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Re: [TowerTalk] SurgeGuard?

Subject: Re: [TowerTalk] SurgeGuard?
From: Jim Lux <>
Date: Mon, 09 Jan 2012 17:26:35 -0800
List-post: <">>
On 1/9/12 1:53 PM, Jim Miller wrote:
> Anyone have experience with the SurgeGuard?
> It installs as a shim under the
> power meter to provide whole house protection.
> The company claims protection for "sturdy white goods". I take that to be
> something motor driven. They specifically don't cover semiconductor devices
> although BGE Home offers a $10K insurance when these are installed which
> covers TVs, etc.

Sturdy white goods?  Interesting turn of phrase.. Sturdy appliances 
don't need much in the way of surge protection.  A number of studies 
have shown that most household appliances can take 1-2 kV spikes that 
are short without too much trouble.  The transformer in the usual 
wall-wart, for instance, provides common mode isolation, and has enough 
inductance that differential mode spikes don't get through.  (although, 
there's the whole interwinding capacitance thing...)  Anyway..

The big problem is what's called "swell": a relatively long duration 
higher than normal voltage, which basically cooks any MOV that has too 
aggressively low threshold voltage.  And of course, the cheap surge 
protectors have low voltages because that sounds good to the customer 
(ours clamps at 140V unlike those inferior 170V clamps)

If you have a problem with the neutral in the feeder (not all that 
uncommon, as it happens) you could easily wind up with a slight 
overvoltage on one side or the other, just enough to get those MOVs nice 
and hot.

In any case, this form factor (under the meter) is a very popular one 
these days.  It's easy to install, doesn't require wiring anything, etc.

google/bing for "Leviton 50240" for a typical unit.  they've got the 
datasheet there.  Takes a 20kA nominal discharge current, clamping at 
600/500/400V  (not sure why L1-N is more than L2-N... L-L is 400V)

You need to have a decent ground (not RF ground.. just reasonably low 
impedance) to give the common mode transients somewhere to go. 
presumably, your neutral is bonded to ground at the service entrance 
(and ONLY at the service entrance)

(something a bit more burly would be a Leviton 42120-1, but that's not a 
meter base style.. but it does have filtering built in)


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