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Don't become a statistic
This next incident was the kind of thing that could happen to anyone, but should not, if all safety rules are followed.
WKYC, 1100kHz 50kW Cleveland, OH, had been sold to WWWE, which was running the original 100kW Westinghouse transmitter minus one modulator and one power amplifier tube at 50kW while waiting for a new transmitter.
One morning the phone rang in my office and Charlie said, “John, we've got no audio”. At that time we were operating WWWE with local manual transmitter control. I verified that audio was leaving the studio and Charlie, the transmitter engineer, confirmed it was reaching the transmitter. He opined that it was the modulation transformer. I told him I would be right out and to check connections and overall operation, but not to open the transmitter until I got there. I always insisted on two men when working on a transmitter.
About 10 minutes later, I arrived, assessed the situation and agreed that it probably was the modulation transformer. We switched off the transmitter and heard the usual clatter as safety-shorting connections, killed the transmitter high-voltage bus and went to the 25-square-foot high-voltage room. I was carrying the grounding stick and as we opened the door I heard another grounding safety drop into place.
We approached the modulation transformer, which was several feet high with a large four-microfarad capacitor mounted on it. Charlie pointed out the connections to the primary and said, “It looks as though there is corrosion, I bet that's the problem.” He proceeded to reach out his hand toward it. I frantically hit the connector with the grounding stick and yelled, “Don't touch it!
There was a blinding flash and a deafening bang as the four-microfarad capacitor, hooked to the top of the modulation transformer, discharged 11kV through the grounding stick instead of Charlie. He turned white.
This near fatality showed the tremendous importance of following standard safety procedures, which include hanging a grounding stick on equipment where work is performed. Charlie went by the sounds of grounding contacts going into place when the transmitter was turned off, and he placed his confidence in the completeness of the high-voltage grounding procedures. He didn't remember that when some components and circuits fail, other capacitors and circuits could be left energized because of incomplete grounding.
The best way to become an old experienced engineer is to assume that every circuit is hot until it is grounded at both ends.
E-mail Battison at email@example.com.
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