Megger BM6 Test Routines? - UK Vintage Radio Repair and Restoration Discussion Forum

OldTechFan96 · 22nd Dec 2019, 2:49 pm

Yesterday I finished restoring a Megger BM6 insulation tester that came with its original leather case and test leads. It was formally owned by the North East Electricity Board, Tynemouth division.

The voltage ranges all measure as they should and resistors can be measured accurately.

What tests can I do with this Megger and how do I do them?

Testing insulation resistance will be the main thing I'd want to do.

Thanks

Red to black · 22nd Dec 2019, 3:20 pm

Have a look on Youtube for electrical testing by Chris kitcher, he has some excellent tutorials.
We normally recommend our apprentices look at his material as part of their learning, he also wrote some definitive books as used for various C&G electrical exams.

It is easier to point you in the direction of these resources than to try and explain things in a rather lengthy post

The Voltimum website: https://www.voltimum.co.uk/ also has some excellent material too, but I think you need to register on that one.

Alistair D · 22nd Dec 2019, 3:35 pm

As a test of accuracy and functionality you could keep a 10Meg 1kV resistor with the meter. Testing this before each use will give assurance the meter is working correctly.

Al

Refugee · 22nd Dec 2019, 5:50 pm

An 11 meg resistor with a volt meter attached is the best thing to use.
It is called a DMM

Alistair D · 22nd Dec 2019, 11:43 pm

Refugee; I presume you mean a DMM with an input resistance of 11Mohms? DMMs come with all sorts of input resistances so you would need to know what the value for the meter you intend to use.

You also need to know how the meter would behave if you accidently stuff 500V into it on it's most sensitive ranges.

By far the most professional, safest and accurate method of checking the calibration is to use a 'standard' resistor as I originally suggested.

Al

Red to black · 23rd Dec 2019, 12:37 am

We have been doing a so called 'soft test' lately @ 250 v, the reason being a lot of LED lighting and USB and surge protected sockets been fitted, yes I know we are supposed to link them out, but practicality kicks in, besides a 250V test is still valid so long as it marked on the test schedule, still the minimum value of 1 Megohm applies.

Refugee · 23rd Dec 2019, 1:13 am

Meters are so cheap these days that you can just measure one with another to check the resistance.
I have several old Meggers and I have never found one to be inaccurate.

Outrun_uk · 23rd Dec 2019, 8:18 am

My day job is repair engineer at a calibration lab. The repair lab is separated from the cal lab which has many thousands of pounds worth of equipment. I have a test box with 1 meg, 5 meg etc etc for a quick check on insulation testers but as mentioned above a DMM is a good test, using my Fluke 73 I would expect pretty near 10Mohm at 500 or 1000v on DC ( voltage should normally be higher, say 520/1050 ish) depending on the UUT. If the UUT passes these basic tests then it is sent for full calibration to the main lab.

HTH,

Kev

OldTechFan96 · 28th Dec 2019, 10:58 pm

Thanks for all the replies so far! Especially when it come to testing the Megger.

By 'test routines' I mean how do I apply the Megger to test aspects of vintage equipment? Transformers IR and resistance to earth is what I had in mind.

TonyDuell · 29th Dec 2019, 3:55 am

In a sense you use it like an ohmmeter, albeit one with a high test voltage.

So for a transformer, connect one lead to the core and the other to the primary winding (either just one lead from that winding or all leads joined together, it shouldn't matter). Turn on the megger or crank the magneto (I am not sure what sort of HV generator your instrument uses) and read the insulation resistance.

For something like a vintage AC radio, one lead to chassis or the earth pin of the mains plug (as appropriate), other lead to live/neutral of the mains plug. Turn the radio mains switch on (you want the transformer connected to the mains cable for obvious reasons) and again activate the HV supply in the Megger.

I am not sure what resistance you consider acceptable. But my experience with old transformers (say) is that they either stand the test voltage with no problems (and have an insulation resistance of 10's of megohms) or break down and test almost as short-circuit (resistance of 10's of k at most!). Sometimes you can even see/hear the sparking where it is breaking down (the blower motors in DEC RK05 disk drives are good for this!)

Refugee · 29th Dec 2019, 11:28 am

The BM6 is a battery type without a magneto.
I have got a scrap one from the same era that was wrecked by leaking batteries.

OldTechFan96 · 29th Dec 2019, 8:57 pm

That's been quite helpful TonyDuell. I have a spare mains transformer and I tested the resistance between the primary and the core and measured 200M ohms. I repeated the test on the HT winding and also measured 200M ohms.

Next, I'll do some L to E or chassis testing.

EDIT: Added some photographs!

There is a few names of former users of this Megger written inside the leather case. My family and I know one of them.

Small world.

22nd Dec 2019, 2:49 pm	#1
OldTechFan96 Octode Join Date: Jul 2017 Location: Newcastle Upon Tyne, Tyne & Wear, UK. Posts: 1,186	Megger BM6 Test Routines? Yesterday I finished restoring a Megger BM6 insulation tester that came with its original leather case and test leads. It was formally owned by the North East Electricity Board, Tynemouth division. The voltage ranges all measure as they should and resistors can be measured accurately. What tests can I do with this Megger and how do I do them? Testing insulation resistance will be the main thing I'd want to do. Thanks

22nd Dec 2019, 3:20 pm	#2
Red to black Nonode Join Date: Mar 2010 Location: Sunderland, Tyne and Wear, UK. Posts: 2,476	Re: Megger BM6 Test Routines? Have a look on Youtube for electrical testing by Chris kitcher, he has some excellent tutorials. We normally recommend our apprentices look at his material as part of their learning, he also wrote some definitive books as used for various C&G electrical exams. It is easier to point you in the direction of these resources than to try and explain things in a rather lengthy post The Voltimum website: https://www.voltimum.co.uk/ also has some excellent material too, but I think you need to register on that one. __________________ I don't suffer from Insanity. I enjoy every minute of it.

