using multimeter

[DrGonzo]

Anyone know some useful guides for using as multimeter?

On the back of a recent post where I have connected a new light with metal fixture I want to:
(a) do a ground test &
(b) check that the metal fixture is not live (so basically use it as a voltage tester instead of those neon screwdriver type things).

ANy ideas on how to go about this?

 

[breezer]

as i said bury the meter first then read the instructions.

its amazing what uses you will find for it

 

[DrGonzo]

The instructions aren't that detailed so I'm trying to find some internet guides although none of them seem that good either.

Just wondering if there are any recommended ones.

 

[breezer]

well, seeing as you have the instructions and i dont what do they say?

although the principals are the same the knobs and swiches are differnt, but the symbols must be the same.

eg, there are auto ranging, ones with one dial, some with sliders

 

[DrGonzo]

Well it has a switch to select DC voltage, AC voltage, current, or resistance and then the dial has the relevant maximum settings, e.g. 200 V, 20 V, 2 V, etc.

The instructions have a basic guide for how to get each of these measurements, except I'm not quite sure how you could test whether a screw, metal fitting, wire, etc. was live without getting the black test lead into the circuit?
For example, a neon tester relies on you connecting the circuit to yourself to test whether it might be live. How do you do the same with a multimeter? I would touch the metal casing and then connect the other end to a known earth (not myself obviosuly). What can I use as the known earth?

 

[breezer]

What can I use as the known earth?

the earth "socket" on a normal socket, (the top one) or its screws

if you want to be extravagant you can buy an earth plug, its what pc builders use to connect an earth wrist band to to prvent static build up

 

[DrGonzo]

That assumes the earth socket is earthed properly?

Yeah, typically the wires on the multimeter aren't long enough to go from the ceiling light to the nearest earth wall socket. Any ideas?
Can I make some sort of weird plug extension, which has a plug on 2 ends only connected by the earths, plug that in the wall, and then touch the black lead onto the top of the metal earth pin ?

 

[breezer]

Can I make some sort of weird plug extension, which has a plug on 2 ends only connected by the earths, plug that in the wall, and then touch the black lead onto the top of the metal earth pin ?

why two plugs? thats making life difficult

 

[DrGonzo]

Just thought it would be safer than having a wire hanging about randomly.
But in theory, it would work?
Now, if the metal casing was in fact live, wouldn't this trip the fuse box immediately, via the new earth route to the socket?

Secondly, how do you do a ground test to test that the metal is grounded properly...or in fact that any socket in the house is grounded properly?

Thanks.

 

[dingbat]

DG, whilst your intentions are honourable I doubt your ability to test safely. However, rather than let you electrocute yourself, do this:

Switch off your entire installation at the consumer unit then carefully remove the front.
Connect a length of cable (any old length of cable will do) to the earth bar in the consumer unit and take the other end to the fitting you want to test.
Set your meter on 'continuity', selecting a low ohms range if available and measure between the exposed metallic casing of the light and the end of the cable. If you get a reading then your exposed metalwork is earthed.
To get a value for the resistance of the protective conductor path you need to subtract the resistance of the cable you used. (You need to have a value of less than 1.3 ohms for a 6A circuit breaker [Table 41C, BS 7671 x 80%])

If this test works out okay you have no need to test for live - I would not want to advise you on testing live circuits - you have already proved that the circuit protective conductor is continuous back to the consumer unit.

If this test shows an open circuit I really think you need to call in an electrician to do it all properly.

I hope that helps.

 

[Dippy]

I've got to agree. If you don't know how to use a multimeter then you really shouldn't be doing your own electrics.

 

[DrGonzo]

That's fair enough but I was just interested in a way of using it like a neon tester out of interest.

For example, what do people do if they don't have a neon tester but want to test a socket etc. before unscrewing something. There must be a standard way to do this with a multimeter considering the amount of times neon testers have been abused on this forum.

I realise that a neon tester might not be as reliable but if you have to start dragging about earthing wires etc. just to use your multimeter for the same thing, then it just doesn't seem as easy !

 

[breezer]

life isnt easy.

and no resonable electrician would use a neon tester screwdriver. they are unreliable, and give false readings.

why dont you buy some 6v lamps, lamp holder etc and "play" with them and see what your meter is capable of.

I understand your concern regarding your new lights, but to be honest i do think you are a bit out of your depth.

as i said earlier, its amazing what safe uses you can find for a multi meter.

using battery operated kit is safe.

if its of any use its how i started.

 

[Spark123]

(You need to have a value of less than 1.3 ohms for a 6A circuit breaker [Table 41C, BS 7671 x 80%])

I think this table is part of regulation 413-02-12 where you can increase the disconnection time for a portable appliance / socket outlet from 0.4s to 5s if you limit the voltage between appliance and MET, 50v rule?