'Safe Zone' created by 'current using equipment' ??

[JohnW2]

No EFLI I disagree. Not determined by where the cable emerges from the wall but rather in line with the borders of said accessory/point/switchgear. Does the mirror qualify as any of those? Does an electric shower qualify? If not then what the heck do you do?

That's what most of us have decided and said.

However, getting back to your comment about "the letter of the reg", and despite what most of us think and have said, I'm not at all convinced that a shower qualifies as "a point, accessory or switchgear", does it? If not, it would (per "the letter of the reg") not generate any zone(s) in which one was permitted to bury ('#unprotected') cables!

Kind Regards,John

 

[ebee]

Hmm i think you might have the kernel of a good idea in that one.
However, does anyone at all bury 6.0 or 10.0 T&E shower cable more than 50mm deep or use armoured/earth sheathed cable? Id suggest not but just stick to the usual zones in practicei

 

[JohnW2]

Hmm i think you might have the kernel of a good idea in that one. ... However, does anyone at all bury 6.0 or 10.0 T&E shower cable more than 50mm deep or use armoured/earth sheathed cable? Id suggest not but just stick to the usual zones in practicei

I very much doubt that (m)any people do - but, as I wrote, whether or not what they are doing is compliant with "the letter of the regs" (you're phrase ) may perhaps be a different matter!

Kind Regards, John

 

[ebee]

It all rather depends upon the interpretation of points,accessories and switchgear and this must be done in accordance with BS7671, section 2 definitions should be the ultimate reference on that score prior to any other references we might draw upon.

If said mirror does not fall into any category (or an electric shower, for example) then we have a problem.
If we decide they do not tgen we have a problem, do we exercise sound engineering judgement to treat the mirror or the shower as similar arrangements in respect of the zones or do we take extra precautions in depth or armouring or conduits etc knowing that, in practice, it will cause further problems on a potentially massive scale?

Let's say we decide they are treated as the same, then without guidance to state otherwise we must treat the whole of mirror/shower external dimensions as creating the zones and the boundaries of such zones. If guidance is given to assume the effective "point of connection" is within a certain area insides and our mirror/shower unit, unless the manufacturer actually states otherwise then we would need such manufacturers to adopt a national and international consensus, i do not envisage that being a possibility..

Taking the example of the humble twin socket then the boundary is defined by the socket dimension itself not just tge backbox it is mounted in , OK only a very few mm but that does define the zones and whilst cables might be going in straight/level lines from box to box we can not guarantee that it is not meandering towards the zone bounderies.

 

[EFLImpudence]

This is all ridiculous postulating about a problem that does not exist.

Has anyone ever fitted an illuminated bathroom mirror, or similar, before installing the cable for it?

 

[JohnW2]

It all rather depends upon the interpretation of points,accessories and switchgear and this must be done in accordance with BS7671, section 2 definitions should be the ultimate reference on that score prior to any other references we might draw upon.

Exactly.

If said mirror does not fall into any category (or an electric shower, for example) then we have a problem. ...

Indeed. My very point, and ....

If we decide they do not tgen we have a problem, do we exercise sound engineering judgement to treat the mirror or the shower as similar arrangements in respect of the zones or do we take extra precautions in depth or armouring or conduits etc knowing that, in practice, it will cause further problems on a potentially massive scale?

.... again, the very point I recently made. As I wrote yesterday, it's only very recently occurred to me that the authors of BS7671 might have deliberately decided that IF there are no "points, accessories or switchgear" (per its definitions0 on a wall, then cables are not permitted to be buried (>50mm) in that wall without armour/conduit/whatever.

So, as you say, the question is whether something like a mirror qualifies (per BS7671 and its definitions) as a "point, accessory or switchgear". I imagine that we can agree that such an item is not an accessory or switchgear, so that the only discussion is about whether or not it is a "point".

However, as I've said, even if we DID decide that a mirror qualifies as 'a point', I'm not sure that would help much. As I've said, a point is a point, and I can't see that it's meaning can be extended to relate to something very much larger than that point - so I also cannot see that one can interpret the reg in any way other than saying that the 'permitted zones' (for buried cables) created by a 'point, accessory or switchgear" have dimensions dictated by the dimensions of the "point, accessory or switchgear" itself, can you?

Kind Regards, John

 

[JohnW2]

This is all ridiculous postulating about a problem that does not exist.

All I'm trying to do is to ascertain the intended interpretation of a reg in BS7671 under certain circumstances, which I wouldn't say was a ridiculous desire.

Has anyone ever fitted an illuminated bathroom mirror, or similar, before installing the cable for it?

One can argue about what 'fitted' means, but we can agree that it can't be connected to it's electrical supply until the cable has been installed.

However, one could say/ask exactly the same about any accessory or switchgear (switch, socket, FCU, CU etc.e etc.). One installs the cable(s) first, BUT with route(s) that will be permitted ones once the accessory or switchgear is subsequently 'fitted' (and connected).

