Safe zone for cable

[JohnW2]

Yes, there will always be a small element of uncertainty if the cable is, or stays, within the cable zone.

It will obviously vary a lot between different properties and different situations. In the case of my house, far from there being "a small element of uncertainty if the cable is, or stays, within the cable zone" I would say that it is very probable that many, maybe even most, of the cables in stud walls stray out of the prescribed zones.

I have a lot of accessories on 'stud walls' (mainly lath & plaster ones) and it would seem that nearly all the cables have a considerable amount of slack - so I'd probably actually be at least a little surprised if (at least, when 'vertical') they remain in the prescribed zones throughout their length.

Often, if someone decides to clip the cable down the stud, this will nearly always mean the cable can't be in-line with the plasterboard box. I try to avoid clipping them, for the reason, but I will fit a clip somewhere near where the box will go - and yank the cable from the clip before cutting the box in.

That 'yanking', and the 'clipping', (in an attempt to minimise slack) is something which very often seems not to be done, and certainly that is the case in my house.

One solution to all this may be to fit the boxes on noggins before boarding, and possibly use rigid 20mm plastic round conduit, held in place by the timber.

Rigid conduit obviously solves the problem, but (at least in my experience) rarely done, and sometimes impractical - the nearest equivalent to 'boarding' in my house is the lath & plaster that was applied about 130 years ago, and the place has been wired/re-wired a good few times since then

Kind Regards, John

 

[JohnW2]

To avoid discussing the wrong problem, the wall in question is dot and dab.

My comment didn't relate to the OP's situation. It was a general observation about the way in which some people regard minor deviations from 'safe zones', given that the uncertainties which often exist within stud walls and the like.

Now, John, carry on with re-writing the wiring regulations.

I don't think the regs need re-writing, since what they specify about the 'zones' seems perfectly reasonable. However, the point I've been making is that those who intend to 'penetrate walls should regard those rules as no more than 'general guidance', and should remain aware of the possibility that concealed cables may exist significantly beyond the boundaries of those zones.

Pipes buried in walls, particularly in old buildings, are more of a problem, since there is often no equivalent of an electrical accessory to give any clue that a 'buried pipe' is beneath the surface of a wall. I fairly recently re-learned that the hard way

Kind Regards, John

 

[Murdochcat]

Bottom line is that the vast majority of DIYers and other trades don’t know about or recognise safe zones

 

[JohnW2]

Bottom line is that the vast majority of DIYers and other trades don’t know about or recognise safe zones

That's undoubtedly true. One certainly can never be totally confident when penetrating a wall, anywhere, with anything.

The only time I can recall having penetrated a cable it was miles from any electrical accessories (in fact, no accessories at all on the wall in question) and with absolutely no reason to suspect that there might be a cable there.

 

[pcaouolte]

In my own home, built in the 1970's there are diagonal cables to wall lights and one cable from the consumer unit (in the garage) to the upstairs lighting circuit which runs up a bedroom wall with no accessory to indicate it's position. The only cable that has been damaged was on a wall directly above a light switch (so in a 'safe zone') where someone had installed a picture hook with a nail which went straight through the switch cable, this was found on inspection when I moved in. Everything still worked as the nail had passed through the CPC without catching L or N.

 

[bernardgreen]

Cables that have been installed diagonally ( out of safe zones ) can go undetected for years if not decades. They are sometimes only found when things go badly wrong.

A friend was installing a new curtain rail in his lounge when with a Flash Bang Wallop the drill hit the 7/.044 cable that fed the kitchen. Christmas Eve, most inconvenient.

A neighbour had a shocking experience with a metal shelf bracket when cleaning the shelf. A screw fixing the bracket to the wall had pierced a cable and was in contact with the Live conductor. Fell and broke her wrist, several hours in A&E

 

[JohnW2]

In my own home, built in the 1970's there are diagonal cables to wall lights and one cable from the consumer unit (in the garage) to the upstairs lighting circuit which runs up a bedroom wall with no accessory to indicate it's position.

Similar here, other than that most of my house was build in the 1890s (a bit in the late 1700s. The one cable I damaged was travelling vertically up a wall (which, as I said, had NO visible electrical accessories at all) vertically from below floor level on ground floor up to a higher floor.

