Electrical fault finding

[JohnKay]

I often come across cases of someone trying to trace a fault on a live supply using a neon screwdriver, or a cheap multimeter. The dangers may not be obvious. Neon screwdrivers tend to be open to abuse, and can easily be damaged, there's only a tiny resistor between you and 230 volts .

 

In my opinion Most multimeters available in DIY stores are of very poor quality, with leads and probes that are just not up to the job. Great for testing batteries or light bulbs, or on the car, but at 230 volts - not so safe. I've seen one recently that had brittle plastic handles on the probes, if they had been cracked in any way, that meter could be lethal.

 

If you buy a meter, please don't go for a cheapie. you get what you pay for !  For DIY use some of the meters by Rapitest are not too bad, remember it's the leads that you have to handle, and if you put them across 230 volts holding one in each hand, a faulty lead is the last thing you need.With professional meters, the leads have to comply with very strict standards, not so with those on the DIY market, so take care.

 

One very important point when using a meter is if there is a fault on the neutral, (and that's just as likely as on the line) the meter will show zero volts, but the circuit could still be at 230 volts, again take care.

 

 

The one thing I would recommend, is a Volt Stick, Pocket Voltage Indicator, or what ever they get called, is a safe way of testing as there is no contact with the conductor. If you've not come across one, take a look at something like catalogue no. 53855 on the Screwfix site. These are available in most electrical outlets. Once you've used one, the neon screwdriver could end up in the bin !  

 

Lastly, please try not to live test if at all possible, and think before you touch anything. 

Edited April 24, 2013 by JohnKay

[Rich]

Hiya John

 

Some excellent advice there mate... Nice one...

Seriously though, do people actually really try to test their own live house wiring?

 

I wouldn't dare touch mine... My knowledge of 230v electricals stops at putting the plug in the socket... Past the socket is past me..

[JohnKay]

Nice to hear from you Rich.

 

Yes, people do, it's one of the most common queries on other sites. It often goes like "I've tried to replace the hall light fitting, I've taken off the ceiling rose, and now there's seven wires coming out, there's three red, and four blacks. I get 230 volts on one red, and nothing on" etc.

 

This also crops up with heating control circuits, thermostats, motorised valves, and programmers. Out comes the screwdriver, and we have a dangerous situation.

I spent many years fault finding, and I admit most of it was done live, it's quick and easy, but only if you know what you are doing !

 

There's other problems that, with using a meter cause problems. It's easy for someone to think that they can be used to test for safety - they can't, the meter for that is a very accurate instrument with a price tag to match. 

 

Dealing with AC is another problem, people expect it to behave in exactly the same way as DC - it doesn't, and there's many cases where a meter can cause confusion.

 

So, anyone intending any electrical work, please do your homework first. Take your time, think before doing anything, and make absolutely sure you are safe.

SWITCH OFF FIRST. 

 

This is a nice site Rich, hope to see a bit more action soon.

[Rich]

Thanks John...

I hope to see more action here soon too :-)

 

Know what you mean about meters though, I'm melted a fair few sets of cables on meters just messing about with low voltage DC stuff with my model airplanes and lithium Polymer batteries..

 

It stops being funny when you short circuit a 150amp battery pack the size of an old nokia phone..