college is really good. Explains things well and is very knowledgable. He has mentioned a few times that the use of RCD’s doesn’t comply with the regs. By this he means that in the regs it states that rcds cannot effect other circuits upon operation.

So the use of rcds protecting more than 1 circuit is not in occordance to bs7671.

As my tutor explains, if I was to be standing in the dock having to explain why, when the rcd tripped on the downstairs sockets it tripped the upstairs lights and led someone to fall down the stairs and die, they would just point to this reg and I wouldn’t have anyway out of it.

I get it but, they are so widely used in this way. In the fact the only real to avoiding this is rcbo’s. If you quoted every rewire or board change on just rcbos you would hardly get any jobs because Alan the electrician down the road can do a split board with rcd protection at half the cost.

Sometimes I feel this industry is a little contradicting or unrealistic

 

[Ian1981]

If each circuit required individual rcd protection then you would imagine this would be a regulation in itself ie where a circuit is required to be protected by a rcd be it for additional protection and or fault protection , individual protection shall be afforded and no other circuit shall be affected by the operation of the rcd etc, or words to that effect maybe?

Circuits shall be arranged to minimise nuisance tripping which by splitting your circuit arrangements is achieved by a dual rcd board.
Perhaps rcbo individual circuits are better but not necessarily the only way to comply

 

[Edtwozeronine]

One thing I can say is that generally it's considered standard practice to front load RCDs before MCBs, cos that's the cheapest way to do it. You should be able to stand up in court and say millions of homes consumer units are set up this way, even if the regs state they shouldn't be.

In the past if we had a power cut I could always put my hands on a torch or candle. These days there's the torch app on your dog and bone too.

There is a call to get rid of ring circuits in the 18th Edition, I bet the majority of houses won't be updating their wiring to comply with that though.

 

[Ian1981]

One thing I can say is that generally it's considered standard practice to front load RCDs before MCBs, cos that's the cheapest way to do it. You should be able to stand up in court and say millions of homes consumer units are set up this way, even if the regs state they shouldn't be.

In the past if we had a power cut I could always put my hands on a torch or candle. These days there's the torch app on your dog and bone too.

There is a call to get rid of ring circuits in the 18th Edition, I bet the majority of houses won't be updating their wiring to comply with that though.

There’s no future plans at least not in the recent public draft of the 18th edition to prohibit ring final circuits and why would there be ?

 

[Edtwozeronine]

Just hear-say ATM, it's what I heard. (Oh, and I heard it about mid-way through last year from my Tutor - before any drafts were out I'll wager)

 

[Ian1981]

On thing I do know is that at the moment AFDD don’t work on ring finals(what I’ve read and seen anyways) so if they eventually become mandatory then if the manufacturers can’t get them to work with rings then the ring final may become obsolete?
Just a thought

 

[SparkyChick]

On thing I do know is that at the moment AFDD don’t work on ring finals(what I’ve read and seen anyways) so if they eventually become mandatory then if the manufacturers can’t get them to work with rings then the ring final may become obsolete?
Just a thought

That's quite interesting... any info about why they don't work?

 

[Ian1981]

That's quite interesting... any info about why they don't work?

2 conductors in parallel I would imagine rather than your bog standard radial circuits where a potential break causing arcing is easier to detect.
There new so don’t know that much about them but the NICEIC did a webinar on the changes and this is what was pointed out

 

[Gavin John Hyde]

Personally i think your tutor is being a bit pedantic. Its often disputed whether BS7671 can even be produced in evidence as some judges have refused to allow it to be used by the prosecution as its a non statutory document. It seems a good barrister will have no issue with these things. if RCDS used in the above way were so risky, it wouldn't have been allowed.

 

[Edtwozeronine]

Yeah, at some point we were told we'd be in more trouble for not installing things according to manufacturer's instructions... In the world of work that is!

 

[gazdkw82]

Well I think your right, he did also say that if your gaffa asks you to install an rcd then do it but just ask him to consider RCBO.

I get what he’s saying but if it was so “wrong” then why is it taught in electrical training and why is it an accepted practice from the numerous governing bodies etc

 

[The Ghost]

And what reg. did he quote to support that statement? So we won't fit RCD for sockets or bathroom and when Mrs. x dies shall we get your tutor to get us out of hot water?

 

[MJPD29]

In that case why is the widespread use of split boards where all circuits are protected in 2 blocks by 2 rcds so common

 

[SparkyChick]

All the regs state I believe is in 314.

Every installation shall be divided into circuits, as necessary to:-
(i) avoid danger and minimise inconvenience in the event of a fault

There are other clauses, but this is the most relevant to the OP.

 

[Richard Burns]

The regulations do not make a specific statement that an RCD cannot be used to protect more than one circuit.
However they do make a statement that as far as is necessary that inconvenience should be minimised in the case of a fault by dividing the installation into circuits (nothing about RCDs).
It is the level of force that this regulation has that is subject to interpretation. In your case your tutor has decide that this is absolute down to circuit level, in most cases an assessment of the inconvenience is made and the level of inconvenience is considered to be minimised by the use of split RCDs.
To take the consideration further you would be applying RCBO protection to individual accessories, which would be better compliance with the minimisation of inconvenience, but (even though this is now it is getting closer, as there are more and more circuits in an installation but the same load) we are not quite at that level of minimisation.
There has to be a balance between practicality and perfection, this is what the regulations are saying, but where that balance lies is open to differing interpretations.