Surge protection specifications

[JHZR2]

I'm following up about surge protection. Got some info from Tripp Lite tech support.

Apparently Belkin uses an "additive" approach at giving the joule rating that they publicize. A 918J Belkin protector protects at 306 J for L-N, 306 J for L-G, and 306 J for G-N. So really it protects at 306J but they claim all summed up for advertising purposes.

I emailed Tripp Lite as it wasn't as clear. But the number they give is a per line valuation.

So Tripp Lite might sell a 518J protector and Belkin sell a 918J protector. But the Tripp Lite unit protects at that lever per line pair ( 1554 J in Belkin speak), while the Belkin net protection per line pair is 306J.

Hope that makes sense. My take away is to not trust claims of any companies...

 

[webfors]

Amen... marketing is evil.

FYI, my belkin UPS was pure junk, especially the software it came with. Back to APC and happy again.

 

[MolaKule]

If you want good surge protection, install one at the breaker panel.

The one I use is Intermatic Panel Guard.

 

[JHZR2]

Originally Posted By: webfors
Amen... marketing is evil.


Agreed. That's why I thought this was worthy of it's own thread...

 

[jaj]

If you sidestep the marketing (which in my view is highly questionable because most suppression products don't actually provide any value at all) and look at it as an engineering issue, you end up in a totally different place.

The truth is that most exterior surges (lightning, grid transients, etc) are simply too energetic to be suppressed by a consumer surge suppressor.

The surge suppressor's job is not to absorb the surge; it's to absorb the surge long enough to blow the first upstream branch circuit breaker or local fuse and open the circuit. Surge suppressors require an over-voltage condition to make them kick in, so let's say that your 1000 Joule suppressor kicks in at 250 volts (peak line voltage is 170 and you need some headroom). The source impedance at your living room wall plug limits the current to about 5000 amps into a dead short, so the 1000 Joule suppressor is swallowing 1,250,000 Joules per second. It'll last exactly 1/1250th of a second, or 800 microseconds before it overheats and goes open-circuit, ending an illustrious career. Sadly, thermal circuit breakers take twenty times that long to open. Most Bussman-style fuses won't respond that fast either, unless they're really small, like instrument fuses.

My point is that your feeling of safety from most consumer suppressors is an illusion. The most important part of getting good surge suppression for real is the quality of the ground at the service entrance. The ground rod needs to go deep enough to be wet with ground water, or you need a damp field. It's your real protection. The neutral has to be tied to ground with a heavy link at the entrance, as most electrical codes call for. The real suppression that protects your house or business is the stuff the utilities put on poles and in the underground cableways, and it can only do its job if you've got proper grounding at the panel.

 

[JHZR2]

Good stuff... If the unit goes open circuit, isn't it inherently protecting the connected load?

 

[jaj]

The typical commercial surge suppressor consists of an outlet strip, a set of varistors across the LN, LG and GN wires, and a pop-up breaker. The breaker is in series with the loads and the varistors are in parallel with the load. When a surge arrives, the varistor switches from non-conducting to conducting and swallows (for lack of a better term) the surge. If it can do this long enough, the pop-up breaker will open.

However, if the varistor goes open circuit before the breaker opens, then it stops protecting the load. At that point, the protected load itself will usually fail and that will blow the fuse or breaker.

 

[jaj]

There is another type of transient that these suppressors can suppress, and that's the kind that happens when your next door neighbor (or you) strike an arc with your welder and the welder just happens to be on the same leg of the distribution transformer that your load is on. That crackling connnection creates "spatter" in the electrical circuits, high voltage and high frequency transients that look like hair on an oscilloscope.

A simple suppressor like the ones we're talking about will clip those spikes at 250 volts, and they're short enough that the varistor survives without any damage. However, suppressing that kind of noise is more a job for an EMI/RFI suppressor like a Corcom than it is for a surge suppressor. These spikes have rise and fall times in the nanoseconds, and they pretty much surf the connection wiring, behaving as radio waves to get around barriers set up to stop them. Most consumer electronics are well shielded and protected internally from this kind of interference. If they weren't, they just wouldn't stay sold.

 

[daves66nova]

Is this an alright one for a comp,lcd tv and a cheap, 20 y.o. stereo setup?
http://www.ebay.com/itm/320814520783?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649