Kind Regards, John

 

[Harry Bloomfield]

Pipes buried in walls, particularly in old buildings, are more of a problem, since there is often no equivalent of an electrical accessory to give any clue that a 'buried pipe' is beneath the surface of a wall. I fairly recently re-learned that the hard way

For metal pipes at least, where there is any doubt, use a cable and pipe locator. I generally know where all of my cable pipe runs are, but still use a locator to precisely tie their locations down.

 

[JohnW2]

For metal pipes at least, where there is any doubt, use a cable and pipe locator.

I always do these days, and they are relatively foolproof in relation to metal pipes, less so with cables.

generally know where all of my cable pipe runs are, but still use a locator to precisely tie their locations down.

I also "generally know" in my house but, as I have illustrated, particularly in old houses there is always the potential for 'unexpected surprises'!

Probably the greatest such 'unexpected surprise' in my house arose when, soon after we moved in, a guy was installing a boiler in a small room in a corner of the house, and had to make a hole through the external wall for the flue pipe.

From the very start, there was a lot of bad language coming from the guy, since it was clearly a fairly thick wall - effectively a cavity wall with a 9" outer leaf and a 4.5" inner one. However, the language got far worse when we discovered that, within the 'cavity' was a sheet of steel about 1" thick !!

We do not know the explanation for sure. However, we have subsequently learned that the 'little room' in question was probably once "the butler's silver store" - so I suppose it's possible that they felt the need to anticipate someone demolishing the wall from outside to get at the 'silver'

Kind Regards, John

 

[Jupiter01]

No.

If the cable falls out of line from being within the prescribed cable zones because there is dot of plasterboard adhesive in the way, this is not acceptable.

You would have to make some slots of notches in the plasterboard for the cable to ensure the cable is within the zones.

I appreciate this is the write thing for you to write but do people actually do this?? It will need an additional hole(s) to be punctured into the plaster and then made good.

 

[Jupiter01]

In this case the OP is proposing to shove the new cable behind some existing dot and dab fixed plasterboard and hope that it will form a nice L shape where it changes direction from vertical to horizontal. It should also magically float in a perfectly horizontal position behind the plasterboard without any fixings. We all (including the OP) know that isn't going to happen.

What should I be doing at the junction of the horizontal to vertical run? Else, I could have a diagonal cable run

 

[Murdochcat]

Plumbers hiding plastic pipes in walls can cause untold misery too .......

 

[pcaouolte]

I appreciate this is the write thing for you to write but do people actually do this?? It will need an additional hole(s) to be punctured into the plaster and then made good.

Yes, people do this.

What should I be doing at the junction of the horizontal to vertical run? Else, I could have a diagonal cable run

You shouldn't have a diagonal cable run.

If you cut a neat hole in the plasterboard (with a multi tool if you have one) you can control the change of direction from horizontal to vertical, clip the cable in position and replace the piece of plasterboard with very little filling required. If the runs are not too long a single hole in the plasterboard at the point where you want the cable to turn through 90 degrees will probably be enough.

 

[JohnW2]

What should I be doing at the junction of the horizontal to vertical run? Else, I could have a diagonal cable run

As has been said, you mustn't have a diagonal cable run.

As has also been said, the only real way of dealing with the change from horizontal to vertical would be to make a hole in the plasterboard there (which can subsequently be 'made good' and wallpapered over, if that's what you want).

In fact, I'm really not sure how on earth you were thinking that you would be able to get the cable to 'turn that corner' without cutting an access hole there - how were you thinking of trying to do it?

Kind Regards, John

 

[Jupiter01]

As has been said, you mustn't have a diagonal cable run.

This wasn’t going to be intentional. I just think that without clipping it at the turn, the slack cable won’t be in straight lines. Won’t be completely diagonal either but I’m sure you get my point.

In fact, I'm really not sure how on earth you were thinking that you would be able to get the cable to 'turn that corner' without cutting an access hole there - how were you thinking of trying to do it?

Good question!
When I started out with this question, I thought I had to have “something” (may be a blanking plate) at the turning point and hence this will facilitate the straight runs.