I picked up some '70s era GE NEMA 1 magnetic contactors, NOS, military spares. They have overload relays that accept heater inserts and are adjustable within ±15% of nominal via a thumbwheel. Clearly the heater inserts are literally just that - they heat the inside of the overload relay. Beyond that, though, I'm stumped. I'm trying to figure out how these overload relays work. Anyone know? The overload relay number is CR124 if that helps.
Grant
A contactor and an overload relay together are called a starter.
The heaters in the overload relay are interchangeable (to match the current requirements of the circuit), and are intended to heat either a bi-metalic element or a meltable metalic compound (later models may be fully electronic) which allows an internal switch (normally used to carry current through the contactor coil) to open which breaks the holding curcuit and allows the contactor points to seperate.
dennis in nca
Ah. Bimetallic strip. Makes sense. Doesn't explain how the thumbwheel works, but gives me a general idea.
Grant
Ignoramus17333 wrote:
probably adjusts tension on the strip
i
A little latching bar sits on the thumb wheel to hole the points closed... When the strip heats up from to much current it releases the thumb wheel letting it spin letting the latch fall off the wheel letting the points come open...
Correct. More tension, faster trip.
Gunner
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