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

[JohnW2]

Perhaps we could start with the common case of a wall mounted extractor fan. Does the extractor fan create safe zones above, below and to both sides which are the same width and height as the extractor fan?

If we're talking about a standard 4"or 6" fan, then, like Murdo, I would say 'yes', since that''s not much different from an electrical accessory.

However, if it were a mega-fan, say 2 feet square, I think I would be back to my question!

 

[JohnW2]

But in the case of , for example an oven, the safe zone is dictated by where the cable exits the wall

An oven would not usually be 'fixed to a wall' in the same sense as other things we've been discussing - but, if it were, there would still be the issue of 'dimensions' ...

If the cable came out of the wall within an accessory, say 90 x 90 mm, then that would be straightforward - both horizontal and vertical 'zones' would then be 90 mm wide. But what if the cable literally 'exits the wall' through a half-inch diameter hole - are the zones then only half an inch wide?

... this is essentially the problem when a zone is defined by 'a point', rather than 'an accessory of switchgear'.

 

[Murdochcat]

But what if the cable literally 'exits the wall' through a half-inch diameter hole - are the zones then only half an inch wide?

.

Just stop being stupid

 

[JohnW2]

In an attempt to bring some sanity to this discussion, I think we are agreed that there are two sides to the story - one based on common sense and the other relating to regulations:

1... For the person with a drill in their hand, if there is a large electrical item fixed to a wall with nothing to indicate where the cable supplying it is routed, common sense dictates that they have no alternative but to assume that the cable could be buried 'almost anywhere' - certainly possibly anywhere within zones above/below/to the side of the appliance, with dimensions per those of the appliance.

2... For the person installing the cable, there is a requirement to comply with BS7671's 'rules' as to where buried cables may be located. It is far from clear what those rules really are when the appliance is large, but I don't think it makes much sense to believe that the intended interpretation is that the cable can be installed anywhere (including 'diagonally' in zones such I have depicted in post #26 - so it's difficult be sure what is the intended interpretation in such a situation.

My present situation is more straightforward, since I don't yet have an appliance (mirror) to install. I therefore will run the cable to some accessory (presumably a back box with blank plate), within zones defined by that accessory, 'in the usual way'. That will be fine, and meaningful, until .the mirror is installed, but will cease to be a useful indicator (to 'the man with a drill') of cable routing once the accessory ceases to be visible - but there's nothing I can do about that. However, I will document the cable route, and make sure that that documentation is made available to any 'men with drills', at least for as long as the property is under my control .

 

[JohnW2]

Just stop being stupid

Not stupid at all. I have at least a couple of examples in my house of cables which literally just 'exit a wall' through holes not much bigger than themselves.

 

[JohnW2]

IMHO Yes because you have no idea where the cable entry is AND cables need to be run vertically or horizontally

I think you'll find (I don't have it immediately to hand) that the reg does not actually say that the cables have to be run horizontally or vertically - I think it says that the zones have to be horizontally and vertically aligned to whatever is creating them, the implication being that the cable can 'wander about' as much as it likes provided it remains within the (horizontal or vertical) zone it is in.

Zones created by accessories are pretty narrow, so the cables have to be fairly close to horizontal or vertical, but that all changes if the zones are very much wider.

 

[ebee]

Well in my opinion, example, electric shower, the "safe zone" should be horizontal or vertical in alignment with the whole of tge width or height of that shower heater case it self. The ordinary person can not be expected to remove the cover to see where the actual conductors enter the back of the shower.
As an electrician, i would usually run it in alignment to the point of entry of the backplate or close nearby if there's a spray head rail to go in that position.
Its proper term of "zone of protection" to my mind the protection is being where gained from any person having a thik about where such cable might be run.
In practice i do not favour horizontal zones although they are permitted I am pretty much a vertical only practitioner.

 

[EFLImpudence]

In an attempt to bring some sanity to this discussion,

You started it.

1... For the person with a drill in their hand, if there is a large electrical item fixed to a wall with nothing to indicate where the cable supplying it is routed, common sense dictates that they have no alternative but to assume that the cable could be buried 'almost anywhere' - certainly possibly anywhere within zones above/below/to the side of the appliance, with dimensions per those of the appliance.

