Not many engineers or technicians, as a percentage, work around
high voltage with any regularity. The hazards associated with sources
capable of being able to "reach out and touch someone," as the old Bell
Telephone company commercial used to say. When an arc of voltage is
caused to "reach out and just say, 'Hi,'" the greeting can be quite
painful, damaging, or even lethal. I have experienced high voltage's
awesome ability to bite while operating unawares inside electronic equipment,
and I have witnessed other people's reactions to a surprise "Hi."
day I arrived at my permanent duty station at Robins AFB, in Georgia,
following eight months of technical school for ground-based airport
surveillance and precision approach radar, the guy who was to be my
trainer had visited the base hospital to have his finger treated for
a high voltage burn received while performing routine maintenance on
a CRT supply chassis. If I remember correctly, he was removing a voltmeter
probe from a test point on the front panel and had his finger too close
to the metal tip. It was a good introduction for me regarding regarding
the dangers of high voltages.
Our radar system had two high
power transmitters - one at S-band and one at X-band. Sticking your
bare arm inside the some portions of the equipment rack would cause
the hairs to stand on end. USAF technical manuals stipulated that removable
chassis be removed from the rack and patched in with cables for any
alignment procedures with variable capacitors, inductors, and resistors
that could not be easily accessed through a hinged front panel door.
Everybody, without exception, was taught how to blindly walk his fingers
across the tops of components (including very hot vacuum tube shields)
to reach adjustments deep in the bowels of the chassis in order to fine
tune performance in ways not possible just from the front panel. One
example that comes to mind is the ground clutter cancellation circuit,
where careful tweaking could "disappear" trees and buildings while clearly
painting a little Cessna T-33 jet trainer on final approach.
Robert Johnson issues a sage caveat on the subject in his recent Sherlock
Ohms contribution. Mr. Johnson spent a career designing high power RF
amplifiers and developed a healthy (literally) respect for the penchant
for differences of potential to attempt to neutralize themselves. He
mentions a great little safety tool that is simple to make and use to
safeguard your being.