How can I tell if these light switch wires are live

FrankFalcon

This is going to sound silly to some people but taking into account that we're talking live electricity I thought it better to check.  I have always head a fear of live electrics which has led to me never really getting involved with lighting etc which some would say this is strange seem as I have no problem repairing PC's and various electrical items (that are not double insulated etc).  Recently, I was reading my copy of Which? magazine and in the article it was suggesting that if domestic appliances were easy for consumers to repair themselves (and where safe) they should try and repair them to save buying a new item, thus not sending the offending item to landfill.  So, in the house we have recently moved into there are some horrendous wall lights outside.  I want to change them but it's fair to say that the previous owner of the house was the opposite of me (when it comes to fiddling with electricity) and although there are 5 lights, of which 3 work, they are operated from 2 different internal wall switches.  Rather than get a sparky in I really want to change these lights myself but I am worried about the wires being live.  I hope you wont mind me asking a couple of questions that (in one case) may seem obvious?

1. If I have a 240v ceiling light bulb that is illuminated and I turn it off at the wall switch does this mean that the wire to this light is 100% not live?  Ie...Can I stick a small electrical screwdriver in the terminal and undo it?  Why would I ask this when surely there's no live to the light because the bulb went out when I flicked the switch?  Well, years ago I heard the term 'permanent live' and it sort of stuck in my head.  So, in this situation...Flick wall switch up -Light illuminates.  Flick it down and light goes out  Is there any way the wire to that light can be live?  Sorry if this sounds obvious.

2. So, taking into account the previous question I know some might suggest to buy a circuit tester and I have no problem in buying the best/most safe circuit tester there is.  However, logic tells me that If I have in front of me a circuit tester and I stick a small metal prong in the live terminal I'm going to get a shock.  Surely, that bit of plastic/rubber insulation on the circuit tester prong is not adequate to give me a shock...Or is it?
I'd love to be confident enough to use a 240V circuit tester to change these lights and hopefully do other jobs.
Cheers

Laz123

I don't know 100% but whenever I have to do anything to do with electrics I simply turn off the switch relating to that particular circuit.

Neil_Jones

If in doubt, turn it off.  If really in doubt, flip the master switch so everything goes off.  Might be overkill but...

RumRat

Always turn it off at the Consumer Unit. Leave the light on and you will be sure that you've turned of the correct circuit when it goes off. If you have an old fashioned fuse box, just pull the fuses or turn off the lot.

pramsay13

Yes it's possible that there is a permanent live to light fittings so never assume just because the light goes out that there is no electricity. 

I normally put on the light, then trip the switch. Once the light is off I will test for dead, even testing the earth and neutral wires to make sure. 

The high resistance in the circuit testers mean you won't get a shock so buy a decent one and use it with confidence. .

Do you have a relative that can help you the first time so you can watch and get pointers?

Farway

RumRat said:

Always turn it off at the Consumer Unit. Leave the light on and you will be sure that you've turned of the correct circuit when it goes off. If you have an old fashioned fuse box, just pull the fuses or turn off the lot.

This ^^^^^, make sure you leave a light on first then you can be sure the circuit is dead once you have turned off at the consumer unit, maybe over kill but rather that than you surely?

One more tip, buy some chocolate blocks terminal strips so if you get messed up or whatever there is a plan B to reconnect wires using the blocks

And take a photo before you disconnect anything, one day you'll be glad you did

chrisw

The light switch 'usually' interrupts the live supply so the bulb holder would be dead. However, if someone has mixed up the live and neutral wires, the light will still appear to work fine but the bulb holder would still be live when turned off.

Switch off at the consumer unit and get a circuit tester to double check.

bellaboo86

There a little gadget you can buy to test if the wire is live.m- my dad has one. Not sure what they’re called though. 

alanwsg

bellaboo86 said:

There a little gadget you can buy to test if the wire is live.m- my dad has one. Not sure what they’re called though. 

These things?
https://www.amazon.co.uk/dp/B000QF5Q4Y

neilmcl

alanwsg said:

bellaboo86 said:

There a little gadget you can buy to test if the wire is live.m- my dad has one. Not sure what they’re called though. 

These things?
https://www.amazon.co.uk/dp/B000QF5Q4Y

The voltage tester pens are better. https://www.screwfix.com/p/lap-ac-non-contact-voltage-detector-pen-1000v-ac/3222g

forgotmyname

neilmcl said:

alanwsg said:

bellaboo86 said:

There a little gadget you can buy to test if the wire is live.m- my dad has one. Not sure what they’re called though. 

These things?
https://www.amazon.co.uk/dp/B000QF5Q4Y

The voltage tester pens are better. https://www.screwfix.com/p/lap-ac-non-contact-voltage-detector-pen-1000v-ac/3222g

NO and NO, neither of those can be trusted in all cases.  Its possible for there to be power and those devices

fail to detect it.

JW actually calls the one in Alans link as dangerous.  The 2nd one should only be used to test that power is on

and not to test that its off.  There can be 240v mains and it will not light up.