Is that not what was originally said which you have been disputing all along and causing the insanity?

2... For the person installing the cable, there is a requirement to comply with BS7671's 'rules' as to where buried cables may be located. It is far from clear what those rules really are when the appliance is large, but I don't think it makes much sense to believe that the intended interpretation is that the cable can be installed anywhere (including 'diagonally' in zones such I have depicted in post #26 - so it's difficult be sure what is the intended interpretation in such a situation.

Of course not. Only you have suggested such a thing.

My present situation is more straightforward, since I don't yet have an appliance (mirror) to install. I therefore will run the cable to some accessory (presumably a back box with blank plate), within zones defined by that accessory, 'in the usual way'. That will be fine, and meaningful, until .the mirror is installed, but will cease to be a useful indicator (to 'the man with a drill') of cable routing once the accessory ceases to be visible - but there's nothing I can do about that. However, I will document the cable route, and make sure that that documentation is made available to any 'men with drills', at least for as long as the property is under my control

Of course.

 

[JohnW2]

Well in my opinion, example, electric shower, the "safe zone" should be horizontal or vertical in alignment with the whole of tge width or height of that shower heater case it self. The ordinary person can not be expected to remove the cover to see where the actual conductors enter the back of the shower.

As I said in relation to the small (4"/6") fans, I totally agree with you, in relation to a shower.

As far as 'the man with a drill' is concerned (which, despite what some people seem to think, is NOT what I was asking about), there is little doubt that they have to assume that a buried cable might be in any of the areas you mention. However, what the regs regard as a permitted route for cables in that situation (which IS what I was asking about), seems far less clear, since a 'shower heater case" is not 'a point', 'an accessory' or 'switchgear'.

However, as I also wrote when talking about the small fans, when one moves to a much larger object attached to the wall (mirror etc.) I am far less sure about what the regs intend as a 'permitted cable route' - although, again, 'the man with a drill' has no choice but to accept that cables could be anywhere to the sides or top/bottom of the entire width /height of the object.

As an electrician, i would usually run it in alignment to the point of entry of the backplate or close nearby

As I've said, so would I - although I accept that such would be of no help to a subsequent 'man with a drill'who did not know where that 'point of entry was.

As I've suggested, if the regs wanted to address this situation, I suppose they could do something like defining 'permitted zones' of specified width radiating horizontally and vertically from the centre of the visible object.

In practice i do not favour horizontal zones although they are permitted I am pretty much a vertical only practitioner.

Fair enough, that';s your choice, but it would be a bit of a pain when (as commonly in kitchens and workshops etc.) there were several sockets all at the same (above counter/workbench) height around the walls. I must say that I can't see a problem with horizontal cables in such a situation, since to just run the cables 'from socket to socket' would seem the most obvious thing, which most people (including those 'with a drill in their hand') would probably assume to be the most likely situation.

Kind Regards, John

 

[JohnW2]

You started it.

I started by asking specifically (and only) what people thought BS7671 intended to be permitted routes for buried cables in certain circumstances, NOT what a a person 'with a drill in their hand' had to assume to be possible routes of buried cables.

Is that not what was originally said which you have been disputing all along and causing the insanity?

It has indeed been said, but I have repeatedly been trying to point out that, as above, that was NOT what I was asking about. I was asking specifically and only about the interpretation of 522.6.202 when the appliance in question is very large.

Of course not. Only you have suggested such a thing.

I've only 'suggested' it in order to demonstrate that it would seemingly be daft for BS7671 to be intending that - but, as I keep saying, it is not clear (at least, not to me) what 522.6.202 does intend in terms of 'permitted routes for buried cables' when the object in question is very large.

The bottom line is that people contributing to this discussion do not seem to understand (in relation to a large appliance fixed to a wall) the difference between:

1... What routes for buried cables does BS7671 permit? (which I DID ask)
and
2... Where 'a man with a drill' has to assume that cables might be buried (which I did NOT ask, because it has to be down to common sense).

