HDTV Almanac - Are You Protected?

[alfredpoor]

Last year, a transformer on an electrical pole outside our home decided to go out with a bang and in a blaze of glory, showering sparks onto the street. Pretty spectacular on its own, but even more impressive when you consider that it also took a number of innocent victims with it. I don’t know [...]

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[Roger Halstead]

I worked 26 years in Instrumentation in industry, went to college, earned a degree (BS in CS - Has a nice ring<:-)) ) and worked 7 more years before retiring as a Computer systems project manager for a large multinational chemical corporation. I worked with computers from the days when they loaded the program from paper tape after punching in the machine code monitor from the front panel buttons and they contained a 16K or 32K memory bank that looked like a bad backlash on a bait casting reel called "core memory".

Here at home I'm also an Amateur Radio Operator (Ham) with a large antenna system. The first 5 years That tower and antenna system http://www.rogerhalstead.com/ham_files/Tower29.htm took about 3 verified direct lightning strikes a year. There were two the next year and none since. The neighbors used to call it the neighborhood lightning rod. (It was a 130' to the top antennas). http://www.rogerhalstead.com/ham_files/tower40.htm

Two points. The number of strikes were visually verified so that 17 is a minimum number. Also there was no damage to the tower, antennas, or any equipment in the house. There is a very elaborate ground system for the tower, house, and shop.

Now as to the use of MOVs. Yes they can work, BUT they have limitations. Each MOV is good for only so many jouls of energy. Even a little voltage spike degrades them a little bit. Each MOV is made up of thousands of tiny metal oxide diodes. A spike exceeds the the break down voltage and the device conducts while sacrificing some of the diodes. That means the break down voltage and capacity is now just a bit lower. How much lower depends on the voltage and energy in the spike it just swallowed. Actually the device starts conducting at a given voltage and as the voltage rises it conducts more. (more diodes are conducting) It is after all a Metal Oxide Varistor or in plain language it is much like a resistor that goes down in value as the voltage goes up. IE the higher the voltage the lower the resistance and the more current that is conducted so it quickly reaches a point where the device acts as if it were a dead short across the lines. That *usually* destroys the device and hopefully protects what ever it was *supposed* to protect

The second point is the grounding of the protective strip. The best protection is a combination of what is called a "single point ground" AND a substantial protective device at the service entrance to the home. The idea of the sol called "single point ground" is to have the voltage on all electrical lines (including phone, TV, cable, and antennas ) rise and fall together whether from a voltage spike coming in on the power lines, or voltage induced from a nearby lightning strike.

I seriously doubt that any protective outlet strip, or UPS exists (for a reasonable price) that could come any where near protecting a home from the full fury of a shorted transformer. Depending on the transformer it likely was at least 12 KVA or even 24 KVA. That is a LOT of power, and far beyond the capabilities of these outlet devices. OTOH Ground Fault Detectors *might* have helped prevent a major disaster such as fire, or electrocution.

Another problem with the outlet protection is improperly installed, or installed with an inadequate ground system they can make the problem worse instead of better. This is probably one of the reasons the protective outlet strips are losing favor with computing systems.

As for lightning there is no 100% sure fire protection. The only thing you can do is improve the odds in your favor. Lightning is unpredictable and not all lightning is created equal. It varies from the standard to the super strike that even blows holes in airplanes. Fortunately the super strikes are rare.

[eliwhitney]

Morning Roger Halstead ...

I've always enjoyed reading your posts re: That most-elaborate Antennae System as well as the descriptions of the grounding of same that you've installed!!

Anymore, with all of the very small, loaded PWBs inside essentially-all of our Household Appliances, it is becoming more apparent that some sort of "Whole Electrical Service Protection Scheme is warranted?"

Locally, the Power Utility seems to have a start or proper offering, involving an installation by them of the "Collar" at / inside the glass electric meter base plus the addition of (2) copper-clad 8' long steel grounding rods 6 feet or greater apart. These are driven into Mother Earth as near that meter base as practical & bonded w/ #6 copper & the usual approved Rod Clamps, etc..

Better for the Central A-C / Dryer / Range / etc., than the 120v items .... so, they also provide an assortment of UL Approved devices as you have mentioned ... at least, now, there's a proper grounding path for the neutral of these to bleed off their "hits!"

As you eloquently-explained, essentially nothing affordable by an individual Home Owner is going to "do-the-task" of an exploding / shorted Transformer - - - but - - - ordinarily, these Protection Plans will help alleviate the damage w/ the 'little overloads."

All for a very-few $$ monthly ...{an accompanying "Insurance Policy" to pay for any Damages, too!}

eli ...{a '30' years & out Mechanical Engr that ended up the last ~ 25 yrs w/ "Ma Bell."}

[alfredpoor]

Good points, Roger. I completely agree that even a good surge protector strip is not a total guarantee of protection. At the house I mentioned, the local power company will install a serious surge protector for the whole house (and charge you monthly for it), which we did after the fact, but surprise, surprise, the warranty only covers appliances; no electronic damage is covered.

Here in the Bit Barn that we built to hold my office and lab, I had the electrician install gas discharge capacitor protectors on the electrical service where it enters the building. I am not an electrical engineer, but from what I understand, these recover from a strike unlike MOVs which get used up. In any case, I go belt-and-suspenders and have surge strips on all electronics as well (stand-by power supplies on the critical equipment).

My goal for the Almanac piece was not go for the ultimate in protection, but to get readers at least thinking about the problem and to get them to put up at least a little defense for their expensive electronics. I figure that this is a case where a less than optimal solution is still much better than doing nothing.

Alfred

[Roger Halstead]

Thanks, I appreciate the comments.

I agree that consumers need to be made aware that dangers about for their expensive equipment and they can do things to reduce the risks. They should take steps to protect their equipment (and money invested). It's not just that equipment either. In an unprotected system lightning induced voltage spikes, or even equipment induced voltage spikes can cause equipment to fail with a cascading effect causing other equipment to fail. Surprisingly electric motors as in freezers and refrigerators are quite vulnerable either directly or through their controllers. The motors themselves are also prone to damage from *low* voltage. It is possible an induced spike coming in on he TV coax could progress from an unprotected TV to take out most newer appliances in the home.

With all the electronic controls now present in furnaces, air conditioners, freezers, and refrigerators today's appliances they are much more efficient, but they are also far more vulnerable to voltage spikes than the older appliances. A year ago last summer lightning struck the transformer across the road and one house north (missed my tower). They lost almost every major appliance in the house in addition to the TV, DVR, telephone...etc.

But at-any-rate protection from voltage spikes and line voltage excursions may at times save a home owner a lot of grief and money. It's certainly worth the investment if installed properly.

[ccclvib]

After being bitten once (and I should have known better), I think I should mention the fact everyone who has a DVR also needs a UPS (Uninterruptable Power Supply) to serve it. Those hard drives are not only susceptible to voltage spikes but also to short-duration voltage loss, which the UPS also does a good job of avoiding. Since the first Dish Network DVR I had got bombed by a quick power loss, I always have had a (rather large) UPS running for all my home theater equipment. I had been using other UPS packages before that for my computer systems, which is why I say I should have known better.

[Roger Halstead]

Just don't plug a UPS into one of the protected outlet strips.

The UPS not only gives backup power, but it also protects the equipment with most of them having straight through, protected outlets in addition to the ones that have backup power (which are also protected)

[Richard]

If anybody is looking for an in depth detailed discussion on this topic...

AC Surge/Lightning Suppressors
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