Jim, just verifying my understanding of the following;
Green (Grounded) and White (Neutral) bond ONLY at the MDP (Main Distribution
Panel). Green wire must run with neutral to main or supplemental panel and
MAY also be grounded elsewhere but those grounding points MUST be bonded to
the system / site / premise ground in accordance with the National
Electrical Code.
73 ES DX,
Gary -- AB9M
-----Original Message-----
From: Jim Brown
Sent: Thursday, September 06, 2012 4:38 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Station power supply??
On 9/6/2012 1:12 PM, Don Allen wrote:
A quick question: Is it best to connect equipment together from chassis
to chassis, or from each individual chassis to a single point ground? I
was taught it's best to connect each to a single point ground point, e.g.
to a copper buss bar behind a shelf. And, should it be a short fat copper
wire, or short wide copper strap? The latter is certainly better for an RF
ground.
The advantage of wide braid or wide copper strap is SLIGHTLY lower
inductance, and slightly reduced resistance due to skin effect. At power
frequencies, it's all Ohm's Law -- conductor cross sectional area and
conductivity (that is, copper as opposed to steel or aluminum) are all
that matter. Braid is good INDOORS, but exposed braid oxidizes quickly
outdoors.
Star or chassis to chassis? For hum/buzz, what matters is DC resistance
between boxes having unbalanced baseband connections between them
(audio, RS232), so short fat copper between them is best. From an RF
point of view, as long as those connections are all very short and the
combination of them (or the chassis of the transmitter) are well bonded
to ground, there's no significant difference between this and the
so-called star.
The most important part of ANY grounding scheme is that ALL GROUNDS MUST
BE BONDED TOGETHER, and by the shortest practical path. That means
power system, CATV, telephone entry, satellite dish, lightning
arrestors, ham antennas, ham shack. The fundamental intent of all of
this is that in the event of a strike, every part of the system rises by
the same voltage.
One set of bonds is the Green Wires that run from the main breaker panel
to all outlets, and are bonded both to Neutral and to earth at that
panel. That takes care of both protecting personnel and property from
an electrical fault in a piece of connected equipment, and also limits
the amount of voltage that is induced in power wiring in the event of a
strike. It also limits the voltage between Neutral and Green. An
important function of the Green wire is to cause a fuse or breaker to
blow in the event of an equipment fault.
The NEC DOES call for proper grounding of antennas, but it's not in the
part of the NEC that most folks read.
73, Jim K9YC
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