 

[ebee]

I think we have to take heed that there can be sometimes be confusion over the word "point", it actually means a "point of utilisation" such as a socket (a single, twin, triple etc socket is1 point of utilisation).
Of course in ordinary life some might take it to mean a hole in the wall where a cable comes thru. And i certainly use that meaning for main bonding when considering the words "point of entry" there are often two actual points of entry for a bonding cable, especially on s double skinned wall, just outside the property the hole in the wall where the cable disappears into tge property is one and the corresponding place inside the property where that cable appears from on the inside. Obviously i prefer to have the earth clamp on the inside of the property all nice and dry and out of reach for some idiot to remove maliciously etc.

As with "safe zones" well you runs cables in those zones in the futile hope that the person with the drill looks at it and thinks "Hah , no I will not risk drilling there!" No they still conspire to drill the hole or hammer a nail in to hang that picture on the wall.

 

[JohnW2]

I think we have to take heed that there can be sometimes be confusion over the word "point", it actually means a "point of utilisation" such as a socket (a single, twin, triple etc socket is1 point of utilisation).

Indeed. In fact, in present context, I think the word "point" is worse than just 'confusing' since, I genuinely don't understand what (in relation to situations we're talking about) it is intended to mean in 522.6.202.

As I've said, if taken literally a point has no dimensions (is infinitely small) and therefore would create zones (in which one was permitted to bury cables) which were infinitely narrow. ... and it's not really as simple as you suggest above, because a socket (and other things) is already considered by the reg as an "accessory", so "point" is not relevant for such items.

This is very relevant to this discussion, since the sort of large items we're talking about (mirrors. TVs, boilers etc.) are certainly not (electrical) "accessories" or "switchgear", so if they are covered by 522.6.202,it can only be as "points"

As with "safe zones" well you runs cables in those zones in the futile hope that the person with the drill looks at it and thinks "Hah , no I will not risk drilling there!"

Indeed - but, as I've repeatedly said, and as I'm sure you understand, I have not been asking about the situation from that person's; point of view - I have merely asked for views as to where BS7671 permits cables to be buried (<50mm deep) in relation to large piece of current-using equipment attached to a wall - and no-one has really yet given me much of an answer to that question.

As for the 'man with a drill', the "safe zones" would cease to have much useful meaning if (per my silly diagram in post #26) that zone covered a large proportion of the wall. If the person had to drill a hole in the wall, he/she would therefore have to use some other method (other than guidance based on 'safe zones') to determine where cables were (or might be

No they still conspire to drill the hole or hammer a nail in to hang that picture on the wall.

Indeed. I can tell a story about my own stupidity .... a few decades ago I had a floorboard up for some reason, and there were a pair of copper CH pipes going along its length, in notches in the middle of the top of the joists. Having completed whatever I was doing, I replaced the floorboard and religiously/carefully secured it with nails which I made sure were well away from the centre of the board (hence pipes).

When I had put in all those nails 'near the edges of the board', I found that it was 'wobbling' a bit at one end. In some sort of auto-pilot mode, and clearly without much thought, I therefore took a nice long nail and a heavy hammer and hammered the nail in right in the middle of the wobbly end of the board ... the rest of the story does not need to be described

I have also, just once I think, drilled through a live electrical cable,but I really don't think I can be blamed for it. There were absolutely no electrical accessories (nor 'points' or switchgear!) anywhere on the wall I was drilling into, but it transpired that there was a cable buried in the entire height of the wall, being a feed for a lighting circuit from below the floor to above the ceiling!

Kind Regards, John

 

[securespark]

The only thing I think that can do this is a consumer unit.

 

[securespark]

When I was at college in the 80s, we we taught a point is where two or more cables are joined.

 

[JohnW2]

The only thing I think that can do this is a consumer unit.

In that case, I would say that it's very sensible. In fact, I think we've agreed that for relatively small 'electrical things' (including CUs, standard extractor fans etc.) it's very reasonable to say that buried cables may be buried in the horizontal and vertical zones created by the entire height and width of the visible object.

It's when the object gets much larger that the situation becomes less clear.