Topband: Best Outlet sttrip

[Paul Christensen]

Tom,

You have probably already seen references like this:

http://www.zerosurge.com/technical-info/how-surge-suppression-works/

One can either believe it, or dismiss it as voodoo engineering.  I'll not 
try and persuade its use other than to point out that if a whole-house SPD 
is installed at the power meter or entrance panel, and if its clamping 
devices are working without failure, then there's probably no need for 
additional SPDs anywhere else on a branch circuit.  But if that protective 
entry device does fail, and I'm left with only secondary SPD protection on a 
branch circuit, I would rather clamp to neutral where it's still at ground 
potential by virtue of the neutral-to-ground bond at the entrance, but not 
potentially raise the potential of the branch circuit's grounding 
conductors.

Paul, W9AC

----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: "Paul Christensen" <w9ac at arrl.net>; "TopBand" <topband at contesting.com>
Sent: Wednesday, October 09, 2013 3:01 PM
Subject: Re: Topband: Best Outlet sttrip


>> 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.
>
> Paul,
>
> The issue I have with this  is ***thinking*** ( incorrectly) that unwanted 
> surge is on the hot or neutral, and is diverted to the safety ground 
> because we call that "ground". That's a big stretch, and probably mostly 
> never true. The suppressor doesn't pluck something off a hot lead and drop 
> it there just because we call it "ground", or because we want it all to be 
> collected and go there.
>
> A suppressor only clamps or limits voltage across its terminals. It goes 
> low resistance where a transient comes along. I can have two suppressors, 
> one each from hot and neutral to safety ground (although that is a poorly 
> thought-out system) and it will simply clamp the three wire ends together. 
> It does not back-feed the safety ground or neutral with any grossly 
> upsetting currents, because almost certainly any **power line** sourced 
> surge already came from the direction of the breaker panel. The clamps 
> would divide currents by wire impedance and clamping voltage differential, 
> so the neutral and other two wires would be part of it any way we wire the 
> clamping system.
>
> To illustrate how misplaced the concept of protection devices increasing 
> damage actually is, the safety ground is already connected to the chassis! 
> It is a thinner bare wire that closely parallels the other two wires for 
> some significant distance, and already connects to the neutral at the box. 
> Suddenly we are supposed to believe that clamping it to wires it already 
> parallels (and already has a low impedance to) will cause or increase 
> damage. Additionally, there is a bunch of stuff inside devices that lowers 
> impedance or voltage breakdown between all conductors anyway.
>
> There isn't anything wrong with clamping the lines at a common point in 
> the shack, or at any equipment cluster, no matter what else we have in the 
> system.
>
> Most of the damage we get is common mode from our antenna grounds and 
> antennas. The potential from that sees a voltage differential from the 
> mains. That differential already occurs between the antenna and chassis 
> common connection to all three wires almost equally. If you DON'T have the 
> MOV  device, the safety ground and chassis is actually the best path to 
> the box. After all, that safety ground already is directly tied to the 
> chassis, and to out antennas, or in consumer gear to Telco lines or CATV 
> lines.  The only thing the MOV's do for nearly all of the problems is keep 
> the "snap" out of the power line wiring and components inside the 
> cabinets.
>
> I'm just baffled why any theory would propose allowing two wires of a 
> three wire line float from the chassis is an improvement, when the bulk of 
> the problem is a ground loop from the antennas or cable/Telco grounds to 
> the power mains, and most mains surges are the same. A secondary but 
> lesser mains issue would be between the neutral and hot, and that surge 
> would primarily flow back on the heavier neutral rather than the lighter 
> safety.
>
> This entire thing defies common sense. The next thing I expect to hear is 
> them telling us to cut the safety ground off to protect their ports.
>
> 73 Tom