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Author Topic: Lightning Protection For The Home?  (Read 1852 times)
N3HKN
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« on: October 24, 2012, 07:11:45 PM »

The lightning rod we call an antenna has been well reviewed. However, there are other paths for lightning to do damage to transceivers, computers and TVs. I need some advice not on the antenna area but power-line protection. Specifically are power strips, with built-in protection, effective? Are whole house protection any more effective? Any specific product recommendations?
Thanks Dick  N3HKN
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K6AER
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« Reply #1 on: October 24, 2012, 08:28:38 PM »

Please go to the Polyphaser web site and do some homework and then post your questions.
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KA4POL
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« Reply #2 on: October 24, 2012, 10:07:31 PM »

Or get the ARRL Handbook and/or Antenna book.
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W8JI
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« Reply #3 on: October 25, 2012, 07:32:28 AM »

The lightning rod we call an antenna has been well reviewed. However, there are other paths for lightning to do damage to transceivers, computers and TVs. I need some advice not on the antenna area but power-line protection. Specifically are power strips, with built-in protection, effective? Are whole house protection any more effective? Any specific product recommendations?
Thanks Dick  N3HKN


Read some of this and page links:

http://www.w8ji.com/lightning.htm

Especially this, which also applies to lightning:

http://www.w8ji.com/consumer_equipment_rfi.htm
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KD0REQ
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« Reply #4 on: October 25, 2012, 12:16:18 PM »

direct lightning strikes on a powerline will explode "pole pig" transformers.  I saw two flamed by a strike once driving by the U as it happened.  wakes you up.

so protection from a direct strike?  nope.  not within a house.

protection from a nearby surge (induced overvoltage) can be had by taking the first two positions on the breaker panel into a surge protector through the recommended breakers.  power utilities used to push whole-house protection by installing varistor packs inside the meter cabinet, but not any more.

were you to get a licensed electrician to install arc-overs on an intermediate pole between the utility drop and your service mast, down to a fantastic ground mat, and then install smaller arc-overs at the mast itself, beef up the house ground by a factor of four or so over code recommendations, and then surge at the panel and at each sensitive device, you might have a fighting chance.

even broadcast stations sometimes get the finals roached and the RF cabinet scorched by tower strikes, despite everything there being ground except the inner conductor of the hardline, and despite stout protection at the phasers for the antenna pattern.  at my telco, if there is lightning in the area, nobody works on The Frame or in the cable spreader room by order.  doesn't matter if there's a nuclear war in progress, you stay teh hell out of the frame, spreader, and coil rooms.
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AA4PB
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« Reply #5 on: October 25, 2012, 12:43:15 PM »

"Specifically are power strips, with built-in protection, effective?"

They aren't particularly effective. Most have MOVs that attempt to shunt the surge over to the grounding conductor but it can be a long run back through the panel box before it gets to any Earth ground. A whole house surge protector along with a properly installed single-point grounding system that protects ALL service lines coming into the house would be much more effective.

Most residential damage doesn't occur due to a direct lightning strike to the house or entrance wires. Most damage is caused by currents induced into the wiring (like a transformer secondary) when lightning strike a tree or some other more distant object and current flows to ground. The induced currents often find other paths to ground inside the home, through appliances and other devices. This is why a single-point ground system is so effective - it eliminates the multiple paths.
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K0IZ
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« Reply #6 on: October 25, 2012, 05:47:54 PM »

I second the above recommendation re whole house (ie service panel) device.  Several types, but one common one plugs in like a two-phase circuit breaker.   
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W8JI
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« Reply #7 on: October 27, 2012, 06:01:26 AM »

There is significant inaccurate advice here. It is common advice, but is not accurate. The advice to use a whole house suppressor can help minor surges from distant strikes or other power system problems, but is actually LESS likely to result in good local lightning protection (which is more likely to damage something).

The way it actually works is:

1.) Lightning does NOT need to be shunted to ground to protect something.

2.) Suppressors at the equipment can be VERY effective, and are significantly more likely to be effective than a whole house suppressor.

The goal of a suppressor, be it for RFI or lightning, is to have all cables or conductors entering a zone to enter at the same potential.  To be most effective the protected zone has to be small, or it has to be a closed zone.

It is nearly impossible to enclose an entire HOUSE, although a halo ground (perimeter ground) helps.

It is generally very easy and effective to enclose or group specific equipment clusters, such as a TV/DVR/ stereo center.

Most lightning damage is from common mode currents, not differential voltages between wires in a bundle.

