Insulation tester – some guidance please

[Ian HewsonParticipant @ianhewson99641]

In the late 50s as an apprentice in the YEB meter test room it was a joke to get the lad to hold the wires of the 1000volt megger, but they could not understand why I could hold on as they wound.

So long as I held tightly I only got a tickle, laugh on them.

It was a different story with the later electronic version though, I could not hold that.

[Harry WilkesParticipant @harrywilkes58467]

Posted by Nick Clarke 3 on 20/12/2018 14:35:53:

Posted by Harry Wilkes on 19/12/2018 22:18:44:

Ah a megger 500v or a 1000v would break the will of any apprentice

H

A long time ago I used to drive for a firm that repaired fridges. One of the engineers used to get a kick out of asking an apprentice to hold a wire from a 'windy' megger which he then wound up and shocked the guy.

The apprentices learnt to keep away from him when he was in a 'joking' mood and recognised the megger as the source of his fun.

So what happens next – engineer buys a push button megger that they don't recognise and the cycle starts over!

[Harry WilkesParticipant @harrywilkes58467]

Posted by Ian Hewson on 20/12/2018 15:16:48:

In the late 50s as an apprentice in the YEB meter test room it was a joke to get the lad to hold the wires of the 1000volt megger, but they could not understand why I could hold on as they wound.

So long as I held tightly I only got a tickle, laugh on them.

It was a different story with the later electronic version though, I could not hold that.

The Forman at the very first place I worked could also hold the ends of the megger leads and his party trick to show us apprentices why he was the Forman was told hold one of the HT plug lead on a car in one hand and touch the end of the spark plug with the other hand whilst the engine was running

H

[Mike PooleParticipant @mikepoole82104]

Posted by Phil Whitley on 19/12/2018 21:16:29:

Mike Poole, an insulation tester is an essential tool when working on electric motors and electric heaters, which almost always fail "down to earth" They are used for final insulation tests on domestic installations, but that is about all. Absolutely essential tool for fault finding, but NOT on electronics!

Hi Phil, after over 40 years of electrical and electronic fault finding I stand by my comment on the need for an insulation tester, it spent most of its life in the equipment cupboard whereas my fluke multimeter spent most of its life in my pocket. As an apprentice motor failures were much more common but as with most things they have become much more reliable so that failure is now very rare, the last facilty I worked on probably has 10,000 motors installed and motor failure is very rare and determining failure rarely required an insulation tester or a bridge megger. As small motors are not economical to repair the precise nature of failure is not worth the time and effort to diagnose. I am not proposing that a multimeter does what an insulation tester is for, just that it is a more useful tool most of the time. My immersion heater didn’t need anything more than a multimeter to inform me the element was down to earth and open circuit but that was a particularly catastrophic mode of failure. Tracing the condensation in a socket box that was tripping the RCD very definitely did need an insulation tester, it’s always useful to have the right tool for the job but in my experience an insulation tester is rarely required but when it is it nothing else will do.

Mike

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Stuart Bridger on 20/12/2018 13:13:11:

Good Information here **LINK**

.

Thanks for that, Stuart

MichaelG.

[Phil WhitleyParticipant @philwhitley94135]

Yes Michael Giligan, good info, my wooden case model is the safety bridge megger, the second of the three pics. Mike Poole, not disagreeing with you, all you really need to tell a motor is gone is your nose! It may be that more modern installations than the ones I worked on in the sixties and seventies have better insulation, and fault to earth less, but a lot of what I did was in factories where the common denominator was wet! turkey and other food processing, and gravel pits, to mention a couple. earth leakages were very common. Today I have thank goodness retired from all that, and spend my time building, repairing and playing with machines and machine tools, much more rewarding, and a damn sight warmer and drier.

Edited By Phil Whitley on 20/12/2018 20:20:12

[Simon Williams 3Participant @simonwilliams3]

If I remember it right, the IEE Wiring reg's say the test source for testing insulation of low voltage equipment energised at 230 V AC must provide not less than 500 volts DC into a load of 1 megohm, other loads pro rata. Sorry gents but I don't think your windey Meggers do this.

I take Phil's point about liking analogue meters – I happen to prefer my digital, but it's horses for courses. However I can't let the assertion that a simple multimeter is sufficient to prove the equipment is safe to energise go unchallenged, the Regs say otherwise. By all means go looking for a fault with a DVM, but the testing to prove that it's safe to plug it in to the mains has to be done at an elevated voltage. Phil's right, all you often need to find there is a fault is a sense of smell!

The use of 5KV (flash testing) would only be warranted if the equipment was being re-designed or modified, or there was some reason to believe that a simple insulation test was insufficient. Or you've got a particularly difficult customer!

Mince Pies out for Santa + 4 days!

[Phil WhitleyParticipant @philwhitley94135]

That is what my windey megger produces Simon!

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Emgee on 20/12/2018 10:31:12:

I believe the Megger linked to by Michael is not working correctly, the meter is indicating a reading when not being cranked, without operating the handle the needle will be at 1 end of the scale, don't remember which end but I used that type of instrument for a few years before digital meters were available.

Emgee

This is not a fault. The meter movements in Meggers do not have a return spring and the pointer "floats" when the handle is not turned. The movment has two coils, a voltage coil that drives the pointer towards infinity and a current coil that drives it towards zero. It's a ratiometric instrument so the voltage does not have to be spot-on or zeroed like you do on an AVO.

Robert G8RPI.

[not done it yetParticipant @notdoneityet]

Posted by Harry Wilkes on 20/12/2018 15:48:21:

Posted by Ian Hewson on 20/12/2018 15:16:48:

In the late 50s as an apprentice in the YEB meter test room it was a joke to get the lad to hold the wires of the 1000volt megger, but they could not understand why I could hold on as they wound.

So long as I held tightly I only got a tickle, laugh on them.

It was a different story with the later electronic version though, I could not hold that.

The Forman at the very first place I worked could also hold the ends of the megger leads and his party trick to show us apprentices why he was the Forman was told hold one of the HT plug lead on a car in one hand and touch the end of the spark plug with the other hand whilst the engine was running

H

1000 volts is chicken feed! We were often shocked by 6kV pulses. Now, the Van der Graff generator could easily make your hair stand on end.

We once had car seat covers that would cause a flash to earth across one’s shoe soles, after extracting oneself from the car, especially if one was wearing a synthetic shirt. Had to hold the car door, while getting out, to dissipate the static. They did not last long.

They don’t recommend playing with high voltages, these days, as it can reduce one’s favourable response in the case of ever needing to be defibrillated.

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