I-55S and I-55A (1954 to 1988) Previous
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The I-55 superseded the self-contained I-50 meter, increasing the overload capacity from 60A to 100A, partly from using heavier wire on the current coils and introducing better overload compensation (667% instead of 400%). The I-55 also had better voltage compensation that allowed 240V 3-wire meters to be used on 120V 2-wire services without having to calibrate the meter at 120V first. The majority of the I-55 meters were made through the 1960s, but the I-55A and special versions continued to be available for some time after that. I-55S, 2/3 wire version
Photo by David Dahle