Bang! Large flash / bang at voltmeter tips.

[Tasty]

Hi all,

Just had quite a fright & must say I'm pretty annoyed with myself.

I've just tested the ends of a wire to check if it was live (using a fluke voltmeter) and had a massive flash and bang at the points of the probes). I'm annoyed because I should have isolated the circuit and terminated the wire in a block rather than testing wire as it was found (it was left as you'd find twin and earth if had just been cut, not stripped).

Could you guys help me with what the bang was so I can learn properly from this mistake? (I'd have said it was the very loose contact I had between probes and wires but I'd appreciate any thoughts and correction on this). The rcd and mcb blew but everything seems ok now. I've isolated the wire at the switched fused spur unit the cable leads to & will fully isolate before terminating the wire properly now.

Thanks in advance,

Stu

 

[Dazza1976]

Yes fully agree Ian, but how else would you go about testing if it is live ?

He used an approved voltage indicator in the first instance, and that is what caused his flash bang !

In the safe isolation procedures, once you have isolated the circuit to be worked on, you need to test it to see if it is dead, if you cant use an approved voltage tester because of the risk of shorting out, and you cant use a volt stick because they arent approved, then What would be the correct procedure to test it safely ?

Lol, this has the makings of one of those great posts that will be argued about for weeks !

 

[rryles]

Exactly the point I was trying to make Dazza.

The situation is a piece of T+E, that has a cut end. You don't know where it is supplied from or of it is already dead. What do you do?

My suggestion, but I'd welcome others thoughts was:

switch off & lock off main switch
Test tails with volt stick to prove it.
Test mystery cable with volt stick, to confirm it is dead (probably).
Test tails with volt stick again to prove it.
Strip cable and terminate into terminal block, being as careful as possible in case it is actually live still.
Switch back on and main switch.
Use approved voltage indicator to check if cable is live and if it is then identify and isolate as per normal safe isolation procedure.

It's not ideal to be using a volt stick, but it's the best I can think of.

By the way - I routinely use a volt stick, but only as a "second opinion", after using an approved voltage indicator and proving unit.

 

[telectrix]

totally agree there. if you can't safely connect an " approved " tester to the conductors, a volt stick (and care ) is the only way.

 

[malcolmsanford]

Good procedure except you should prove the voltstick works first

Welcome to the real world of electricians, there is not one among us that as not had a flash bang or wallop and no matter how it shakes us I bet it will not be the last.

I can see where Ian is coming from, but perhaps the voltstick is the safest way you can deal with this.

Though There are others ways perhaps not so safe ................................

 

[telectrix]

dab it on a known earth. not only will that show that it'e live, also doubles as a fuse finder.

 

[RogertheBodger]

In extreme cases snip a bit off the end, Carry an old pair of insulated pliers for this reason, don,t forget to avert eyes!

 

[telectrix]

In extreme cases snip a bit off the end, Carry an old pair of insulated pliers for this reason, don,t forget to avert eyes!

don't be a wimp. strip it with your teeth.

 

[RogertheBodger]

don't be a wimp. strip it with your teeth.

Ouch, what a mental picture that is......

 

[Lofty]

I actuallay saw someone do that with a piece of 2 core flex when I was an apprentice. It was the 'norm' for this guy to strip the tails with his teeth only this time he did it on the 'load; end of the mains flex which was still plugged in. it was in a workshop, on the bench and all supplies were from an isolating tx. But it still carbonated ?? the inside of his mouth and funnily enough it was the last time he did it. The guy by the way had been in the trade at that point for over 20 years, with that sort of practice I'm surprised that he managed that long !!.

Cheers,
Lofty.

 

[Marvo]

......in future to isolate all the power if necessary, strip the cable back and put it in a connector block so you can then identify the circuit.........

.......Just to add though, someone mentioned about stripping back the cable and putting in a connector block before testing to see if its live or not, but you wouldnt want to go stripping back cable and terminating until you know that it is dead,.......use a volt stick ?.......

It was probably me that started the minor 'voltstick' riot but I did say 'isolate all the power if necessary' before you strip back the cable to put it in a con block.

I wouldn't bother with the voltstick if the CU was isolated I would just use old sidecutters and 1KV rated insulated gloves and goggles. There's also a little trick you can use with flat twin type cables where you make a very short cut into each side of the cable about an inch along from each other. You cut deep enough to nick the conductors which will then break by gently bending the cable side to side. Once broken you can pull the insulation a little and expose the earth enough to cut it. It's also best to do a few practice runs first on scrap cable and also use old side-cutters, gloves and glasses and I would only do it with smaller cables such as lighting circuits.

 

[ian.settle1]

don't be a wimp. strip it with your teeth.

Who do you think he is Jaws from the Bond movies

 

[RogertheBodger]

Who do you think he is Jaws from the Bond movies

I ust ied i an i urks!

 

[nickblake]

Im going to be realy sarky now .... at the begining of the thread it was asked what was it that caused the bang and Flash ,, Electricity should have been the answer ........ sorry guys couldnt resist that one , looking at the posts its a difficult one this one alot of guys would used a volt stick to check , but ill be honest if this cable is an old unused cable and its grouped with other live cables then the volt stick could operate making it look live when its not ,so the real way too test if its live would be . turn off the supply , connect a junction box that has been tempuarly fixed turn the power back on using a set of voltage test prods test the circuit in question that is after of course you have proved the tester works with a proving unit , long winded way of testing but the safest i can come up with

 

[grantr37]

a meter set on amps or with the probe leads in the wrong meter terminals will blow the leads and cook the meter as well....bet the tips of the probes got blown off...seen it happen before... at least it wasnt your hands that got it just some easily replaced leads/meter...maybe you can buy a Fluke Volt alert pen (1AC or 2AC model) when you replace your tester/leads.....think they are about 20 pounds........I find mine handy

welcome to the Electricians Forum

 

[Knobhead]

To strip a live cable back is simple but needs extreme care.
Make a breach joint PVC to paper-lead live is fun. The instructor’s comment during my LV training “you need a bloody light bulb on your head!” all the LV training was done “live” I can now joint up to 33KV paper-lead you can f**k off if you think I’m doing that live!
If you have any doubts about a cable a 1” plastic handled chisel with a good wooden handled hammer usually sorts them out. Plus gloves and goggles I can be a rough arsed ******* at times, but I’m still alive!
My favourite is an explosive cable spike! Three of us had arc eye & minor burns after picking the wrong 11KV cable. Our own stupid fault, the spike had a remote fire pin but non of us had a piece of string!