DIY Doctor

Do you Need a Multi Meter When Doing Electrics?

Postby Mr White » Fri Nov 10, 2017 8:12 am

When carrying out D.I.Y. you know that you will need some basic hand tools, hammer, screwdrivers, pliers, saw, cutters. You know this because with out tools you can not carry out the task. So why is it that when carrying out electrical work people often forget about the most important thing..........a multi meter.

If you are changing like for like (say a simple on / off light switch) you can take a picture (always a good idea) of where the wires go on the old switch so you know where to connect them on the new switch.

But take something like a ceiling rose, in the UK a ceiling rose can have 3 cables, each cable having 3 wires (Yes, 9 wires in total)
For arguments sake you have taken down the ceiling rose and now you have 9 wires and which goes where? The bad news is there is NOT a 100% answer to this question (As in the first one goes here, the second one goes there etc...)

I can tell you that one cable goes to the switch, one cable is the incoming supply, and the last cable is the cable to the next light, so now its not looking so bad, but you still don't know which cable does which function, this is where a multi-meter becomes a must as you can use it to "test" each cable to find what it does.

Also you can use a multi-meter for a variety of other things such as checking batteries, fuses, lamps (That's why its called a Multi-meter because it has multiple options and it can be used to do multiple things.

The "odd" thing is you can get a multimeter from less than £10 to £1,000+ but for D.I.Y. one around £10 will suffice.

So I have to say, you have all the screwdrivers, you even have 2 saws, and maybe some bigger hand tools, but why haven't you got a Multi-meter?
Mr White
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Simply Build It

Postby ericmark » Fri Nov 10, 2017 12:35 pm

1) A multi-meter has a battery and a switch, both can cause the meter not to work, so when checking for dead you want a device which can't be switched to wrong scale or have a discharged battery, OK you should use a proving unit, and the proving unit should start at 50 volts AC no point testing the volt meter at 500 volt it may work with that voltage but not at 50 volt so either stepping or at 50 volt. However you still want a tester which can't be switched off.
2) A standard multi-meter can be switched onto amps which will cause a direct short which in turn could cause ionisation of the atmosphere (big bang) so if you are going to use a multi-meter it should be a clamp-on type, one as you can't have a direct short and two because you should test neutrals before you disconnect to ensure no current and you don't have a borrowed neutral, a neon screwdriver is also a good idea to identify a borrowed neutral.
3) Other than the clamp-on ammeter what a multi-meter does it not what is required. You need to measure earth loop impedance, prospective short circuit current, low ohms with at least 250 mA flowing, insulation using at least 250 volt in the main 500 volt, tripping time in milliseconds of the RCD non which can be measured using a multi-meter.

So bare bones testing would need.
1) Volt indicator two wire no battery and no switches.
2) Socket tester with loop like the EZ150.
3) Neon screwdriver.

Next is likely the clamp on ammeter if possible able to measure mA so you can detect leakage current which will trip a RCD.

Then likely the low ohm and insulation tester.

Next the loop impedance and prospective short circuit tester.

Next the RCD tester.

And only when you have all that would you consider a multi-meter, and if you have all that likely a bell tester would actually be of more use.

The odd thing is the GS38 test leads will likely cost more than the multi-meter. Guidance Note GS 38 from the Health and Safety Executive is not there for fun, and most the cheap multi-meters only come with leads suitable to be used with voltages below 50 volt AC great for electronics but useless in fact dangerous for use to low voltage (50 ~ 1000 volt AC). So yes meter is cheap but then expect to spend around £30 for the test leads.
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