Several months ago, we had a discussion about what was a proper
way to connect a 120V load to a 240V source. Since about 1975, it
has been illegal to connect a load between either side of the 240V
line and GROUND. In North America, it is both unsafe and a
violation of electrical codes to cause more than 5 mA to flow on
the ground conductor (the green wire). Load currents are permitted
ONLY on the phase (hot) conductors and the neutral. A 3-wire 240V
outlet has only the two phases and ground.
A few weeks ago, I was helping a local ham troubleshoot a hum and
buzz problem in his multi-multi station. One of his power amps is
an Alpha 77. I measured 550 mA on the green wire. The cause is a
120V fan connected between a phase and ground. This may have been
legal when the amp was built (c.a. 1972), but it has not been
legal for at least two decades.
I recently described this as a potential source of hum and buzz in
transmitted audio in a presentation to our ham club (NCCC). A
"right" and "wrong" way to connect a fan is shown on pages 38 and
39 of http://audiosystemsgroup.com/HamInterfacing.pdf. Depending
on how an individual amp is built, it could be quite easy to
rewire the fan to eliminate the problem. The "right" circuit is
similar to what is done on the TenTec 425 Titan (the Titan has an
additional buck/boost secondary winding to vary the fan speed).
73,
Jim Brown K9YC
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