My house had a silly whole-house suppressor on my mains when I moved in. What that suppressor did was limit DIFFERENTIAL surges to a certain voltage.  I was told this was installed because of well pump failures. They said they still had well pump failures.  :-)

This makes sense, since lightning striking a power line would follow the wires in common mode into the house, and clamping them differential mode wouldn't do a single thing for that. It would still follow the wires to or from the well.

The power company service man, when he came to change my drop, asked if I just wanted the whole house thing removed. Even the power company's own employee said the whole house suppressor didn't do much.

If you want to protect things, everything entering the house should enter at ONE point or be bonded to one point. Things off by themselves, like a TV set, should have a LOCAL protector at the device that ties the antenna cable to the mains wiring.

They make outlet strips that do this. Outlet strips that connect phone, CATV, and power mains to a common connection through surge suppressors are readily available, and they are probably hundreds of times more effective than some suppressor thing at the mains entrance. They also do NOT require a ground (more often than not a local independent ground at a device actually makes things worse).

73 Tom
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AA4PB
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« Reply #8 on: October 27, 2012, 07:13:45 AM »

The typical power strip surge protector has an MOV from hot to gnd and neutral to gnd. If a common mode spike occurs the MOV will conduct to gnd. Now the only gnd connection is normally maybe 100 to 150 feet of #12 or #14 wire back to the panel. That much gnd wire has a fair amount of resistance which causes the voltage at the gnd connection at the surge protector to rise when heavy surge current flows in it. Now if the device connected to the surge protector has any other gnd connections, like an antenna connection, then surge current may flow through the device into these other gnd paths. The result is that, as normally used, these surge protectors are pretty worthless, except for very small surges.

Good lightning protection provides a low impedance path BACK TO EARTH GROUND that doesn't flow through any of the protected equipment. That's the purpose of the "single point ground" at the entrance point. Lightning will always try to find its way back to the Earth. If you don't provide a path then it will find one which may flow through sensitive electronic equipment or, in worst case, through building materials that may ignite. Lightning current, like all electric current, divides among parallel paths in proportion to their or impedance (Ohms law).


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K8AXW
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« Reply #9 on: October 27, 2012, 08:45:21 AM »

W8JI: I've read where the outlet strips has MOVs for surge protection and quite often they fail with a large surge.  Consequently, "from that point on there is NO protection and the owner lives in his own happy world not realizing that he is no longer protected."

Please comment on this. 
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W8JI
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« Reply #10 on: October 27, 2012, 09:48:25 AM »

The typical power strip surge protector has an MOV from hot to gnd and neutral to gnd. If a common mode spike occurs the MOV will conduct to gnd. Now the only gnd connection is normally maybe 100 to 150 feet of #12 or #14 wire back to the panel.

Ground is NOT required to protect a device. If ground actually was required, we would not be safe in a car or in an airplane.

The normal lightning surge path is in common mode, the same direction in all conductors in a bundle. The problem is when two or more bundles of conductors are not common, and run in different directions or to different places. That is what causes most problems.

Quote
That much gnd wire has a fair amount of resistance which causes the voltage at the gnd connection at the surge protector to rise when heavy surge current flows in it. Now if the device connected to the surge protector has any other gnd connections, like an antenna connection, then surge current may flow through the device into these other gnd paths. The result is that, as normally used, these surge protectors are pretty worthless, except for very small surges.

This is why, at TV equipment or telco connected gear, you use something like this:

http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-28-11600-/28-11600

Pick something with at least 1000 joules rating. If you have severe issues, pick a 2000 or higher joule rating. Since I have a 300 foot tower that gets hit at least once in every thunderstorm, I use something heavier. I use these:

http://www.mcmelectronics.com/product/28-8863&green=11118196796&utm_campaign=MyBuys&utm_medium=Recommendation&utm_source=prod&utm_term=28-8863
 
You can see them behind my TV system and in my radio room here:

http://www.w8ji.com/station_ground.htm

Family room here:

http://www.w8ji.com/consumer_equipment_rfi.htm

Quote
Good lightning protection provides a low impedance path BACK TO EARTH GROUND that doesn't flow through any of the protected equipment.


Not really. Lightning protection simply requires the lightning path be OUTSIDE the protected cluster of equipment. The path to earth is important at or near the strike point, but not downstream. I would make things worse if I grounded at my TV sets.

