Why are proving units so expensive?

[Adam W]

I don't think I would have even considered trying to 'safely isolate' an installation which hadn't had a service head fitted yet.
Although if you did, and tried to prove your instrument on the incoming side of the main switch you might think your meter was broken (had you not tried to prove live first).

 

[Steve_P]

Hey!! I used mine today. More to see if it was working than anything. It was so it went back in the bag.

 

[jaresquire]

Simple answer is because the scams require you to have one,thats why they are so dear.Like the nut I once needed for my van,average price of a nut about 50p this one from dealer was about a tenner,when I kicked off about the price the reply was yeah mate course its dear but you cant drive the van without it!

That must be the nut behind the wheel?

 

[Risteard]

I use a Martindale PD690 all the time. Wouldn't be without it. Can be a lot handier than using a known supply at times.

 

[Guest111]

suprised they haven,t started asking where your spare batteries are when you get inspected,when I was at BT they used to have these auditors popping out to check you had everything,and god help you if you didn,t have spare batteries,sods law said they,d always pop up when you had just put your spare set in one of the testers,even though you had the old set to prove the change they still gave you grief for not having a spare set!

 

[DNS1]

Can I assume that the "auto-test" button on the voltage detector isn't a substitute for the proving unit (in the eyes of the NIC?)

 

[DNS1]

Can probably ignore that last post... I've been reliably informed that all the "test" button does is prove the lights work, not that it can detect anything!

 

[thekingiam]

just thinking about this, unless i am wrong the only thing that could be inside a proving unit is a rechargable battery, a capacitor and female connectors surely you could make your own?

 

[spark 68]

just thinking about this, unless i am wrong the only thing that could be inside a proving unit is a rechargable battery, a capacitor and female connectors surely you could make your own?

There is a bit more to it than that, it consists of a small step up circuit to give out a higher voltage than the battery that powers it, some give out circa 240V, and some like my Martindale PD690 give out nominally above 690 V for proving a VI suitable for 3 phase work.

 

[thekingiam]

ok could someone smash one open so we can see how it ticks! please!!!! post pics as well..

 

[spark 68]

I have two smaller faulty ones that I got given, I may take one of these to bits later and post the pics.

I would rather not take the afore mentioned PD690 one apart.

 

[brman]

as spark68 said you need a step up circuit. This can either be done with a transformer (but you also need to create an AC supply from the battery to supply the tranformer) or a charge pump.

A bit of info here.... Voltage multiplier - Wikipedia, the free encyclopedia



Or of course you could just use the IR test mode on your MFT on the odd occasion when you don't have a live supply to use!

 

[ickleant]

Talking of info:

Why Are Proving Units So Expensive? / Tester Blog

That explains it pretty well but dosen't make my wallet feel any happier!

they seem to have a lot of articles that people have been asking on this forum....

 

[stef]

I have a circuit diagram somewhere, only a few tranny's and a transformer, not much to it. Basically a battery powered oscillator (sine) which transforms up to 240 v. But when you build one yourself you might get problems getting it calibrated.

 

[ickleant]

I vave a corcuit diagram somewhere, only a few tranny's and a transformer, not much to it. Basically a battery powered oscillator (sine) which transforms up to 240 v. But when you build one yourself you might get problems getting it calibrated.

then you just need to build a calibrator

 

[stef]

... Which needs to be calibrated as well. I don't know actually whether a proving unit has to be calibrated at all. If not then yes, you can build one yourself.

 

[1shortcircuit]

I know I will get slapped wrists for this but I have got into the habit of testing for dead with my voltage indicator then double check with my voltage stick(non contact type). At least I can wave my voltage stick around the tails to check it is still working. Something I cannot do with a VI if the isolator/meter is sealed.

I reckon proving units are so expensive purely because they don't sell enough of them to get economies of scale!

That's going to do more than bite you on the arse one day, fine to use to prove live but using it to prove dead could well make you dead :lol Silly sausage

 

[snowhead]

... Which needs to be calibrated as well. I don't know actually whether a proving unit has to be calibrated at all. If not then yes, you can build one yourself.

I've just checked the instructions on my new Martindale.

Proving unit, no mention of calibration.
Voltage indicator, to be calibrated yearly.

 

[madseb]

i got one free as an "incetive"at an old firm. and didnt realy use it. must admit ive allways used the incoming supply as a means of proving my tester.
although after looking at what my little kewtech unit would have cost. cant belive the prices?

 

[IzzyS]

Proving on the incomer is no good when there is no supply on the incomer.

In 45 years I've never felt the need to own or use one, I've always used the 3 meter system.
If you test with 3 different meters the chances of all 3 being U-S are about as high as being hit by lightning in a cellar.

However I've just been given one by my current employer so I'm now looking for the chance to use it. I think I may use my 3 meters to prove the prover just in case it's no good. And then a final poke with an earthed cable.

Woman struck by lightning in Wakefield - Boston News, Massachusettts News, WHDH-TV 7NEWS WHDH.COM