Serial number 816925
This Megger Earth Tester was purchased on Ebay recently for £ 5.50 though as is often the case the postage cost was considerably more. The generator was in excellent condition and as can be seen from the pictures was well made and housed in a black Bakelite case and included a leather carrying case with shoulder strap.
Leads are connected to the instrument by depressing the labelled buttons and inserting them into the opening thus exposed. The instrument is designed for 2, 3 or 4 wire resistance measurement. The current leads are to be connected to C1 and C2 and the potential leads to P1 and P2. Provision is rather neatly made via two slide switches to internally connect the potential and current points together when required. The meter has two scales, the inner calibrated from 0 to 20 ohms and the outer from 0 to 500 Ohms, the range being selected by the slide switch adjacent to the meter scales. As a precaution against damage caused by inadvertently connecting the instrument to the live side of the mains rather than the neutral, there is a neon tube to warn the user. In addition readings can only be made when the button on the side is depressed. The neon can be accessed from the base should it require replacement.
View of the generator and other components.
The meter movement is on the left behind the brass plate. The one megohm resistors are in circuit until the push button is depressed to protect the meter. There is a contact which is open when the neon lamp assembly is not in position which acts as a further safety feature. The base of the instrument gives brief instructions for use. I have made a copy of the full instructions here: Earth tester Instruction leaflet Series 4 Megohmmeters are housed almost identical housings but have only two terminals. The 'series 4' range of instruments were introduced [I think] in 1948.
Evershed & Vignoles Ltd of Acton Lane Works, Chiswick. were taken over by AVO Ltd. Avocet House, 92-96 Vauxhall Bridge Road, London, SW1. AVO was a member of the Metal Industries Group of companies. Though known for their Avometer general purpose multimeter, they made a wide range of test gear including valve testers (see elsewhere on my site). The Acton Lane works closed down at about that time - around 1986.
The firm Megger Ltd is now based at: Archcliffe Road, Dover, Kent, CT17 9EN, United Kingdom.