On Monday, 4 November 2019 15:19:00 UTC, Bob Engelhardt wrote:

I have a Ward-Leonard variac that was originally used, I think, for
theatrical lighting. It is labeled "20A resistive, 14A otherwise". I
suppose "otherwise" means motors, but motors aren't usually run off
variacs. What else could "otherwise" be?

Also, why only 14A?

Fluorescent lighting was also pf not 1. We had a lot of fl lighting on a big variac. It had standard electromagnetic ballasts, and contrary to oft stated opinion it did dim well enough - we knew to not keep it running dimmed, and it blacked out at a low light level, it wasn't perfect but certainly good enough.

Discharge light sources were always pf not 1 in the pre-electronic days, whether fluorescent, carbon arc or mercury vapour. i was never proportional to v with them, and in most cases the ballasts were inductive not resistive. And of course projector carbon arcs ran through mercury rectifiers to give asymmetric electrode heating to minimise the light source size.


NT