Need to throw my "old school" knowledge in here. It so distresses me to see all this "new fangled" stuff mentioned. [We] had archaic overhead bridge cranes, the control contacts referred to as "street car" controllers. The power contactors were rated NEMA Size 1 up to NEMA Size 5, about the size of a silver dollar. DC, 280 Volt most of it. We occasionally had trouble with AC contacts on motor starters. NEMA Size 1 and smaller. Just replaced the contacts if they were burnt. High voltage stuff mostly had fuse jacks or oil starters. But that for the high horse power 2300 and 4160 volt equipment.
Electricians carried a coarse half round file and a rubber commutator cleaner to dress contacts. Sandpaper was
NEVER used, it left grains of sand in the copper. And sometimes
conductive grains if you happened to grab a piece of emery cloth. An Isopropyl based contact cleaner if it was handy. Compressed air otherwise, but watch out for moisture.
For instrumentation contacts and relays, I usually used heavy typewriter paper or a dollar bill. Currency paper is a better abrasive than typewriter paper. In later years(early 80s), I was working on a hard drive at Majuro, in the Marshall Islands. Old style hard drive, by CDC, 18x36x30 inches or so. A 9 platter 18 head back-up drive. Had a faulty motor starter relay. I showed the "system administrator" how to dress the contacts. All I had handy was a US $100 note, traveling money. I told him a $10 would work, just not as well. He took me serious, went looking for a $100 note to
keep in the office. I laughed all the way to Ponape, my next stop.
A final note, always use an Isopropyl contact cleaner,
never "Trichloro-
anything". It will melt plastics. Won't hurt bakelite on old equipment, but will melt even high tech plastics. BTW, Vaseline won't catch fire, but it does attract/hold grit. Not a good move.
Bill Hudson
