Jb
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Is there an electrician in the house?OK So today's jobs included putting up shelving in an alcove next to a chimney. Easy enough but before I do it I do my usual better safe than sorry check to see if there are any cables around the place with one of those cable detectors that buzzes whenever you wave it over a mains cable.
Two of the alcove walls come up clean but the entirety of the chimney wall reads as though there are cables buried in it which seems unlikely. So I go up into the loft to see if there are any obvious cables going down by the side of the chimney which there are not. While there I tried the cable detector against the chimney and again it reads as having cables buried in it. This is immediately below the roof line and the only thing above that is one TV aerial.
What is this thing detecting? Is it really mains? Can I put off putting up these shelves?, is something awry with the wiring in my house?
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Jonnyboy
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Could it be that your chimney is lined? I'm not 100% sure by I think that cable detectors pick up both live and dead electricity cables.
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Treacodactyl
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I'm not an electrician but I have a cheap cable detector that often gets confused by damp. Not damp you should worry about but enough to make it rather useless at detecting cables in some walls. It might be that.
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Gervase
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Most cable/stud detectors are bloody useless. It's probably picking up your steel flue liner, or possibly even some high-alumina cement used to backfll the flue if you've got a ceramic liner.
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Jb
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So I guess a more reliable cable detector is to drill regardless and listen out for the screams? 
I'm honestly not sure if the chimney is lined or not (we only moved in a few weeks ago). It is an ex council house so the construction is belt and braces on everything. So if there was ever any advantage to having it lined then it probably is.
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Jonnyboy
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| Gervase wrote: | | Most cable/stud detectors are bloody useless. It's probably picking up your steel flue liner, or possibly even some high-alumina cement used to backfll the flue if you've got a ceramic liner. |
My God, I was on to something.
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Jb
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I thought cable detectors only detected live cables? I just tried my cable with an extension lead. Detector next to extension lead and it buzzes away, turn off anything plugged into the extension and it still buzzes, unplug the extension and it stops. Which suggests that it detects live circuits rather than just the metal in a cable.
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Jonnyboy
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Turn your supply off and see if it buzzes at the chimney then.
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sean
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No reply. Which bit of advice was duff then?
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sean
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| JB wrote: | | So I guess a more reliable cable detector is to drill regardless and listen out for the screams? |
If your wiring's properly earthed and has decent fuses etc it just makes your jaw snap closed anyway, not really painful or anything.
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Jb
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| sean wrote: | | No reply. Which bit of advice was duff then? |
Still here 
In fact I was just about to start on the shelves. I'm confident there's nothing behind the wall because I've found where the lighting cables run and I would expect unless something very bizarre is going on that the power cables run through the floor and only up as far as the sockets.
I was about to shut down the electricity and retest as Jonnyboy suggested but I came here to procastinate first while Mrs JB was was window shopping for lights.
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pricey
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Sorry only just seen this. As long as there are no Switches or Sockets above or below where you are going to drill then there shouldn't be any cables there, 99.9%. But you do have DIYers that run cables horizontally  , but don't worry it will only make a mess of the drill bit if you do hit any thing, if you feel you are drilling into plastic or metal then stop.
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Jb
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| pricey wrote: | | Sorry only just seen this. As long as there are no Switches or Sockets above or below where you are going to drill then there shouldn't be any cables there, 99.9%. But you do have DIYers that run cables horizontally , but don't worry it will only make a mess of the drill bit if you do hit any thing, if you feel you are drilling into plastic or metal then stop. |
At the house we've just moved from the person before me had decided that cables could run diagonally (not such much as  ). Also they had decided that rather than buy larger junction boxes more cables could be fitted in the existing junction boxes by the simple expedient of omitting the earth cables .
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MarkS
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how about water pipes ? rad pipes often seem to run along chimneys
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