If one first installed the cable, and then installed the associated accessory or switchgear in a position which did not create a 'permitted zone' where the cable had been installed, then the cable route would then obviously not be compliant. Nor is that only hypothetical - I recently saw a case in which exactly that had been done, leaving nearly all of the cable supplying a new socket outside of the 'permitted zone' created by the position in which the socket had been installed.

 

[EFLImpudence]

All I'm trying to do is to ascertain the intended interpretation of a reg in BS7671 under certain circumstances, which I wouldn't say was a ridiculous desire.

Well, I think it so obvious, I really don't know why there would be any doubt.

One can argue about what 'fitted' means, but we can agree that it can't be connected to it's electrical supply until the cable has been installed.

Exactly.

However, one could say/ask exactly the same about any accessory or switchgear (switch, socket, FCU, CU etc.e etc.). One installs the cable(s) first, BUT with route(s) that will be permitted ones once the accessory or switchgear is subsequently 'fitted' (and connected).

Of course -

but surely the backbox (or similar) will usually be positioned first.

If one first installed the cable, and then installed the associated accessory or switchgear in a position which did not create a 'permitted zone' where the cable had been installed, then the cable route would then obviously not be compliant.

Obviously.

Nor is that only hypothetical - I recently saw a case in which exactly that had been done, leaving nearly all of the cable supplying a new socket outside of the 'permitted zone' created by the position in which the socket had been installed.

GETAWAY! You're having me on!

Was it debated by a gathering of experts or was the solution obvious to all concerned?

 

[ebee]

Yes I too have seen cables installed with tails left hanging out then boxes mounted so that the cables were then out of zones - never underestimate the determination of complete fools. PS all done by the same person

 

[EFLImpudence]

Right, so let us start again:

A back box or just a cable exiting the wall - the red square - is to be installed at a position that will be hidden by the illuminated mirror.
The cable for this mirror will obviously have to be installed before the mirror is hung (not to mention before the wall is tiled) so it will not be there.

So, instead of chasing the wall and fitting the cable vertically or horizontally from the red square in the shaded grey areas, you two are saying that it would be compliant with the regulations and perfectly understandable to chase the wall and install the cable where any of the red lines is - or any infinite number of other similar routes.

Really???

 

[JohnW2]

Well, I think it so obvious, I really don't know why there would be any doubt.

If you think the answer is "so obvious", why do you not give us your view as to what that answer is? ....

You want to install an illuminated mirror (say 700 x 500 mm, a common size) in a known position on a wall. For simplicity, let's say that there are no other 'electrical items' visible anywhere on the wall.​

Where (if anywhere) are you permitted (by BS7671) to bury 'unprotected' cables <50mm below surface on that wall ?​

​

Of course - but surely the backbox (or similar) will usually be positioned first.

Usually", yes, but not inevitably. Possibly not in the case I describe below.

GETAWAY! You're having me on!

I can but report what I saw with my own eyes....

... a double socket had been installed, presumably fairly recently, since the wall had not be re-decorated such that the routes of the chases could be seen. There was a nice, neat and straight vertical chase all the way down from the ceiling. However, instead of going into the top of the back box, it went down to the midpoint (vertically) of the socket, some 3 or 4 inches to the side of the socket, then turned through 90 degrees and then travelled horizontally to enter the backbox from the side - so that only the last 3-4 inches of the cable was in a permitted zone created by the socket.

I have no idea why that was done (nor whether the backbox was installed before the cable) - the property was unoccupied when I saw it, with no knowledge of previous occupiers or of anything to do with the installation of the socket. The issue has now been resolved, simply by moving the socket to 'where it should be' (relative to the buried cable)..

The fact that something should not be done is no guarantee that no-one will ever do it!

Was it debated by a gathering of experts or was the solution obvious to all concerned?

I don't understand that question. I have merely reported what I saw - no 'debate'with anyone was involved.

 

[EFLImpudence]

If you think the answer is "so obvious", why do you not give us your view as to what that answer is? ....

WHAT?

 

[JohnW2]

Right, so let us start again: ..... A back box or just a cable exiting the wall - the red square - is to be installed at a position that will be hidden by the illuminated mirror. .... The cable for this mirror will obviously have to be installed before the mirror is hung (not to mention before the wall is tiled) so it will not be there.
So, instead of chasing the wall and fitting the cable vertically or horizontally from the red square in the shaded grey areas, you two are saying that it would be compliant with the regulations and perfectly understandable to chase the wall and install the cable where any of the red lines is - or any infinite number of other similar routes.

You have merely produced a variant of the diagram I posted in #26.

I was not "saying that it would be compliant" to have the cable buried in any of the routes shown by red lines in either of our diagrams - it was surely obvious that I posted my diagram to indicate that I would consider it daft IF that were permitted by the regs.

By including in your diagram (in grey) the 'permitted zones' that would be created by a backbox if it were visible, what do you think that adherence to those zones would achieve when the box was not visible?

... and what if the cable simply came out of a half-inch diameter 'hole in the wall'. Ignoring the fact that that point would again not be visible, how 'wide' do you think the permitted zones would be in that case?

 

[JohnW2]

WHAT?

I'm still waiting for your answer to the question that I have just re-posted.

 

[EFLImpudence]

Oh FFS I despair.