[Amps] 4 wire 240VAC service? What to do now?

[Dick Green WC1M]

Yes, and the neutral and ground must be isolated in any subpanels as well.
However, there's one exception: if the subpanel is more than a certain
distance from the main panel (not sure how far), such that the code requires
a separate ground rod at the subpanel, the neutral and separate ground rod
are connected together in the subpanel. This could be the case for a
subpanel in a separate outbuilding.

I have this situation at my station, though not for an outbuilding. I have a
motorized crankup tower with a 120VAC motor about 270 feet from the house.
Four #10 wires buried in a 4' deep conduit (separate from the radio cables,
of course) carry 240VAC from the main panel in the house to an outdoor-rated
subpanel mounted next to the tower. The wiring and subpanel were installed
by a licensed electrician.

As I recall, the electrician did not bond neutral and ground together at the
subpanel, nor did he connect the subpanel to the tower ground. I'm sure that
I had not built the tower ground system when he installed the subpanel, and
he didn't bother to install a separate ground rod for the panel.
Essentially, the installed it like a subpanel inside a house would be
installed. 

After the subpanel went in, I built an extensive ground rod system for the
tower: 12 rods spaced 16' apart in a radial pattern from the base, cadwelded
with 1/0 wire. Several years ago, I read up on the code, and changed the
wiring at the subpanel. I don't recall exactly what I did, but I do know
that I connected the subpanel to the tower ground and bonded the local 120
VAC neutral to the tower ground in the subpanel. I believe this is correct.
What I don't remember is whether I disconnected the neutral and ground wires
coming from the house. It seems to me that they should be disconnected in
this case. In other words, ground and neutral for the 120VAC branches from
the subpanel should use the local neutral and ground, not the ones coming
from the house. Anyone care to comment on that? What would be the specific
hazard if the house ground and neutral wires are connected to the subpanel
ground and neutral, and thus to each other?

As soon as the snow melts, I'm going to take a walk to that subpanel and
refresh my memory on how it's wired!

73, Dick WC1M

-----Original Message-----
From: Jim Brown [mailto:jim at audiosystemsgroup.com] 
Sent: Monday, April 04, 2011 12:35 PM
To: amps at contesting.com
Subject: Re: [Amps] 4 wire 240VAC service? What to do now?

On 4/4/2011 8:26 AM, Commander John wrote:
> I twisted the 2 grounds together and installed them in the center pin jack
as it was that or cut one off.
> Is there a better way?

PLEASE go back and STUDY what I  and several others have written several 
times in this thread, and in the power and grounding  tutorial that's on 
my website.  http://audiosystemsgroup.com/publish.htm

NEVER, EVER, connect NEUTRAL to GROUND at any point other than the point 
where it enters the building. The proper connections to your amplifier 
are the two 240V hot wires and the green wire. The neutral must NOT be 
connected.

73, Jim K9YC