[pmmunro]

Dave,

Congratulations on a great "find". It's good to know that such an unusual meter has found its way to someone who appreciates it.

It looks to me like a "customer special" varient on the Model 40 with provision for readily monitoring voltages likely to exceed the standard Model 40 range of 480V. This would suggest a use in connection with three-phase supplies with a nominal voltage of 240/415V or 250/440V (AC). The meter was made in 1947, at a time when mains supplies were not fully standardised so voltage up to 440V would not be unusual.

I would suggest that it was not for well-regulated mains such as we now expect from "the Grid" but even local mains generating and distribution system would not normally be up to 125% of the nominal voltage. Possible applications might have been local generating systems, including ship board, or things like transformer testing or protective relay set-up and testing.

Do you know anything of its provenance? Original owner locations such as Stafford (English Electric/GEC) or Hebburn (Reyrolle) would be good clues to possible applications.

In 1947, much of British industry was still struggling to recover from wartime conditions and I would think this applied to ACWEECO as much as any other. If this speculation is valid, it would not seem likely that there would have been much spare design or manufacturing capacity for "specials" except for large, or potentially large, or influential customers. cf. The "Heavy Duty" for the GWR whic wasn't delivered until they had become BR (Western Region). However, there may have been a Prototype Department which would have been responsible for prearing sample specials. The production methods of the time would have fairly readily accomodated the manufacture of a few sample specials.

It's quite possible that you have a unique meter, the only one of its type ever to be made.

PMM