Looks like a rehash of the past., Jim, I don't disagree with what you say
regarding the saftey issues, but I do disagree on the legal and illlegal
portion. The change in the NEC for new wiring installations of combined
120/240 loads from 3 wire to 4 wire wasn't changed until the 1996 NEC and
existing 3 wire installations are still gradfathered in, unless superseded
by local ordinace. An easy google search will bring up the sections that
apply. Again I don't disagree with you other than the part about it being
illegal since 1975, that just doesn't check out in the NEC.
73's
Chuck
W6RD
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <amps@contesting.com>
Sent: Thursday, July 17, 2008 9:33 PM
Subject: [Amps] 120V Loads in 240V Power Amps
> 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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