Proving unit

[oneofthedamned]

I have just purchased a proving unit made by black star but when I stick my volt tester (fluke 120 with digital display) in it only lights up 2 neons and reads 31v.

If I stick in my multimeter it reads 241, if I stick my clamp meter leads in I get 243 and my Megger reads 244.

When I test a mains supply it reads over 230v every time, is somthing broken? or could it be somthing to do with the last line of the overview which I have only just noticed while setting up the web page link?

" This product will only work with test voltage indicators that have an input impedance of greater than 120kΩ"

 

[Mr Sworld]

It would seem that the impedance of the T120 is the problem. Flukes technical manual for the tester doesn't mention what the input impedance is however.

Could be worth a phone call to Fluke Technical helpline to ask them though.

 

[Apache]

could your volt tester be duff?

 

[SPECIAL LOCATION]

Doesn't the write up say...

A handheld, battery powered proving unit able to provide a nominal 240Vdc, 2mA source to prove the integrity of neon type test voltage indicators

Neon type testers?? ?:|

 

[oneofthedamned]

Doesn't the write up say...Neon type testers?? ?:|

So is there a difference in how led's ond neons indicate voltage?

I am new to all this and although I have answered a few multiple choice questions I have not yet fully grasped all this impedance, resistance and reactance science stuff yet.

As I said in my first post it reads fine on the mains voltage.

Is this some sort of AC/DC thing or is as Apache suggests my tester is duff?

 

[steptoe]

Doesn't the write up say...Neon type testers?? ?:|

will this work with my screwdriver then??? :^O :^O:^O

 

[KR Sol]

I have the same problem with my Fluke T140. I think Mr Sword is correct the meter is putting a load (impedance) onto the circuit which is pulling the voltage down, very useful for fault finding but not on a proving unit. I have another meter I use, if there is not a Known supply I can test my T140 on before starting a job. But my first choice is still my T140 nice bit of kit (in my opinion anyway)

 

[oneofthedamned]

" This product will only work with test voltage indicators that have an input impedance of greater than 120kΩ"

This would indicate then that that higher the impedance the better. But surely the higher the impedance the lower the voltage reading? ?:|

I should have paid more attention in physics.

 

[septiclecky]

Had a quick look on the web regarding the 120 and 140, sorry to say that they do not conform to HSE guidance note GS38 which states that the maximum probe tip should be 4mm.

 

[Apache]

Just a suggestion from a non-spark, but if you want to verify your device is working correctly then why not test it on the circuit before you isolate it?

Or if in doubt after isolation go to the meter and test it before isolation!

Could I have saved you

 

[KR Sol]

Had a quick look on the web regarding the 120 and 140, sorry to say that they do not conform to HSE guidance note GS38 which states that the maximum probe tip should be 4mm.

Some of the data sheets are not clear about the probe tips of the T120/140 and the pictures are showing long probe tips but mine have only got 2mm tips and if you have a look at http://www.sjelectronics.co.uk/acatalog/T100.pdf it states 'Compliant with GS 38' but I can see why there is confusion as the ad's and write ups are not clear.

 

[septiclecky]

Just a suggestion from a non-spark, but if you want to verify your device is working correctly then why not test it on the circuit before you isolate it? Or if in doubt after isolation go to the meter and test it before isolation!

Could I have saved you

 

[oneofthedamned]

Like KR sol's tester mine has only 2mm of tip showing so I am sure its ok under GS38. But will it satisfy all the health and safety bureaucracy that my known source is only 30v?, at least its known.

 

[Mr Sworld]

An ideal voltmeter has infinite input impedance, meaning that it draws zero current from the circuit under test. This way, there will be no 'impact' on the circuit as the voltage is being measured. The more current a voltmeter draws from the circuit under test, the more the measured voltage will "sag" under the loading effect of the meter, like a tire-pressure gauge releasing air out of the tire being measured: the more air released from the tire, the more the tire's pressure will be impacted in the act of measurement.

 

[oneofthedamned]

What a fantastic analogy Mr S. This electrickery thing would be a whole lot easier with a few lecturers in colleges who could explain things as simply as that.Applaud Smiley

"One good analogy is worth three hours discussion."

 

[Apache]

Would not comply with most safe isolation procedures as you have to test your test lamp on a known source (proving unit) then check circuit is dead with test lamp after isolation has been carried out, you then have to test your test lamp on the same known source (proving unit) again to prove test lamp is working ok.It may seem long winded but that is the normal practice in most factories now, better to be safe than sorry.

If you are at the point of isolation there's bound to be something live going to the means of isolation! In a domestic setting, as I suggested above, turn off main switch on CU the incoming tails are live.

If in a factory it's a single isolator for a motor there will be a live going in and a dead cable coming out. Other than in the even of total power loss would this not be the case, and then care must be used as installation could become live whilst you work on it!

 

[oneofthedamned]

If in a factory it's a single isolator for a motor there will be a live going in and a dead cable coming out.

The isolator for the motor of which you speak is usually a red circular switch which has a couple of holes that allign in the off position so you can padlock it. You then remove the cover of the motor, poke it with your voltage tester and the then prove that your voltage tester works, no live wires anywhere do you

(a) dismantle the isolator switch to gain access to some live wires

(b ) roam around the factory looking for another known live source

© reach into your tool box prove with proving unit

 

[steptoe]

TBH guys, I tend to use Apaches method, put my meter on a known live source before and after.

how do you know your proving unit hasnt went belly up between the first and second proving?

personally I think they are a waste of time and money, if your that concerned just use 2 (or more) voltage meters at the point of isolation/work, more reliable methinks than simply relying on ONE proving unit(putting out a punitive voltage/current that is derterminate of the impedance of your voltage meter to work at all!) for all your test meters.

you could always use the tried and tested finger flick method, very reliable and I do it EVERY time, after metering of course, just to be certain.

 

[nsparks]

these seem to do the job gloves, especially when working on live tails.

 

[oneofthedamned]

you could always use the tried and tested finger flick method, very reliable and I do it EVERY time, after metering of course, just to be certain.

Hey Mr Steptoe thought you might like a new hat.