AVI (Approved Voltage Indicator) - Common Misconceptions

[I2C]

Hi Guys!

I've worked with a few qualified-electricians recently and I'm shocked with the large-scale misconceptions regarding the proper safe-isolation procedure, particularly concerning the function of an AVI (Approved Voltage Indicator).

During the last few weeks I've met several domestic qualified-electricians who have told me not to test between line-earth & neutral-earth because this will trip the RCD/RCBO; they have all advised me to only test between line-neutral. When I confronted them with actual facts and figures, they all refused to acknowledge my comments, arguing otherwise without any form of proof, which I found bizarre?

I'd like to confirm that their advice is incorrect, and I can prove it factually. I use a Kewtech KT1790 Approved Voltage Indicator which seems fairly common amongst electricians, and I'll base my comments on this:

• The Kewtech KT1790 data-sheet states "This instrument can make measurements between L-PE without tripping RCDs".
• The Kewtech KT1790 data-sheet states that the devices internal-resistance is 200,000 Ohms. Based on this value, we can calculate the current-flow using basic Ohm's Law:
  - 230V - 1.15 mA (Standard RMS voltage used for design calculation)
  - 245V - 1.22 mA (Highest likely RMS voltage measured)
  - 500V - 2.50 mA (Exceeding AC Peak Voltage)
  
• A common RCD used in domestic properties for additional-protection has an operating-current of 30mA (much greater than the current produced while testing).
• Rarely in specialised circumstances a 10mA RCD is used for certain applications (much greater than the current produced while testing).

To conclude, the AVI (Approved Voltage Indicator) is perfectly suitable and safe for use when performing the proper safe-isolation procedure (including testing between line-earth and neutral-earth) as explicitly explained within the products data-sheet, and also proven through simple calculation of it's specifications.

I'm interested to find out if anyone else has encountered this problem? If so, to share this information.

 

[Wilko]

Shocking ! (sorry )
I can't speak for those you've mentioned, but for my part it's always test all to all .

 

[Loki]

See page 18 of pdf

Niceic pocket guide 5

It clearly says to test between:

Earth and Line
Neautral and Line
Earth and Neautral

 

[snowhead]

They've had experience of older basic testers (pre LED) which did trip RCD / RCBO and not bothered to try with the newer non trip ones.

 

[The Ghost]

I've worked with a few qualified-electricians recently and I'm shocked

You say you are shocked, so much for safe isolation. If someone you work with wishes to chance getting an electric shock just make sure you know appropriate resuscitation techniques. Apart from warning someone what can you do. As for Popular Misconceptions, it certainly has not been my experience that this is endemic in the trade most people I have met take all due precautions. I also add to persons who sometimes work/train with me that they should test between local metal work and earth to ensure there are no stray voltages such as suspended ceilings when working on klik fittings above. I have found 120v on suspended ceilings before. So think about that as well.

 

[SparkyChick]

The Fluke T-150 has an RCD trip function built in, so you can test at a circuit and trip the RCD by pressing two buttons (one on the dumb probe and one on the main unit).

But regardless, they are wrong. Safe isolation requires a full test of L-N, L-E and N-E.

 

[telectrix]

shoot them down with this then.

example is a lost N, so test L-N, no reading. then get a belt off the L. maybe their thinking is because L-E and N-E tests are covered in week 6 of their 5 week course.

 

[telectrix]

shoot them down with this then.

example is a lost N, so test L-N, no reading. then get a belt off the L. maybe their thinking is because L-E and N-E tests are covered in week 6 of their 5 week course.

 

[SparkyChick]

I like double posts as I can rate it twice... I agree and it's funny

 

[Jay Sparks]

I like double posts as I can rate it twice... I agree and it's funny

That's how he gets his post count so high.lol

Jay

 

[Simonslimline]

How did these so called "sparks" pass the AM2 carrying out "safe isolation" incorrectly?

 

[ruston]

@12c . Get a good look at their faces and if you are on a job with them take extra care.

 

[Pete999]

How did these so called "sparks" pass the AM2 carrying out "safe isolation" incorrectly?

 

[Des 56]

First they are very very wrong
Second,my advice for anyone interested, learning or even qualified in electrics, it is to never under any circumstances accept assurance off anybody but yourself that something is safe or even advice on how to make something safe

Its your health and well being at stake and its too important to trust to anybody irrelevant of whether they appear to know what they are doing

 

[ruston]

And even when you know it is off , work as if it isn't.

 

[telectrix]

fish was off, but they ate it.

 

[Deleted member 26818]

I take it that this is only a problem when one RCD covers multiple circuits?

 

[marconi]

And even when you know it is off , work as if it isn't.

Sir, I think this would be worth elaborating for EF readers giving examples of what you do. The electricians doing our current extension wore dextrous rubber gloves for example - the plumbers wore similar gloves more I think for the grip and prevention of cuts.

It might be these:

Ansell ActivArmr ActivArmr Electricians Gloves Grey Large - https://www.screwfix.com/p/ansell-activarmr-activarmr-electricians-gloves-grey-large/99723

The organisation I worked for taught the 'one hand rule' for example to avoid across the chest/heart shock currents.

 

[HandySparks]

And even when you know it is off , work as if it isn't.

The obvious one is to always use insulated snips for cutting cable, even if you know it's dead. One day it won't be.

Same for insulated screwdrivers. If you get into the habit, then it won't go so badly for you when, eventually, you tighten a terminal that should be dead, but isn't.

 

[telectrix]

i always check tightness of terminations when live. if it sparks, it's not right. therefore the vde drivers are a must, otherwise i might get a tingle that wakes me up.

 

[1Justin]

For I2C : My Dilog AVI has an 18K input impedance. High enough normally of course (if no other leakages), but too low for it to be driven anywhere close to 230V by a Martindale proving unit (which can only drive about 3mA, - hence about 60V on testing the AVI).

 

[telectrix]

i reallyneed to check the input impudence of my AVO 8.i forgot what it was back in 1982.

 

[PEG]

I find it hard to believe,that several electricians suggest the test described,by the OP...one numb one...but plural?

The fundamental requirements,are to both understand how the test equipment functions,and how to use it,to discover whether safe or not.

Experience of the various scenarios,where line voltage can occur,would make ALL the necessary combinations of testing,second nature.

Line/neutral reversed,a live neutral,live earth,or all live...are all possible or probable occurrences,and all testing should indicate such.

The gentlemen advising otherwise,have possibly never inspected a connected burger bar,by first putting one probe on the yard surface,and the other on it's brightwork

 

[ipf]

If you're testing for isolation it should be isolated. If so, why worry about an rcd tripping.
It should all be dead, so test it all.
Fault finding may be different.....but it should have tripped, anyway.

 

[dmxtothemax]

my papa used to say - Never try to argue with a fool, they will only force you down to there level, then beat you with experience !
Some people just don't want to listen for what ever reason, you just learn not to even try with those sort of people !

 

[PEG]

Just an appendage,to my previous post,which mentioned correct understanding of a test instrument,would be to remember that an AVI is not only used to check for safe isolation.

It is as handy,though not it's primary use regarding this conversation,for proving a voltage present.

A quality AVI,with maybe resistance and DC capability,can be a fine,compact troubleshooting device.

I have an old TPT220,which stays in the glove box,or hand luggage...and it's paid for itself a hundred times over

 

[static zap]

Some people just don't want to listen for what ever reason, you just learn not to even try with those sort of people!

I still feel the urge to get them to notice -some effort was used...and wonder why ! (or/Not)
Safe .. negligible volts anywhere !