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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Topband Reflector
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