Types MFS and MFA (1934 to 1954) Previous
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With standardization of meters in 1934, Duncan chose to replace the MD meter with a new meter design. Early MF meters had a large chrome-steel magnet assembly, but this was replaced in 1938 (S/N #2,650,000) with an Alnico magnet assembly which was less suspectible to loss of strength from lightning and power surges. The first MFS and MFA meters had painted register faces but these were replaced in 1936 with aluminum faces which were far less suspectible to fading and peeling from constant exposure to the sun. With S/N 2,600,000, the MFS and MFA meters were redesigned to increase the overload capacity from 300% to 400%. Earlier MFS meters have an insert-type base that allowed Duncan to use the same stator for the MFS and MFA, but this was eventually abandoned. MFA meters made during WWII used a base made of porcelain instead of aluminum. In 1949, the MF-SE was introduced and is the first socket meter to have a capacity of 200 amps.
 
Early Duncan MFA
Don Price collection
Duncan MFS
Photo by David Dahle
Wartime Duncan MFA
Watertown Municipal Utilities collection