what's going on?

[IanJ]

I'm in the process of replacing an outside light - straightforward swap. Nothing wrong with the previous light - just damned ugly

I tested the junction block inside the old fitting before removing it, using a non-contact tester (the type that bleeps if there's a live nearby) and a contact tester (one of those cheap little screwdrivers that lights up in the handle if it touches a live).

With the circuit switched off at the fuse box, obviously nothing at all. But with the circuit switched on but the light switch off, the live connection shows a slight live (the non-contact tester bleeps slightly and the contact tester lights slightly). With the light switch on, the light in the contact tester gets brighter, and the bleep in the non-contact tester gets louder and faster.

That's confusing enough, but I also get the dim light and the slight bleep on the earth connection - although no difference here when the light switch is on or off.

Nothing at all on the neutral - at least that's something
I've left the old light fitting in place for now - it still works fine.

So what's going on? Should I be worried? Should I carry on and replace the light? Or do I need an electrician?
12-year-old house, so all wiring is modern. It's a one-way light-switch for the outside light, although wired in to a two-gang two-way switch that feeds the kitchen light. There's a single switch on the other side of the kitchen that also controls the kitchen light. All lights are working fine.

Any advice appreciated!

 

[breezer]

throw both testers away they are rubbish. That is they are rubbish as testers, but great as entertinment.

the neon sometimes makes a good screwdriver

the non contact tester is good fun if you wear a jumper and rub it up and down your arm fast (try it and see)

 

[IanJ]

Thanks breezer. The neon is a crap screwdriver too, so in the bin they'll both go.
I've just been reading the other thread on this (that'll teach me to scroll down and read first ), so I'm off to buy myself a multi-meter tomorrow. Any recommendations?

 

[breezer]

maplin

 

[andy]

maplin

maplin is always expensive

if you have time to wait for delivers, try www.cpc.co.uk

 

[plugwash]

maplins nice if you want stuff quickly (i would never use them mail order though)

also remember that while the base price on online suppliers may be cheaper you will almost certinaly get stung with a small order charge

 

[Damocles]

To get back to your original post, I would have expected the same result with your contact testers from E as from N. These two wires should be connected by a pretty low resistance of 1 ohm or so. This does suggest you might have a bad earth connection.

As to the live: when the switch is off, the remaining live wiring after the switch may not be connected to anything, so it is floating, so it may indeed float up enough to set off the testers. This is normal with this kind of test equipment. Did you have the lamp and bulb connected when you did this test? As the lamp would tend to connect the live wire to neutral.

 

[IanJ]

Thanks Damocles. I was testing the connections without the old light fitting and bulb connected (and I've since binned it).

Will a multimeter test show up a bad earth connection? If so, what sort of reading should I be looking for?

Underneath my kitchen sink is what looks like the main earth clamp for the house, connected to the copper pipe of the rising main. Looks fine. But just beneath the floor of the cupboard, the copper pipe is connected to a blue plastic water supply pipe. So does that mean there's no connection to earth? Or would Barratt (original builders of the house 12 years ago, bless 'em ) have installed an earth rod somewhere else?

Sorry to sound thick ...

 

[Damocles]

earthing really has to do with connecting the earth wire to the source of the electricity. This is done where the electricity supply comes into your house. By the suppliers fuse and meter should be a big connector block of some sort which all the earth wires go to. Could be an earth rod, but most likely the earth comes from the supply cable.

The pipe connection is not to earth the electrcity, but to join the pipe up to the existing earth system.

multimeter should show oV between N and E or anyway a small reading (if anything is turned on, which on the whole it shold not be if you are poking about with the wires)