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Re: Topband: Best Outlet sttrip

To: "TopBand" <topband@contesting.com>
Subject: Re: Topband: Best Outlet sttrip
From: "Paul Christensen" <w9ac@arrl.net>
Date: Wed, 9 Oct 2013 09:55:52 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
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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