I never use a wrench which has exposed metal surfaces long enough to short
a battery, and I always disconnect the negative terminal (- ground assumed here) and cap it before working around them. Al WA6VNN -------------------------------- Disconnecting power before working on the gear to remove/replace parts is basic to both low and high voltage supplies. My one up-close and frightening experience with low-voltage high-current supply shorts occurred on an F-86 (Korean war era jet fighter) flight line at Lockheed. It was the middle of the night and bitterly cold as I and another tech worked on two fighters sitting side-by-side. They were powered by ground carts. We had lowered the canopies almost all the way down to conserve a little heat in the frigid cockpits as we ran through the avionics ground checks. Suddenly I heard one of the power carts groan under heavy load. It caused me to look up and out of the cockpit to see what was going on. The plane next to me had smoke billowing from the cockpit, coming out around the almost-closed canopy. I could see the other tech's head lying against the canopy. He was apparently unconscious. I hit the canopy button and clambered out as it slowly wound open, yelling for help, very conscious that these planes were fully-fueled bombs sitting wingtip to wingtip waiting for a fire to set them off. We got the guy out. He was splattered with burns but the plane wasn't on fire. Later we learned that he had discovered a defective circuit breaker. He had a replacement with him, but decided he didn't want to open the canopy and climb down to disconnect the power cart. The circuit breaker connected to power by a wire with a lug on the end that attached with a screw into a threaded hole in a large copper bus bar. As he was turning the screw, he dropped the screwdriver and it fell touching the power bus bar and the aluminum side of the console. He got a face full molten metal blobs as the shaft of the tool literally exploded in his face. He instinctively stood bolt upright in the cockpit, smashing his head against the closed canopy and knocking himself unconscious. Lockheed management and the US Air Force were not impressed. They had a badly damaged jet fighter with molten metal drooled down the side of the console and cockpit and it could have been much, much worse. I think he found a new line of work. Even "minor" short circuits can cause lots of grief. It's very easy to instantly fry a PC board trace with a temporary short circuit. Those can usually be fixed (once you find the break), but it's still a very unnecessary and easily avoided damage by following simple safety protocols, including removing power before touching the circuit to remove parts or taking any other short-cuts. And for those of us who regularly work around equipment with high voltages - a few hundred volts and up - allowing ourselves to be lulled into complacent behavior by the low voltages in most gear today can be dangerous. One time I was troubleshooting a receiver that had something that smelled hot so I was gingerly touching resistors to see if one was overheating when I suddenly remembered I was working on a tube-type receiver with a 250V supply! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
