If a sub panel is fed from a breaker in the main panel then it is a sub
panel.
A sub panel doesn't have to have a main breaker in it.
Yes neutral remains ungrounded at the sub panel.
YES you DO need the equipment ground wire from the house to the sub panel!
This requires 4 wires from the main panel to the sub panel.
If the sub panel is in a separate building from where the main panel is, you
also need local ground rods at the sub panel in addition to the ground wire
from the main panel.
You must ALWAYS, ALWAYS have a wire path from your equipment ground back to
the panel where the main breaker is. This is the only way a breaker will
trip if there is a fault to ground (chassis).
You can not depend on any earth connection to trip a breaker!
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of James R Carr
> Sent: Monday, April 04, 2011 3:14 PM
> To: Dick Green WC1M; jim@audiosystemsgroup.com; amps@contesting.com
> Subject: Re: [Amps] 4 wire 240VAC service? What to do now?
>
> It should be treated as a seperate building. The panel would have it's
> own
> main breaker but the neutral would remain ungrouned and the panel
> enclosure
> and equipment ground would be grounded to the seperate ground rods. The
> neutral is normaly only grounded at the service main. The neutral is
> coming
> from the center tap of the 240 volt winding on the pole pig and you need
> that to develope 120 volts. You can never use a ground as a current
> carrying
> conductor. You don't need the equipment ground from the house as you are
> establishing it at the tower. It's sole purpose is to trip the breaker
> in
> the event of a ground fault and keep all the metal enclosures etc at a
> ground potential.
> Jim
> N7FCF
> ----- Original Message -----
> From: "Dick Green WC1M" <wc1m73@gmail.com>
> To: <jim@audiosystemsgroup.com>; <amps@contesting.com>
> Sent: Monday, April 04, 2011 10:49 AM
> Subject: Re: [Amps] 4 wire 240VAC service? What to do now?
>
>
> > 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@audiosystemsgroup.com]
> > Sent: Monday, April 04, 2011 12:35 PM
> > To: amps@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
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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