Rehash for sure, this subject comes up regularly.
Even some home appliances such as dryers were wired that way in the past.
Ive yet to hear of a fried homeowners lawsuit.
The Alpha 77 mentioned isnt the only vintage amp wired that way either.
Potentially unsafe, yes. Grandfathered, yes.
Carl
KM1H
----- Original Message -----
From: "Chuck & Vicki Tifft" <cftifft@sbcglobal.net>
To: "Jim Brown" <jim@audiosystemsgroup.com>
Cc: "Amps Reflector" <amps@contesting.com>
Sent: Friday, July 18, 2008 2:26 PM
Subject: Re: [Amps] 120V Loads in 240V Power Amps
> 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 existing 3 wire installations are still gradfathered in, unless superseded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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