A bit off-topic, but the center-grounded 60/120V configuration had another interesting application in the disco days of the late 1970s. It became a cost-effective solution to 4.8kW of medium-based sign lamps strung up through many feet of wiremold and what seemed to be miles of 14THHN. The idea behind the tapped grounding allowed sets of 16 SCRs on an 8x8 matrix to control three groups of 64 lamps in various patterns, giving control of individual rows and columns of colored lamps. We used a 10kVA, 480-120/240V dry-type transformer, powered from a dedicated 240V circuit, providing 60/120V for the SCR/lamp matrix. This arrangement allowed for switching of both conductors to each lamp, and limited the lampholder voltage to below 150V. [A microprocessor and keypad controlled the SCR-gating patterns.]
It looked great when it was completed, but we didn’t want to think about a sign lamp for a long time. Disco still sucks.
