Cables routed in cavity walls?

[amfisted]

After 36 years of living in draughty Victorian houses with solid brickwork, my wife and I have graduated at last to a property which has cavity walls.

Simple question: what, if any, is the likelihood that cables have been routed within cavities rather than buried in the plasterwork? The place was built in 1973 and has solid concrete floors. I intend to hang pictures, but for the time being and until I can get hold of a decent cable locator, I'm avoiding any area which is above an existing socket.

Thank you.

 

[sparkwright]

Houses built in the 40s, 50s and 60s were very often built with cables in cavities.

By the 70s it was more common to use PVC oval conduit nailed to the wall before plastering.

But who knows for sure what you have?

Even a house built with PVC oval conduit could have had additions done down the cavity.

If you are comfortable, with all the power off, you could loosen some faceplates to see where the wiring goes. This may give you some indication, but remember that just because a cable appears to go in a particular direction, it doesn't mean it actually does.

 

[conny]

Play safe and get a cable locator but you should always use the rule of thumb that even if cable is in conduit/trunking it is still unwise to nail/screw in line with the vertical or horizontal of an outlet.

As for the possibility of the cables being run in the cavity, then yes, there is that possibility though they are not supposed to be. Having said that, my last house was rewired by the previous owner, (had certs etc on completion of sale), yet when I was decorating I took a few socket faces off and discovered the cables brought through a hole in the inner brickwork. When I climbed into the loft I discovered the lighting cables and shower cable had been brought up through the cavity as well.

 

[amfisted]

Thanks very much.

I'll wait until I have a reliable cable locator before hanging anything else; unless any of the locations chosen by the previous owners prove to be suitable.

Could someone recommend a cable locator, please? I did buy a DIY model but to be frank and as referred to before, it was worse than useless.

 

[JohnW2]

Simple question: what, if any, is the likelihood that cables have been routed within cavities rather than buried in the plasterwork? The place was built in 1973 and has solid concrete floors. I intend to hang pictures, but for the time being and until I can get hold of a decent cable locator, I'm avoiding any area which is above an existing socket.

I'm not sure I fully understand the reasoning behind your question. Even if some of the cables in your house are within cavities (which, as has been said, is not impossible), it would still be very possible (probable) that there would also be some cables only buried in plaster. You will therefore always have to assume the possibility of there being potentially vulnerable cables in plaster (hopefully in the defined 'safe zones', vertically or horizontally aligned to sockets, switches etc.) - and either avoid putting nails/screws into such places or get as good a cable locator as you can (none are by any means perfect) and hope that enables you to avoid any disasters.

One can obviously have more confidence in a cable locator when it does detect a cable than when it doesn't - so, if it fails to find a cable coming from, say, a socket in the region which interests you, it adds a bit of reassurance if the device is able to detect cable(s) going from the socket (or whatever) in other directions. Of course, one can never be certain of how many cables there may be, possibly going in different directions!

Kind Regards, John

 

[amfisted]

The question was partly inspired by simple curiosity, John, with more than a tinge of pragmatism. Until July we had always occupied houses with solid walls, where cables tended to be buried in plaster, and I just wondered how different things were likely to be in a more modern property, and how one should approach the matter of attaching things to cavity walls without tripping any RCDs. I understand that even if mainly routed within cavities there is still likely to be some cabling on the inside surface of the walls, but simply wondered about the extent to which that was likely to be the case. I suppose the safest approach is, as usual, "assume the worst".

Interesting that you say cable locators are by no means perfect. Strikes me that anything less than reliable operation by such a device renders it useless. Do electricians make much, if any use of them?

One lesson I've learned from this thread is that the picture hooks with shorter pins which the previous owner had used, and which I quickly discarded were not, perhaps, as worthless as I initially thought they were.

