Mechanical protection

[GaryMo]

Question can we use flexible or pliable conduit - short answer no, BUT - why, the sheath is robust enough to stay intact and support fault current flow until the protective device operates (a basic requirement not always met by BS 8436 cables) AND, the major objection to the use of this conduit as a protective conductor is that it may fail due to movement BUT, it is in a wall and will not move.

What advice would you give? This is where you earn your money .

The reliance is upon the gland twisted against the conduit so would this connection be accessible for inspection?

 

[NotHimAgain]

Would you want a conduit socket to be accessible? .

 

[GaryMo]

Question can we use flexible or pliable conduit - short answer no, BUT - why, the sheath is robust enough to stay intact and support fault current flow until the protective device operates (a basic requirement not always met by BS 8436 cables) AND, the major objection to the use of this conduit as a protective conductor is that it may fail due to movement BUT, it is in a wall and will not move.

Would you want a conduit socket to be accessible? .

I can't see it being accessible so another reason why not to use flexible conduit within a wall to avoid the requirement of additional protection, as if 543.2.1 wasn't enough.

 

[NotHimAgain]

I can't see it being accessible so another reason why not to use flexible conduit within a wall to avoid the requirement of additional protection, as if 543.2.1 wasn't enough.

So what about flushed in or concealed screwed barrel conduit then - that's allowed and that has sockets .

In objecting to the use of flexible conduit you need to be sure that you are not just doing so because we always have. If an additional cpc is inserted in the conduit earth integrity would be improved, and if we insisted that the flexible conduit be connected to earthed metal boxes at both ends of its run, we have significantly reduced the risk from a loose termination. If we add to that quality control for the terminations we may just be there.

The art of being a consultant is, for the appropriate fee, to be able to appear to tell the client that they can do what they have asked without actually taking responsibility .

With that in mind (and given that I have a very expensive PI insurance policy) I can tell the large contractor that this MAY be a reasonable approach (of course it MAY not, and if you pay me enough I'll prove it ).

If I was asked the same question by a small contractor with limited financial (my fee ), technical and legal resources - I would probably say - no 543.2.1 precludes it

 

[GaryMo]

So what about flushed in or concealed screwed barrel conduit then - that's allowed and that has sockets .

As you said, that's allowed (543.2.2(vi))......

In objecting to the use of flexible conduit you need to be sure that you are not just doing so because we always have.

I'm objecting to it because it's specifically forbidden if an installation is to comply with BS7671 (543.2.1). If you choose to use flexible conduit as a CPC then it would need to be noted as a deviation from BS7671.
If something goes wrong then you would need a good reason why you chose to use a non-compliant product when there were many other compliant products available though I suppose you'll say that's where a consultant earns his money - I prefer to keep things simple.

 

[NotHimAgain]

I'm objected to it because it's specifically forbidden if you're installation is to comply with BS7671 (543.2.1). If you choose to use flexible conduit as a CPC then it would need to be noted as a deviation from BS7671.
If something goes wrong then you would need a good reason why you chose to use a non-compliant product when there were many other compliant products available.

Well your not wrong of course, but in the example I have given there was no suitable alternative and, in any event, the contractor was a big boy who could look after himself .

However, leaving aside BS 7671 - what is the technical objection to the use of flexible conduit in the way I have described above?

 

[GaryMo]

However, leaving aside BS 7671 - what is the technical objection to the use of flexible conduit in the way I have described above?

I see where you're coming from though an internal cpc won't help matters as 522.6.6(i) is specifically looking for an earthed metallic covering so this would be down to the spiral.
At a guess I would say it was added to 543.2.1 for two reasons, one being the insecurity of the glands to create a sound electrical connection and another being that the spiral can be pulled apart leaving open spots which I've seen on many occasions in industry.
I agree that within a wall it's not likely for the gland to become loose nor the spiral to be pulled open.

 

[NotHimAgain]

Just finally - I included the internal cpc to remove any concerns regarding failure of the flexible conduit as a protective conductor, as in 'earth wire' - not to meet the 522.6.6 earth screen requirements.

 

[GaryMo]

Just finally - I included the internal cpc to remove any concerns regarding failure of the flexible conduit as a protective conductor, as in 'earth wire' - not to meet the 522.6.6 earth screen requirements.

So you're concerned about the failure of flexible conduit?
In that case, is it really suitable for 522.6.6(i)?

 

[NotHimAgain]

I am not concerned - I only told them it MAY be a reasonable approach. If the conduit fails I will say it wasn't .