[Boatanchors] 3 Wire line cords, again. shorted switch

[Gary Schafer]

For any of the none believers left out there about converting to 3 wire 
line cords here is what I discovered last night:

Working on an old HP 410B vtvm, had the power switch short to ground!

Yes it shorted to chassis ground. The meter fortunately had a 3 wire 
cord on it so it popped the house circuit breaker. Had it not had a 3 
wire cord the chassis would have been hot with 120 volts! The fuse in 
the meter is wired after the power switch so it never opened the fuse.

The switch had shorted to ground when I turned the switch off. It had 
worked fine while working on it.

This is an old project that I had worked on about a year or so ago and 
found I needed some parts for it. I now remember that it would 
intermittently pop the house breaker and I could never find the problem. 
Well I thought I found it one time as I had thought the line bypass caps 
had a problem. I had clipped them out and it worked ok back then.

The switch apparently would short to ground sometimes and then be ok 
other times. This time it stayed shorted and the problem was easily 
discovered.

The switch is a good quality enclosed switch attached to the back of the 
mode switch on the meter. Typical of many pieces of equipment.

Incidentally the breaker in the house is a gfi unit so it tripped 
quickly with no fireworks in the switch. Just a small pop.

73
Gary  K4FMX