Why are proving units so expensive?

[brian.l.child]

Good afternoon all, my query is about proving units. Several firms make them but they all seem quite expensive is it because not many are sold as an Electronics engineer I can't see the components costing a lot or is there some other reason. As I am starting up again a proving unit is a long way down the list surely combination sales would be a better bet where you buy the Voltage tester and the proving unit is part of the kit. Brian

 

[telectrix]

i always use the incoming side of the main switch as a proving unit. why buy when there's a free one there already?

 

[brian.l.child]

Well I never thouight of that one, Thank you.

- - - Updated - - -

Sorry about the extra I. Its always about me. Brian

 

[Guest111]

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!

 

[Steve_P]

I have one, , got it as a freebie a couple of years ago, grabbed it on my last assessment and my assessor asked why I wasn't using the incomming supply. Said that I thought that's what they expected as I would usually use the supply. Got a sort of knowing look so I put the unit back in the bag and there it stays.

 

[cogsey133]

I got one as a freebie too and i have so never used it ever....lol. Incoming side it is for me too

 

[DurhamSparky]

only proving unit i use is for checking that our HV equiptment is dead...!!

LV units are expensive and as already said... check against the incoming supply!

 

[Top Cat]

And if you don't get a light from incoming side you can always wet your finger and prod, you will soon know if it's live! Lol

 

[nickblake]

problem is you need a proving unit for your proving unit to prove that the first one is working question is the battery in the proving unit flat or are the prods faulty , i got one ,found the prods would fit through the holes great eh

 

[snowhead]

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.

 

[SJD]

Apart from the cost, some proving units are not well designed. I've got a Kewtech one, and my AVI probe tips won't fit into the proving unit holes, if I keep the guards on the AVI and just have 2mm tips exposed. So I end up using the AVI with much larger exposed tips (10 to 15mm), well beyond what GS38 would have us use. I think it should be possible to design a much better proving unit at a much cheaper price.

 

[DurhamSparky]

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

then normally i would be happy to work unaided if there was no supply!

 

[brman]

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!

 

[Adam W]

then normally i would be happy to work unaided if there was no supply!

Yes but how do you know if there's no supply?

 

[Phil]

they should at least be 20% cheaper imo. they should be vat exempt

 

[Geordie Spark]

they should at least be 20% cheaper imo. they should be vat exempt

I remember when VAT was first introduced & my old gaffer was having a rant about it: "Value added tax?? .... it adds nothing to the value of anything, it only adds tot he price .... it should be called Price Added Tax !!!"

And there was two different rates wasn't there? One was 8% I think, but not sure what the other rate was, but it was higher. I seem to remember the lower rate being applied to the toys that you put in budgies cages if it didn't have a mirror, but the higher rate applied if it did. (something like that anyway)

 

[MarkieSparkie]

The history of UK VAT here:
Value Added Tax (United Kingdom) - Wikipedia, the free encyclopedia
[url]http://www.ifs.org.uk/fiscalFacts/taxTables
[/URL]

 

[Mark_Burgess]

Yes but how do you know if there's no supply?

A lack of Service head, Meter, Tails, fuse.

 

[Adam W]

A lack of Service head, Meter, Tails, fuse.

Yes, that would be a good indication.

 

[Air Conditioner]

A lack of Service head, Meter, Tails, fuse.

What are they?..........................Only joking!!:smiley2:

 

[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

 

[the pict]

£50 plus vat is the cheapest I'V seen I need to get one for my 1st assesment soon so when the guys gone it'll be out with battery back in its box till next year I mean who the hell is going to test the tester, go up a ladder test the incoming tails, turn it of test the tails test the out side of the iso go down the ladders test the tester go back up the ladders and test the dead side again I mean whats the punter going to think, jeez I mean if the little lights go out it dead ffs
Pict

 

[Remooc]

£50 plus vat is the cheapest I'V seen I need to get one for my 1st assesment soon so when the guys gone it'll be out with battery back in its box till next year I mean who the hell is going to test the tester, go up a ladder test the incoming tails, turn it of test the tails test the out side of the iso go down the ladders test the tester go back up the ladders and test the dead side again I mean whats the punter going to think, jeez I mean if the little lights go out it dead ffs
Pict

Hello first post on the forum,
I have just had my yearly inspection with the nic and was asked to do safe isolation and at the end I told the inspector that I was checking the incoming side to make sure the voltage indicator was still working and his reply was "very good making sure that the unit is still working so you know that you are now safe to work" looks like proving units can stay on the shelves.

 

[Rob Smith 643]

I got one 'free' when I bought a Martindale VT a little while ago, foolishly believing it would be a Martindale brand proving unit. Wrong! Piece of cack arrived instead. But it works and was free, though a little awkward to use - so I generally don't. :lipsrsealed2:

 

[the pict]

one went for 26quid on ebay, I got a martindale 690 for £40ish there
Pict