"First, in most NA power systems, neutral and ground are connected at only
two places: (1) the secondary of the utility company's transformer; and (2)
at the premises main panel board."
Sorry, should have read "...neutral and ground are connected *together* at
only two places..."
Paul, W9AC
----- Original Message -----
From: "Paul Christensen" <w9ac@arrl.net>
To: "TopBand" <topband@contesting.com>
Sent: Wednesday, October 09, 2013 9:55 AM
Subject: Re: Topband: Best Outlet sttrip
I'm afraid I don't understand how a surge
protector that clips an, e.g., 1KV spike on a 120 VAC line can end up
doing more damage than no protection all. I understand that the
clipped current pulse returns through the ground line and will cause a
voltage spike on the ground, and I also understand that other
interconnected equipment connected to different grounds may
potentially see part of the spike, but on balance that seems to me to
be a less dire situation than having no protection at all.
I think it comes down to the surge protection device (SPD) wiring
configuration in relation to its placement in the electrical system.
First, in most NA power systems, neutral and ground are connected at only
two places: (1) the secondary of the utility company's transformer; and
(2) at the premises main panel board. An SPD, if used, should first be
placed at either the electric meter or panel board so that surge currents
near the utility entrance may divert on a short path to ground/neutral.
On a branch circuit, the problem potentially becomes worse the further the
distance of a common secondary SPD from the main panel (so-called "3 modes
of protection" from devices using three MOVs). Surge currents being
induced from say...a shack entry point can divert a large current onto the
grounding conductor, causing a large voltage differential to other
grounding points on the same branch circuit. On a branch circuit, surge
current should never be diverted to a grounding conductor. It may be
safely diverted to the neutral conductor and even then, it's best managed
if at least a portion of the surge potential can first be stored and then
"bled" onto the neutral where that neutral is connected to ground at the
main panel. Common secondary protection SPDs meant for use on branch
circuits don't meet this requirement, despite IEEE's recommendation that
common "3 modes of protection" are safe for use on a branch circuit.
Secondary SPDs that do accomplish this goal are made by BrickWall,
ZeroSurge, and SurgeX.
In a nutshell, my recommendation (for what little it's worth) is this:
(1) a secondary SPD on a branch circuit should only be used when a primary
SPD is used at the utility company's meter or at the premises main panel;
and (2) assuming condition 1 is met, then the secondary SPD should divert
surge current only onto the neutral, and never the grounding conductor.
Finally, on the issue of balanced audio: it costs manufacturers of
consumer electronics and ham gear no more to balance all audio inputs with
a "3-stage" instrumentation op-amp circuit. It's far more important to
balance each input this way than to balance audio outputs although
balanced outputs are preferred for best system matching, especially on
long cable runs or where distribution is complex (e.g., a broadcast or
recording studio with cross-point switchers). With a true instrumentation
input, the input circuit does not care if the source is balanced or
unbalanced. It's simply a two terminal, floating device with extremely
high common-mode rejection (CMRR) performance. The best laid out
instrumentation circuits carry that high rejection well into the HF range.
Paul, W9AC
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