D-5 switchboard (1913 to the 1930s?), F switchboard (1907 to 1911) Up
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The D-5 DC meter was available in a round back-connected switchboard case and available in 2-wire (shown) or 3-wire versions. All of these were used with external shunts. The large hand is the fastest-moving dial and is used where daily readings are taken. As with the service type, this model saw most of its production up to the 1930s but continued to be available on special order into the 1960s.

The Type F switchboard meter was the back-connected version of the Type F AC mercury-motor meter. Like its house-type counterpart, this meter could be used on circuits of all commercial frequencies of its time (25Hz to 133Hz) without requiring different versions for low or high frequencies.

 
D-5 switchboard
Electrical Meterman's Handbook
Type F switchboard
David Turner collection