 

[JohnW2]

The question was partly inspired by simple curiosity, John, with more than a tinge of pragmatism. Until July we had always occupied houses with solid walls, where cables tended to be buried in plaster, and I just wondered how different things were likely to be in a more modern property, and how one should approach the matter of attaching things to cavity walls without tripping any RCDs. I understand that even if mainly routed within cavities there is still likely to be some cabling on the inside surface of the walls, but simply wondered about the extent to which that was likely to be the case. I suppose the safest approach is, as usual, "assume the worst".

Quite. You really don't have any option but to "assume the worst". Even if you knew for certain that the vast majority of the cables were in cavities, you could never be certain that there were none buried in plaster.

Interesting that you say cable locators are by no means perfect. Strikes me that anything less than reliable operation by such a device renders it useless. Do electricians make much, if any use of them?

It's not really electricians. It's the plumbers, carpenters, decorators and DIYers etc. who are at risk of putting drills/screws.nails/whatever through cables buried (by electricians) in plaster. Even good detectors are by no means 100% effective - so you can never totally rely on them. However, as I said, if one can do it by means of 'positive', rather than 'negative' findings, that is much more reassuring. If you look inside, say, a switch or socket, and see that there are, two, cables entering it, if your device is able to detect where those two cables do go, then that is pretty strong (albeit not totally certain) evidence that there aren't cables going in any other directions from the switch/socket.

One lesson I've learned from this thread is that the picture hooks with shorter pins which the previous owner had used, and which I quickly discarded were not, perhaps, as worthless as I initially thought they were.

Perhaps, but there are no rules/laws about how shallow a cable may be buried in plaster, so even short pins might hit a cable!

Kind Regards, John

 

[amfisted]

Thanks again for your help.

I'll think VERY hard about locating stuff on these particular walls, and may ultimately decide that the "minimalist, non-electrocuted" look is best after all. I reckon I can fit most of those pictures and things in the loft...

 

[conny]

Even under 'old' regulations cables buried in plaster are advised to have been capped. Using the picture hooks with short pins, (about 4-5mm long), should not penetrate a cable buried unless it is really close to the surface. I have found when cables are buried this shallow the plaster tends to flake away as it is so thin, so the chances of hitting a buried cable with these hooks appears to be very slim indeed.

(And despite their small size they are surprisingly strong! )

 

[amfisted]

I actually used an existing one to hang a rather heavy ornate plate, thinking the pins went much deeper; and was dismayed to find just how shallow they are when I took them down prior to decorating.

I suppose if the plaster is sound they're good enough for moderately heavy stuff, as long as out of reach of kids. They are pre-angled downwards, which helps.

 

[JohnW2]

Thanks again for your help. I'll think VERY hard about locating stuff on these particular walls, and may ultimately decide that the "minimalist, non-electrocuted" look is best after all. I reckon I can fit most of those pictures and things in the loft...

I think it's easy to get too paranoid about all this. It's often possible to be pretty sure that there's no logical reason for their to be cables in a particular bit of wall, which makes it very unlikley (but not impossible!) that there are any. If, for example, there are lowish sockets that you know (by cable detector or otherwise) are fed from below, and if there is nothing electrical on the wall above the socket, then the chances of there being a cable up there are very small. If you couple that with the use of a good cable detector, the chances of you experiencing any problems are even smaller.

Kind Regards, John

 

[amfisted]

Thanks again.

I suppose the best approach in this scenario, as with many others, is "expect the worst, but employ common sense to make the best more likely".

 

[ban-all-sheds]

Bosch DMF or GMS detectors are likely to be the best, short of spending several £hundreds on something really sophisticated. Certainly way better than any cheap DIY tat.

An excellent rule of thumb is that Bosch tools in the colour which has the same first letter as their company name are good, those in another colour not so good.

 

[JohnW2]

Thanks again. I suppose the best approach in this scenario, as with many others, is "expect the worst, but employ common sense to make the best more likely".

Quite so - that's why we should attempt to drive as safely as possible, even though we have put on our seat belt and are driving a car with air bags. Part of the 'common sense' obviously includes acknowledgement of the fact that we can't (shouldn't!) live our lives cocooned in a padded cell!

Kind Regards, John