Topband: Best Outlet sttrip

[Paul Christensen]

> "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 at arrl.net>
To: "TopBand" <topband at 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
>
>
>
>
> _________________
> Topband Reflector