Megger Major Questions - UK Vintage Radio Repair and Restoration Discussion Forum

Sam · 20th Mar 2005, 11:59 pm

I was given a hand-cranked Megger Major today in its leather case, with its test leads. It is in a metal silver-painted wrinkle-finish case, with a pale-blue bottom half. I guess it is from about 1972, as a price given on the operating card is "10p (2s)".

What EXACTLY are they useful for - I guess checking how dodgy an old mains cable is! I know you can (somehow) check if a transformer is breaking-down. Is this primary to secondary though? I want to use this thing, especially as I was given it!
My question is, where should the needle sit on the meter?

It usually seems to hover about 1/3 to 2/3 of teh way accross the scale. Is this OK? I have played with it a bit, and it seems to give believeable results - 100Mohm resistance for a brand-new bit of mains fles (on the 500v Mohm x 1 range).

Sam

joe · 21st Mar 2005, 12:41 am

Hi Sam

"Meggers" (Trade Mark) are insulation testers. They measure resistance, but with a high voltage applied to the item under test. Full scale deflection is zero ohms, the other end of the scale will show 100 to 200 megohms. The big difference between these and an ordinary meter is that a good wind of the handle can produce 500v! The Megger Major may even be higher. Take care, they really can make you jump.

As for the meter movement it is some arrangement of two coils at right angles and there is no hair spring so the needle will come to rest rather randomly when its not in use.

Joe

jim_beacon · 21st Mar 2005, 12:43 am

Sam,

I have a document at:

www.g1jbg.co.uk/service.htm

which gives the theory and some of the uses of a Megger.

Jim.

Ed_Dinning · 21st Mar 2005, 1:38 pm

Hi Sam, In my day they were used to test unwary apprentices at Reyrolle, so note the eatlier warning. Ithing the Major Megger was good for 1000volts. It should be marked on the case somewhere.

Ed

Sam · 21st Mar 2005, 3:30 pm

Quote:

Originally Posted by Ed_Dinning

Hi Sam, In my day they were used to test unwary apprentices at Reyrolle, so note the eatlier warning. Ithing the Major Megger was good for 1000volts. It should be marked on the case somewhere.

Ed

Yup, 100, 250, 500, and 1000V 'ranges'. Wonder if I can draw much of a spark between the terminals!

Probably best not to try.

Thanks for the reassurance about the needle Joe. I just wanted to make sure the movement was OK. A clean up of the Megger and leather case, and it should look quite neat! I downloaded that information from Jim Beacon's site, and will read it later.

Sam

Ed_Dinning · 21st Mar 2005, 6:46 pm

Hi Sam, not much of a spark I'm afraid. If as an aprentice you were subject to the insulation resistance test the trick was to hold the terminals very tightly, your very low resistance than reduced the voltage and nothing was felt. A weak grip would have you jumping!

Ed

20th Mar 2005, 11:59 pm	#1
Sam Hexode Join Date: Apr 2003 Location: Higham-on-the-Hill, Leicestershire, UK. Posts: 338	Megger Major Questions I was given a hand-cranked Megger Major today in its leather case, with its test leads. It is in a metal silver-painted wrinkle-finish case, with a pale-blue bottom half. I guess it is from about 1972, as a price given on the operating card is "10p (2s)". What EXACTLY are they useful for - I guess checking how dodgy an old mains cable is! I know you can (somehow) check if a transformer is breaking-down. Is this primary to secondary though? I want to use this thing, especially as I was given it! My question is, where should the needle sit on the meter? It usually seems to hover about 1/3 to 2/3 of teh way accross the scale. Is this OK? I have played with it a bit, and it seems to give believeable results - 100Mohm resistance for a brand-new bit of mains fles (on the 500v Mohm x 1 range). Sam __________________ Can he lead a Normal life, Doctor? No, he will be ... an Engineer.

21st Mar 2005, 12:41 am	#2
joe Rest in Peace Join Date: Apr 2003 Location: Edgware, North London. Posts: 307	Re: Megger Major Questions Hi Sam "Meggers" (Trade Mark) are insulation testers. They measure resistance, but with a high voltage applied to the item under test. Full scale deflection is zero ohms, the other end of the scale will show 100 to 200 megohms. The big difference between these and an ordinary meter is that a good wind of the handle can produce 500v! The Megger Major may even be higher. Take care, they really can make you jump. As for the meter movement it is some arrangement of two coils at right angles and there is no hair spring so the needle will come to rest rather randomly when its not in use. Joe

21st Mar 2005, 12:43 am	#3
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: Megger Major Questions Sam, I have a document at: www.g1jbg.co.uk/service.htm which gives the theory and some of the uses of a Megger. Jim.

21st Mar 2005, 1:38 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: Megger Major Questions Hi Sam, In my day they were used to test unwary apprentices at Reyrolle, so note the eatlier warning. Ithing the Major Megger was good for 1000volts. It should be marked on the case somewhere. Ed

21st Mar 2005, 6:46 pm	#6
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: Megger Major Questions Hi Sam, not much of a spark I'm afraid. If as an aprentice you were subject to the insulation resistance test the trick was to hold the terminals very tightly, your very low resistance than reduced the voltage and nothing was felt. A weak grip would have you jumping! Ed