22nd Dec 2019, 3:35 pm	#3
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Megger BM6 Test Routines? As a test of accuracy and functionality you could keep a 10Meg 1kV resistor with the meter. Testing this before each use will give assurance the meter is working correctly. Al __________________ I won't tell you how I discovered that.

22nd Dec 2019, 5:50 pm	#4
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Megger BM6 Test Routines? An 11 meg resistor with a volt meter attached is the best thing to use. It is called a DMM

22nd Dec 2019, 11:43 pm	#5
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Megger BM6 Test Routines? Refugee; I presume you mean a DMM with an input resistance of 11Mohms? DMMs come with all sorts of input resistances so you would need to know what the value for the meter you intend to use. You also need to know how the meter would behave if you accidently stuff 500V into it on it's most sensitive ranges. By far the most professional, safest and accurate method of checking the calibration is to use a 'standard' resistor as I originally suggested. Al __________________ I won't tell you how I discovered that.

23rd Dec 2019, 12:37 am	#6
Red to black Nonode Join Date: Mar 2010 Location: Sunderland, Tyne and Wear, UK. Posts: 2,476	Re: Megger BM6 Test Routines? We have been doing a so called 'soft test' lately @ 250 v, the reason being a lot of LED lighting and USB and surge protected sockets been fitted, yes I know we are supposed to link them out, but practicality kicks in, besides a 250V test is still valid so long as it marked on the test schedule, still the minimum value of 1 Megohm applies. __________________ I don't suffer from Insanity. I enjoy every minute of it.

23rd Dec 2019, 1:13 am	#7
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Megger BM6 Test Routines? Meters are so cheap these days that you can just measure one with another to check the resistance. I have several old Meggers and I have never found one to be inaccurate.

23rd Dec 2019, 8:18 am	#8
Outrun_uk Heptode Join Date: Aug 2009 Location: Liverpool, Merseyside, UK. Posts: 705	Re: Megger BM6 Test Routines? My day job is repair engineer at a calibration lab. The repair lab is separated from the cal lab which has many thousands of pounds worth of equipment. I have a test box with 1 meg, 5 meg etc etc for a quick check on insulation testers but as mentioned above a DMM is a good test, using my Fluke 73 I would expect pretty near 10Mohm at 500 or 1000v on DC ( voltage should normally be higher, say 520/1050 ish) depending on the UUT. If the UUT passes these basic tests then it is sent for full calibration to the main lab. HTH, Kev

28th Dec 2019, 10:58 pm	#9
OldTechFan96 Octode Join Date: Jul 2017 Location: Newcastle Upon Tyne, Tyne & Wear, UK. Posts: 1,186	Re: Megger BM6 Test Routines? Thanks for all the replies so far! Especially when it come to testing the Megger. By 'test routines' I mean how do I apply the Megger to test aspects of vintage equipment? Transformers IR and resistance to earth is what I had in mind.

29th Dec 2019, 3:55 am	#10
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,215	Re: Megger BM6 Test Routines? In a sense you use it like an ohmmeter, albeit one with a high test voltage. So for a transformer, connect one lead to the core and the other to the primary winding (either just one lead from that winding or all leads joined together, it shouldn't matter). Turn on the megger or crank the magneto (I am not sure what sort of HV generator your instrument uses) and read the insulation resistance. For something like a vintage AC radio, one lead to chassis or the earth pin of the mains plug (as appropriate), other lead to live/neutral of the mains plug. Turn the radio mains switch on (you want the transformer connected to the mains cable for obvious reasons) and again activate the HV supply in the Megger. I am not sure what resistance you consider acceptable. But my experience with old transformers (say) is that they either stand the test voltage with no problems (and have an insulation resistance of 10's of megohms) or break down and test almost as short-circuit (resistance of 10's of k at most!). Sometimes you can even see/hear the sparking where it is breaking down (the blower motors in DEC RK05 disk drives are good for this!)

29th Dec 2019, 11:28 am	#11
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Megger BM6 Test Routines? The BM6 is a battery type without a magneto. I have got a scrap one from the same era that was wrecked by leaking batteries.

29th Dec 2019, 8:57 pm	#12
OldTechFan96 Octode Join Date: Jul 2017 Location: Newcastle Upon Tyne, Tyne & Wear, UK. Posts: 1,186	Re: Megger BM6 Test Routines? That's been quite helpful TonyDuell. I have a spare mains transformer and I tested the resistance between the primary and the core and measured 200M ohms. I repeated the test on the HT winding and also measured 200M ohms. Next, I'll do some L to E or chassis testing. EDIT: Added some photographs! There is a few names of former users of this Megger written inside the leather case. My family and I know one of them. Small world. Attached Thumbnails Last edited by OldTechFan96; 29th Dec 2019 at 9:09 pm.