Live neutral cables??

[Ookysoft]

Hey folks!

I'm trying to wire in a few lights into a friends house. We have found some of the [ apparently] neutral cables to be live. The neon in the electrical screwdriver shows a glow - ableit not as bright as other 'live' cables.

I have 1 light switch which appears to be equally live on both live and neutral [ switched live I assume ] cables - the switch is TOTALY broken apart so the cables are isolated from each other but both make the screwdriver glow!!

Has someone sometime connected a live to a neutral somewhere indicated by this weaker glow? I've tried using the weaker glow as a 'live' to light a lamp but nothing......

Elsewhere in the house, what seems like possible 2 way switching had ALL lives at 1 switch!!

I'm an experienced DIYer when it comes to electrics & plumbing - so this could juct be a simple thing a pro would know.

Your thoughts please?

BoB

 

[ninebob]

Neon screwdrivers are pants, full stop. Renowned for giving false readings. If you're going to be doing any electrical work it is essential that you buy yourself a proper multimeter. Less than a tenner in Argos or wherever. Try again with one of those, and if you really are still measuring a significant voltage, get back to us.

Also, you should be aware that the twin & earth going to most light switches is NOT live and neutral, it is live and switched live. Think about what a light switch actually does: it allows a live current to flow through it when switched on. Neutral is only at the far side of the item being switched.

 

[Ookysoft]

Ooh!

Thank you for a rapid response.

Ok, I have a multimeter.... will come back to friends with it next week....

I have to say, it's the FIRST time this screwdriver has EVER given me a glow off of a neutral cable. I test both as a habit when doing any wireing.

Equally, I have 1 of those current detector gizmo's - I assume works by unduction - so you can tell if a cable is live or not [ finds breaks too ] - it beeps on a light cable when, apparently, switched off...... Again, the FIRST time it's messing with me.

Will use the multimeter & get back.

 

[breezer]

sorry the word is induction, and yes they are none too good either

 

[Damocles]

Any fluorescent light bulbs? They can do funny things.

Any time a disconnected wire is running parallel to a live one it will get some voltage induced on it. Mains is AC so it can pass through either transformers (via its magnetic field) or capacitors (those two copper wires separated by 3mm of pvc dielectric). The available current is very small, but can light a neon. A lightbulb should short it out. Are you quite sure it was neutral and not switched live?

 

[Ookysoft]

There are flourescents running from the same fuse - 2 of these actually have capaciters between live & neutral.

There are 5 cables bunched together in a part of that run. So I guess induced current is probable - especially if it takes very little to spark a neon & as I already suggested the neon is weak on the offending wires.

Nope, not switched lives - though some of this bloody wiring is, quite literally, taped together in places!!

Tell me, if live WERE connected directly to neutral somewhere, wouldn't that just keep blowing the fuses?

Back to the multimeter. What kind of voltage would be 'acceptable' if induced.

 

[Paul_C]

If you're using a modern digital meter you need to be wary of the readings too. These meters generally have a very high input impedance (around 10 megohms), so capacitive coupling can easily give readings of 100V or more on wires which are disconnected at both ends (e.g. a switch return with the switch off and no bulb in the holder).

 

[securespark]

I'm an experienced DIYer when it comes to electrics

Don't be upset by nine's response. After all, you claim the above, but then admit to never having owned a MM - until now!

 

[Panjandrum]

Is there something mystical about owning a multimeter?
I see no conflict in Ookysoft's claim to be an experienced DIYer without a multimeter.
A lot of the inspiration, talent and cunning in DIY is in knowing what you can do, safely and well, within the limitations of the equipment at your disposal.
I don't own a torque wrench, a scaffolding tower, a blowlamp, a cement mixer, or a seemingly endless list of other vital equipment; that doesn't make me incompetent at DIY car jobs, decorating, plumbing or bricklaying.
It restricts the jobs I am prepared to undertake and often adds to the effort and expense of the jobs I do undertake.
PJ

 

[SwindonSpark]

To quote ban-all-sheds:

Do you have screwdrivers for dealing with screws?

A hammer for dealing with nails?

A saw for cutting wood?

Why don't you have a meter?

Panjandrum, why do you think a multi-meter is a "specialist" piece of equipment?
It's as basic and necessary as a screwdriver!

 

[ban-all-sheds]

Is there something mystical about owning a multimeter?

No, but there's a lot daft about not owning one...

I see no conflict in Ookysoft's claim to be an experienced DIYer without a multimeter.

I can. (Or should I say "could", as he does have one) Sure - a person can be experienced and not own one because he'd moved/given up/dropped it down the lav, but an experienced person would go and get one before taking up DIY activities again.

A lot of the inspiration, talent and cunning in DIY is in knowing what you can do, safely and well, within the limitations of the equipment at your disposal.

Agreed - but that does not extend as far as bodging solutions because you don't have the right tool.

I don't own a torque wrench,

Inexcusable if you do DIY mechanics - almost every nut and bolt on a car has a torque setting, and getting it wrong can have fatal results.

a scaffolding tower,

Fair enough - easy to hire and hard to store, and not needed very often.

a blowlamp,

Well - I suppose if you want to use compression fittings everywhere....

a cement mixer,

even more difficult to store. And anyway - people were mixing mortar and cement by hand for quite some time before mixers were invented.

or a seemingly endless list of other vital equipment; that doesn't make me incompetent at DIY car jobs, decorating, plumbing or bricklaying.

It might do - in some cases more than others, as I have observed.

It restricts the jobs I am prepared to undertake and often adds to the effort and expense of the jobs I do undertake.
PJ

You need to be very clear about which tools are essential and which are just time-savers.

A multimeter is essential. An SDS box-sinker or a chasing tool are not.

 

[Panjandrum]

Well I didn't suggest a multimeter was a "specialist" piece of equipment, and I certainly would not want to suggest it wasn't immensely useful.
But - a few observations:
I have been a bit surprised at the criticism that falls on people posting here who mention that they do not have access to a multimeter;
Being without a multimeter is not a fundamental character flaw, and no-one can say that all DIY electrics done without one has been bodged (and of course there are always one or two examples where the experts with the multimeters have been known to slip up a little).
On the other hand, you may have come across more of the DIY disasters than I have
PS: And of course it is possible to get things a little mixed up even if you use a meter - quote from another thread:
"I've now checked for resistance across the solenoid as advised and got a reading of 3.5 with the multimeter on the 200V setting."

 

[Canny]

Have to agree with the experts here, the multimeter is to electrics what a saw is to woodwork. The differences are likely which one is used by which person. I'm sure ban-all-sheds and the other regulars here have much better equipment than my multimeter and socket tester but they were the first items on my shopping list when I decided to put my theory knowledge to practical use.

Sure its possible to manage without them, you could cover a certain amount of its functionality with the right combinations of light bulbs, batteries and additional cables/accessories, but for the sake of 20 quid its not worth the effort of building the appropriate cicuits.

 

[andy]

i have a cheap multimeter and socket tester what stay in my toolcase. they dont get used very often but come in useful for fault finding. to do basic DIY you dont need a £300 multimeter, a £9.99 basic type is enough

 

[swelec]

when clearing out my attic, found my old MK7 avo - if anything dates me, that does I thought

never use it now I have a cheapo digital meter

looked on google - found they are still for sale - new MK7 ( analogue ) at £695 ?????????????

ebay just sold an inferior model for £65

Any offers