AC Voltage Wire Detectors - A Case for the X-Files?

[meditatinghamster]

Hi, at the risk of sounding like a complete loon......

Went to fit a curtain pole up so we can have a curtain in front of the kitchen door.
Used a voltage tester to detect any live wires behind where I need to drill and the detector gave a periodic beep on one side of where I want to drill, but not the other. Fine so there must be voltage behind it. It certainly isn't metal only that's being detected because that would give a continuous tone.

Now comes the weird bit. Looking to see if I could find a better place to drill I scanned other areas, and voltage was being detected was being detected. There appeared to be more areas where voltage was being detected than not, to the point where I thought it must be broken. I found that one half of the living room (which is adjacent to the kitchen) did the same everywhere, but the other side of the living room (facing the front of the house) there was no voltage detected except where you would expect it, i.e around plug sockets and light switches.

Even weirder is that we have antique pine style internal doors, that when I sweep the voltage detecter around it, parts of the door are detected as having voltage, but just random areas of the door, it differs from door to door in the house. Even my pine dressing table gets detected as having voltage.

I've tried with a basic cheapo Wilkos tester that does metal and voltage for £14, and also a £40 Stanley that does voltage and various metals. The result is exactly the same for both.

I've got (what I believe) is a decent grasp of physics and assume that some kind of electromagnetic field gets generated by AC, enough to be detected. Either that or the detector generates an EM field and the AC interferes with it.

I'm sorry if this is the stupidest question asked on this forum, but can anyone tell me what on earth is going on here, as it's driving me crazy. Thank you BTW for having the patience to read my small essay.

 

[hairyben]

I've used a range of "detection" equipment, from those £10 triangle 3-in-1 stud/metal/voltage units, so called "better" versions like stanley intellisense, my £400 cable tracing kit, and £1000 odd quid CAT units.

They all have the same flaw; they take experience to understand and use, and evan then will often only give hints and clues, and sometimes make no freaking sense at all.

If in doubt, you can't beat the good ole quarter inch cold chisel to carefully knock a little bit of plaster off and check- after 10mm or so you'll hit brick/block then it's hammerdrill time.

 

[meditatinghamster]

Thanks for your reply,

Do you know what would cause wood to be detected as voltage?

Everywhere in the house was plasterboarded by the previous owners so I suspect that some kind of foil backing on the plasterboard might be causing the issue. I've just had a thought, if you have a live wire with foil backed plasterboard in front of it, would the foil act as a kind of antenna to the em field generated by the live wire? This would explain why there are wide areas being picked up as being AC?

Placed a piece of 2ft by 2ft tin foil against the wall above a light switch and this actually blocked the detector from picking any voltage up, so I would have thought the foil theory is wrong, unless there's some live wire touching the back of the foil backed plasterboard . As for voltage in the doors being detected, perhaps MI5 have planted high voltage eaves dropping bugs in the doors

 

[mattylad]

Do you by chance live near/under power lines?

 

[meditatinghamster]

Hi Mattylad,

No, nowhere near power lines. Found this post though which is weird and might support the foil backed plasterboard theory though. It certainly made me think twice about chrome light switches as this is something I'd planned to do at some point!

//www.diynot.com/forums/posting.php?mode=reply&t=120393

p.s the link above is worth looking at if only for the funny final post.

 

[hairyben]

I dunno how possible it is for AC to be induced into foil back p'board, which is aluminum(?), but it could act as an antenna of sorts which could lead to weird results.

Like I say detectors are an inexact science- often they need setting for each use, which is itself impossible when you don't know the makeup of what you're detecting. some digging with a screwdriver is often a better way to prove the area before you drill, if you're not in line with a electrical accessory it's unlikely (but not impossible!) there's anything there.

the man who invents x-ray specs will make a killin'.

 

[meditatinghamster]

thanks hairyben,

The next time anything like this comes up I'll use the screwdriver method if I don't trust the detector. As the kitchen door has a small window next to it my wife came up with the idea of using a longer curtain pole that will hold both a short curtain for the window, and a longer one for the door, thus avoiding the 'suspect area' altogether.

We've only been in the house 4 months, and it's our first house so my electrical/building/plumbing knowledge is next to zero! Very grateful for this site and folks like yourself, and I hope to be able to give as much as I get from this site.

 

[ccrowe]

We've only been in the house 4 months, and it's our first house so my electrical/building/plumbing knowledge is next to zero!

In that case, be very careful where you stick your drill. There are areas known as "safe zones", which not everyone knows about, that are areas where electrical cables can be run. These are within a horizontal line 150mm down from the ceiling all around each room, 150mm out from each wall corner, and the lines directly vertical and horizontal from any electrical accessory.

Put your drill or a screw in these areas and you run a risk of hitting a cable.

 

[meditatinghamster]

Hi ccrowe,

Thanks for the tip. Just out of interest does that rule tend to apply for new builds? Ours is about 85 years old and is an end terrace. I believe the previous owners had alot of the electrics redone in the house in the past 7 years though.

They plaster boarded all but two walls in the whole house apparently. It looks great but leaves the obvious question of what the hell is behind it all. Looks like the voltage detectors are poor for precision or guarentee as hairyben says.

I'm surprised there isn't some form of ultrasound device with a small screen that would allow you to "see" partly into walls. Maybe I watch too much sci-fi!