As a matter of fact a house has about the same protection with or without a ground rod at the entrance. What really does nearly all of the work is the bonding of all conductors to a common point. The standard ground rod is really almost a joke as a ground path, but it works quite well as a common connection point. It is required, but we shouldn't delude ourselves into thinking it is a significant earthing path.


Quote
That's the purpose of the "single point ground" at the entrance point. Lightning will always try to find its way back to the Earth. If you don't provide a path then it will find one which may flow through sensitive electronic equipment or, in worst case, through building materials that may ignite. Lightning current, like all electric current, divides among parallel paths in proportion to their or impedance (Ohms law).

The normal lightning surge is in common mode on power mains. All conductors, the neutral and two hots, generally have the vast bulk of current flowing in the same direction.

What the ground rod mostly does is provide a common point for telco and CATV conductors, as well as the mains. The common connection reduces currents that loop through the house and things inside the house from one service to the other.

A typical ground rod has tens to hundreds of Ohms resistance across the bandwidth of a lightning hit, so it isn't much grounding at all. The bulk of any substantial grounding is through all the long wires connected to the utility system.

What we do not want are current looping through the house wiring flowing in on a mains, and out on a telco or CATV line. We do not want them flowing into a well from the mains.

This entire issue is pretty complex, but to protect things in the house we need to not have currents loop through the devices we want to protect. That normally does not require a ground path, and a ground path can often make problems worse.

73 Tom

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N4NYY
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« Reply #11 on: October 27, 2012, 06:16:44 PM »

I got hit by lightning thru the cable TV line. That was connected to my TV, connected to a power strip, which had my laptop plugged into, which had a USB-serial adapter connected to my FT-950. My rig control was blown out.

So, since that time, I went to a single point ground entry box with Alpha Delta surge surrpressors, and bonded my shack rod to my service panel rod.

I also put this on my FT-950's serial port: http://www.amazon.com/APC-protectnet-serial-protector-ps9-dte/dp/tech-data/B007TL34G0

I put these on my TV power, cable line, and Astron power supply: http://www.amazon.com/APC-P8VT3-Outlet-2770J-Protector/dp/B0012YJQWQ/ref=sr_1_1?s=electronics&ie=UTF8&qid=1351386935&sr=1-1&keywords=apc+surge+protector
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W8JI
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« Reply #12 on: October 28, 2012, 05:45:52 PM »

My 300' tower gets whacked every thunderstorm, and this has been going on since 1998. Worse yet, Georgia is second only to Florida for frequency of thunderstorms.

Because of the outlet strips with a pass through for the MATV cable, I've yet to lose any consumer gear from a strike. I've had some of the old CRT TV sets get magnetized from the magnetic field after a storm, but I unplug them and let them degauss and they are fine again.


 
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N4NYY
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« Reply #13 on: October 29, 2012, 06:04:29 AM »

My 300' tower gets whacked every thunderstorm, and this has been going on since 1998. Worse yet, Georgia is second only to Florida for frequency of thunderstorms.

Because of the outlet strips with a pass through for the MATV cable, I've yet to lose any consumer gear from a strike. I've had some of the old CRT TV sets get magnetized from the magnetic field after a storm, but I unplug them and let them degauss and they are fine again.


 


Are you going to set up an auto trigger and get some shots? Maybe submit them to QST.
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AA4PB
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« Reply #14 on: October 29, 2012, 06:41:14 AM »

"Ground is NOT required to protect a device. If ground actually was required, we would not be safe in a car or in an airplane."

True that ground is not required **IF** you locate all of your equipment inside a Faraday shield with no external connections to any of it. Unfortunately, most equipment has numerous external connections and paths to ground. If you don't believe it, try sitting in your car with one foot hanging out on the ground while the car gets hit with lightning.

Normally the goal is to provide a very low impedance path to ground (outside the building) that will carry most of the current to ground and (due to Ohm's law) minimize the current that flows through the other equipment-to-ground paths.

Are you saying that your 300 foot tower has no ground connections? Your "Home Depot" power strip surge protector is the only lightning protection for your equipment?

If the lightning currents are common mode then how does an MOV across the line protect anything. If equal currents are flowing the same direction in both conductors then there is no voltage potential to fire the MOV. The fact is that the current in both conductors is going to attempt to find a path back to Earth ground, possibly through your equipment. The MOVs from hot and neutral to ground will fire and attempt to send the current flow back to the Earth ground at the service panel. The problem is that there is usually a lot of resistance (and inductance) in the grounding conductor from the outlet to the service panel so a good deal of the current takes a parallel path to Earth ground through the equipment.

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