Measuring Mains Voltage - Blown Multimeter ?

[WhatNext]

Hi

I wanted to measure the mains voltage via the power lead that runs to my kettle.

I set the meter to the 250V ac range.

I inserted the black probe all the way into the Earth terminal so that no bare metal on the probe tip was visible, so as to be safe.

When I inserted the red probe into the Live terminal my multimeter gave off a small arc and the RCB tripped ? I removed the probes and reset the RCD without issue - the kettle worked as normal.

When I opened up the rear of the multimeter the circuit card was badly charred and the battery was partially ruptured.

The meter was over 35 years old and I happened to notice that the battery was dated 2006, however it was still working when checking for continuity.

Based on what I have described I think that the multimeter failed which is why the RCB tripped ?

Does this sound plausible ?

Many thanks in advance.

 

[rsgaz]

Sounds like you had the leads in the wrong hole on the meter.

 

[WhatNext]

No I should have said that I also checked that, however I was under the impression when measuring ac that it did not matter, however as I say the black lead went to "-" and the red lead went to "+".

 

[rsgaz]

I was under the impression when measuring ac that it did not matter

No, I don't mean that you had the leads just swapped over.
I meant, does your meter have three or even 4 holes for the two leads to go in?
Had you been measuring amps before switching to volts?

 

[WhatNext]

Hi thanks for your reply. The meter looked very similar to this picture.

No I never use the meter to measure amps.

 

[flameport]

If the leads were correctly connected, then it was set to the wrong function, probably resistance, which would apply the mains voltage across the battery via the internal circuits of the meter.

Pure luck that it didn't cause serious injury or a fire.

 

[WhatNext]

Thanks flameport, but I double checked that it was set to the 250V ac setting before I started to use it.

 

[JohnW2]

If the leads were correctly connected, then it was set to the wrong function, probably resistance, which would apply the mains voltage across the battery via the internal circuits of the meter. ... Pure luck that it didn't cause serious injury or a fire.

IF everything we have been told is correct/true, then I presume the meter must have developed an internal fault - it appears that the meter only had two sockets into which to plug the leads (so not possibility of connecting them incorrectly), and the OP wrote that "I set the meter to the 250V ac range.".

Kind Regards, John

 

[DetlefSchmitz]

1) The picture shown was only 'like' the OP's meter, so may not be identical.
2) It is reasonably easy to switch the wrong end of the switch (the one without the dot) to the required setting without realising.

 

[WhatNext]

Many thanks to everyone - my suspicion was an internal fault in the meter which created a short and tripped the RCD.

 

[JohnW2]

1) The picture shown was only 'like' the OP's meter, so may not be identical. ... 2) It is reasonably easy to switch the wrong end of the switch (the one without the dot) to the required setting without realising.

Yep, all possibilities - hence my "IF".

Kind Regards, John

 

[John D v2.0]

That meter doesn't look good quality enough to measure mains anyway so I'm with JohnW2. Most meters and their leads will be marked CAT III or CAT IV and a voltage which means they are safe for measuring mains supplies

 

[JohnW2]

That meter doesn't look good quality enough to measure mains anyway so I'm with JohnW2. Most meters and their leads will be marked CAT III or CAT IV and a voltage which means they are safe for measuring mains supplies

I wasn't saying anything about the quality of the meter (as designed/manufactured) - but, rather, that (if everything we'd been told was correct) it had quite probably developed an internal fault.

I spent years/decades of my youth using meters like the one illustrated to measure mains (and much higher) voltages, and that was long before any of us had even heard of CAT III/IV (which probably didn't exist back then), and they weren't necessarily of inadequate quality to measure mains voltages (at least by the safety standards of the day) - at the ('good') extreme, my AVO 8 and AVO Multiminor still work fine, and I would have no hesitation to use either to measure mains voltage today.

Kind Regards, John

 

[JohnW2]

.... at the ('good') extreme, my AVO 8 and AVO Multiminor still work fine, and I would have no hesitation to use either to measure mains voltage today.

... and just to prove it (and I'm still alive, despite there not being a CAT III/IV marking in sight!) (I guess I bought this one around 1964/5)...

Kind REWgards, John

 

[Jackrae]

There's no way on earth you can compare a piece of far eastern cr4p with an AVO Multiminor