Evershed & Vignoles Series 2 Bridge Megger

Ser no. 1027220


             bridge megger

Megger/Varley/ Bridge switch on left and ratio switch on right

bridge megger

meter dated October 1955

bridge megger

Evershed & Vignoles Megger series 2. This is a very common and robust instrument housed in a cast metal housing unlike the earlier series 1 range of instruments.  It can be used as a conventional insulaton tester, a conventional resistance bridge and for the "Varley" method of line test. This simplified diagram shows how this is accomplished. In common with other Megger models an RC snubber is connected across the generator terminals. In this model, and I suspect others, this comprises a 4700 ohm resistor in series with a 0.1mFD capacitor.


bridge megger

This instrument is one of a number given to me by Martin Harrison which belonged to his father who was a a Chartered Electrical Engineer. He collected both old electrical test equipment and due to his name (John Harrison) old clocks. Martin thought his father would have been pleased with his items been given a new home and owner.

I found the instrument to be in working order and accurate when tested against a range of standard resistors on both the Bridge and Megger modes of operation. The open circuit output on the Megger switch position was 488 volts and on the Bridge position in the region of 20 to 30 Volts.

A lighter, more modern version (not in my collection) dating from the 1970s is shown below:

bridgemeggerbridgemegger

The "Megger" instrument for measuring the insulation resistance of electrical devices was introduced by the British firm of Evershed and Vignoles in 1903. The name comes from the fact that the insulating resistance of a properly-designed appliance is in the range of tens and hundreds of meghoms. The crank on the end powers a generator connected to a specially-designed meter. GB patent number 400728 was granted in 1933.