installing cables through joist where 50mm not possible

[amateurSparky]

well that video was conclusive. I'll check if it's acceptable to just notch it. Then I'll put warning tape along the piece of floor board going on top of the joist. That's the best I can do really. It's for a socket point used by unskilled/ instructed person so under the regs it has to be RCD protected anyway.

The communite responsible for the regs haven't done anything about it so what can I do?

 

[RF Lighting]

https://www.youtube.com/watch?v=dFfIrTTFfFc

Well, I imagine that the nail gun is probably more powerful than me and my hammer!

So, what do you conclude - given that a nail gun can apparently shoot nails through steel conduit, and the fact that most (if not all) standard steel conduit has a wall thickness less than this oft-quoted 3mm figure, do you feel that steel conduit does not afford enough protection to satisfy BS7671?

Kind Regards, John

Plenty of people lay floors with nail guns. I think I have some 3mm steel plate. I'll try again with that.

Steel conduit is ok even if it can be penetrated, as it's earthed, so causes ADS. Safe plates are not, so must prevent penetration.

 

[JohnW2]

Plenty of people lay floors with nail guns. I think I have some 3mm steel plate. I'll try again with that.

Bated breath I doubt whether you'll get through 3mm plate unless you have a very powerful gun and some very hard nails, but I may be wrong!

Steel conduit is ok even if it can be penetrated, as it's earthed, so causes ADS. Safe plates are not, so must prevent penetration.

Well, whilst I agree that it's sort-of OK, electrically, ('sort-of',since prevention of cable damage is obviously preferable to damage and ADS), the regs are a different matter. 522.6.100(vi) and 522.6.101(iv) explicitly require "mechanical protection sufficient to prevent penetration of the cable by nails, screws and the like." There is no mention of any relaxation of this requirement to prevent penetration in the presence of ADS. You therefore may be about to demonstrate that cables in standard steel conduit are not compliant with BS7671 !

Kind Regards, John

 

[RF Lighting]

https://www.youtube.com/watch?v=I6P2QPJB24I


Looks like steel conduit is none compliant then, and a 3mm steel plate is the answer.

 

[JohnW2]

https://www.youtube.com/watch?v=I6P2QPJB24I Looks like steel conduit is none compliant then, and a 3mm steel plate is the answer.

Technically speaking, that does seem to be the case, although you're presumably going to upset a good few of your colleages by suggesting/demonstrating that steel conduit can be argued to be technically non-compliant! Mind you, there is the only-too-common vagueness in BS7671 - if you used hard enough nails and a powerful enough gun, you'd undoubtedly be able to get through 3mm plate as well.

In terms of notched joists (after all, relevant to the subject of this thread), a practical problem with 3mm protection is that it would, in many/most cases, require time-consuming woodwork to enable the floorboard to sit flush with its siblings (and without wobbling!). With ~1mm one can usually get away without that and,if my own experiments are valid, seems to be adequate protection against nails and hand tools.

Kind Regards

 

[amateurSparky]

lets hope someone from the commmunite can put forward our scientific arguement.

 

[JohnW2]

lets hope someone from the commmunite can put forward our scientific arguement.

Which argument do you think should be put forward - that standard conduit is not acceptable?

Kind Regards, John

 

[amateurSparky]

sorry just had a look in my onsite guide but am still confused. Does the span of th joist mean the entire length of joist? The socket in question is in the top front room. So is it the length between the exterior wall at the front of the property to the dividing wall ( one that divides the front and back rooms) ?

 

[EFLImpudence]

Wall to dividing wall.

 

[JohnW2]

Wall to dividing wall.

That presumably assumes that the dividing wall is 'weight-bearing'?

Kind Regards, John

 

[EFLImpudence]

I knew you'd say that. That's why it took over two hours for a reply.

Is it not bound to be?
If it weren't, would there not be a space between wall and joist and rather bouncy?

I think it unlikely that the joists run from front to back in one length but...

 

[JohnW2]

I knew you'd say that. That's why it took over two hours for a reply.

Well, the 'span' is obviously the distance spanned between supports. If it's is not supported by the 'dividing wall', then the span is between the end supports.

Is it not bound to be?

"Bound to be" is dangerously close to those 'never'/'always'/'none'/all' words that I was taught never to use! When I moved into my present house, many moons ago, I wanted to remove a ground-floor wall. Since it was solid (proved to be 9" brick) I was concerned that it might have been supporting (at roughly mid-point) the floor joists above. However, I did some exploratory removal of cornice/coving and, to my joy, discovered that they were concealing a 2" gap (just 'thin air') between the top of the brick wall and the joists above!

If it weren't, would there not be a space between wall and joist and rather bouncy?

That 'depends'. They don't make houses like wot they used to - IIRC, the joists in question were roughly 9" x 3" (or maybe even 12" x3" - I have some of those!) - and don't bounce at all

I think it unlikely that the joists run from front to back in one length but...

If it's a 20th century build, I agree that it's unlikely.

Kind Regards, John

 

[EFLImpudence]

Yes. I keep forgetting.

I shall have to preface all my posts, or have a signature, stating -

'assuming your house is typical of the majority - excludes castles and stately homes'.

 

[JohnW2]

Yes. I keep forgetting. I shall have to preface all my posts, or have a signature, stating -
'assuming your house is typical of the majority - excludes castles and stately homes'.

Maybe, but I think you also need to think about the other end of the spectrum - in which some 'dividing walls' are so flimsy that they wouldn't offer significant support to any joists which may pass over them! I'm no authority on such things, but I think the classic design for an 'ordinary house', with a solid load-bearing wall in the middle, has probably become much less prevalent in the last half a century. I would also add that one certainly does not need either a castle or a stately home (mine is certainly neither ) to have characteristics such as I described - merely one that was built prior to the 20th century.

Kind Regards, John

 

[Scoby_Beasley]

Obviously a 1mm plate is less penetrative than I thought!

Specify tungsten carbide steel hardened to 45-49 rockwell.

You'll be safe but a lot poorer!!!