Mike,
An excellent question and its one I wrestled with painfully when connecting my
Alpha 77Dx to service in my new home....
Most amateur amplifiers do not require a neutral when configured for 240VAC
service. The sole purpose of the neutral in these
applications is to adequately carry 120 VAC current: In the case of the Alpha
77, 77Dx/Sx, 70A, and 70V it is only the blower that
requires 120 VAC irrespective of the 120/240 tap configuration in the amp.
That blower always needs to see 120 VAC and it is not
transformer tap-dependant. I suspect your Henry is wired in a similar way.
This requires four wires: LINE-NEUTRAL-GROUND-LINE
service. Remember, current should only flow through a neutral...never a
ground. The Alpha manual suggests that tying the neutral
and ground together at the amp is allowable. Back in 1970, perhaps it
was....but as you'll see, its a safety hazard.
While its true that the US wiring standard calls for the neutral and ground to
be tied together, this is ONLY allowed at one point:
the service distribution panel. Neutral and ground should never come together
anywhere else in the electrical network. Why? If a
neutral fault occurs (e.g., opens up) at the equipment end, current now flows
through the ground wire (because neutral and ground
are tied together at the panel), causing your BNC connectors, SO-239, RCA
connectors and any other grounded connector on the back of
your amplifier to conduct current for the 120 VAC demand; and thus the
amplifier case has now become hot. If the blower had the
ability to adapt 240 VAC through changeable taps as is the case in most amps,
this would not be a problem and the required service
would be LINE-GROUND-LINE....and no neutral.
My solution and in my opinion, the ONLY correct solution for these amps is to
run four-wire service to the panel. I used a 30A
4-wire Hubbell Twist-Lock connector and was purchased from Home Depot.
Fortunately, this change required no mods to the Alpha amp.
To my surprise, Alpha tied neutral and ground together at the Cinch-Jones power
plug. I simply cut the jumper on the power cord
plug.
-Paul, W9AC
----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: "AMPS" <amps@contesting.com>
Sent: Wednesday, December 11, 2002 10:43 PM
Subject: [Amps] Neutral vs Ground Connection for 220 VAC
> Hi All,
>
> Our club just inherited a Henry 2K-D which I was planning to
> wire for the 220VAC service that we have available in the
> shack. My quandry is how to properly connect the 4 wire
> 220VAC wiring on the Henry (2-hot, 1-neutral, and 1-ground)
> to the 3 pole 220 outlets in the shack? While its clear to me
> that tying the neutral and the safety ground connnections on
> the Henry together will work functionally, I am wondering if
> this would be kosher from a safety/code point of view. Is
> the third wire in a 3 prong 220 outlet supposed to be a safety
> ground or is it actually allowed to carry neutral current in the
> case where both 110V and 220V are needed inside the box
> (it looks like the pilot bulbs and blower in the Henry use one
> "phase" of the 220V circuit to get 110VAC)?
>
> Thanks,
>
> Mike, W4EF..................
>
>
>
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