Today, I replaced an old, single pole electrical switch with a new one. The old one worked just fine. It was originally installedl when the building was built in 1957. I replaced it with a pilot lighted switch so it would be easier to locate in the dark. ( this is in the basement of a commercial building). The switch never made any “clicking” sound when flipped on or off. The terminals were located on the front of the switch, rather than on the side.
Sooo, when I returned home, I took it apart to see how it functioned. This is what I found:
The switch is a GE ( General Electric). It has a plastic housing on the back. The front mounting strap was not pop riveted on, but rather held in place by 2 small screws. I removed the mounting strap and the plastic toggle(on-off button) fell out . Inside was a metal disc, approx 1/2 inch thick and having a diameter of approx 5/8. This metal disc looked as though it was 2 halves joined together, and in the middle of these 2 halves, a band of glass ( or plastic?) was glued in between.
This disc was wedged in place between the 2 terminal bars. This disc is always in contact with both terminal bars at all times. There is a little indent in the disc which allows the plastic (on-off button) toggle to grip this disc and rotate it upwards ( ON) and downwards (OFF). It has a very smooth action.
Question… How does this switch function? Is it some kind of a mercury switch?
It baffles me cause that metal disc is ALWAYS making contact with both terminals; yet when the indent is rotated upwards….I have continuity…when rotated back down to OFF position…no continuity. ( which of course is how a switch is suppose to work)
Since the disk is metal and is always in contact with both terminals…what is keeping it from always being hot (ON)?
Must be a mercury switch I think, but could it be something else?
Just plain curious.
Anyone know the answer? Thanks.
Davo
Replies
Mercury switch. A very reliable design. Silent. I have driven helpers nuts by telling them the capsule is an electrical component and telling them to figure out, with meters and test equipment, what it is. Out of a few dozen helpers I only had one to get it right.
Yep, a mercury switch. I remember as a kid (mid 50's about 10 years old) when my father who was both a electrician and electrical engineer brought some of these home and installed them in our house. Neat because they didn't make any sound. Replaced old push button swithes (two buttons, one on, one off). Dad got his BSEE in 1933, no work for engineers, but got a job wiring old farm houses as REA came into central Illinois. He was both a contractor and inspector for REA. Could not inspect his own work, but did it for other contractors -- and they did it for him. This was "OK" back then. When WWII came along they wanted engineers so he sold his inventory but kept his contracting license and continued to do some wiring work for many years.
Deblacksmith