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Old 27th August 2010, 06:52 PM   #11
TechGuy is offline TechGuy  United States
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Originally Posted by indianajo View Post
However MOS suppressors, salvaged from PC power supplies, are free. If TechGuy's ground is 6 ohms, he needs to work on it. My safety pin to neutral is reading 0 ohms on a craftsman DMM, and the meter will detect 2 ohm resistors, so I know it is below that.
I recall reading that the typical resistance of earth ground is 6 Ohms. If your ground to neutral resistance is zero ohms, then I suspect that you have a wiring fault and than someone connected ground to neutral inside your home\business. Try sticking a probe into ground and measuring the resistance. Consider that even copper should have a higher resistance from the transformer pole to inside your home unless they pole transformer is very close. Since earth ground isn't made of copper its going to have a higher resistance. Remember that the Pole transformer Neutral line is connected to ground at the pole. If you look at the pole that has your transformer mounted there should be a ground cable going from the neutral terminal into the ground (unless its not connected correctly). The ground connection from the pole serves as the current loop.

For good quality ground connections carbon backfill is applied into the ground where the ground rod is placed. But this is rarely done.

MOV's degrade every use, and they can return false readings prior to compelete failure. If you want a guarentee that they will work, you basically need to replace them after every storm. A MOV tester can't tell how badly its been degraded unless it performs a destructive testing. MOVs are also very limited in power they can absorb. For Lightning suppresion you want a gas discharge tube to that can handle thousands of amps. The only issue is that GDT have much slower reaction time (measured in milliseconds). MOVs react in nanoseconds. Quality surge suppressors will use SADs (Sillicion Avalanche Diodes) instead of MOVs since the don't degrade, but they are prone to complete failure if they absorb too much energy.

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My teacher at the community college said so, and I lost a modem and the connecting PCI buss slot of the main board of the PC due to a hit.
More often this is because the surge is diverted to ground in low costs surge protectors. The surge travels from phone connection using your own ground cabling. Electricity always follows the path of least resistance. Your modem served as a expensive surge protector sacrificing itself in the process. I think your teacher needs to understand power surges better. He or She is likely making a poor prognosis from direct observation, rather then understanding the problem of surges.

Frequently asked questions about surge protectors / suppressors for the home
"This surge voltage on the ground wire varies along the length of the wire. When equipment such as modems, printers and other computers is interconnected, the interconnecting cable creates a "ground loop".

http://files.meetup.com/247150/Want%...%20Devices.doc
". Most computer modem damage is caused when high energy power-line surges are diverted to the reference ground and coupled into the digital side of the modem. This elevated voltage then seeks the phone line ground reference on the analog side of the modem and arcs through the modem. "

This is why you want a zero diversion surge protection. Cheap surge protectors don't really work, they just push the problem somewhere else. You also want three way surge protection to address common mode surges (ie where both Line and Neutral voltages are raised at the same time). About a year ago, a pole came down in my neighbor it caused a common mode surge that bypass my surge protector because it didn't support common mode surges. I wrote the engineer about the issue, and he did inform that it didn't protect against common mode surges. I searched but I could not find a qualiy surge protector offering three way protection without diverting to ground.
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Old 27th August 2010, 10:26 PM   #12
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You are a US resident. If you have ever changed a breaker in your distribution panel, you will notice the green (safety) and white (neutral) connections are made to the same screw bar. Also connected to that bar is an earth ground, either a pole into the soil, or in this jurisdiction, a connection to the gas pipe or water pipe. Since lightning, by observation, connects the sky to the ground, and the earth ground of the electrical system is connected to the earth where the water table is high enough, I can't see dumping the surge into the earth ground is bad, if the sky is the source. If a neutral disconnect as you postulate is the fault, then dumping the surge to earth is not ideal. However, in this location, the sky erupts surges much more often than poles are torn down. And no screw guns are operated in this residence into the wiring or not- I don't own one, and don't employ slezoid contractors except where required by the electrical company. The last time I did employ electricians, they did screw me - the individual is an easy mark, no matter how knowledgeable.
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Old 28th August 2010, 12:46 AM   #13
ChrisA is offline ChrisA  United States
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Originally Posted by Conrad Hoffman View Post
The first step in beginning any design is to be very specific about what you're trying to accomplish. In this case, who is the enemy you're trying to vanquish? RF noise? Voltage variations? Common mode junk? The guy with the spot welder down the road? Distorted waveforms? Bad building ground? Overvoltage? Undervoltage? Lightening? DC on the mains?...
Seems that you asked to hard of a question and the OP went AWOL. Most people when asked really can't come up with any reason at all. Likey because there is none.

The next question I'd ask a person who wants a power conditioner is "If you do buy one, how will know know if it works?"

My opinion of this is that the best power conditioner should be inside amp's power supply. I just build an amp and I can quickly flick the power switch, disconnecting mains and you have to listen carfully to hear it on the speakers, the filter has a several seconds time constant.
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Old 28th August 2010, 01:45 AM   #14
star882 is offline star882  United States
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What about have common mode surge protection divert to something that is not the normal power ground, such as a metal pipe?

Another solution is to tie every device to a ground bus and protect the external connections just as well as the power. I did just that using a PC case as the bus and one time after a storm, the ADSL connection became unreliable (it was protected by an APC surge protector). Initially, I thought it was the modem or the surge protector, but after noticing that a known good phone was also unreliable on the same line, I called the ISP. Turns out a marginal connection underground blew open and a carbon track was all that allowed it to work at all.
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Old 29th August 2010, 05:25 AM   #15
TechGuy is offline TechGuy  United States
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What about have common mode surge protection divert to something that is not the normal power ground, such as a metal pipe?
I assume that you're suggessting running a seperate line to a separate ground. The question is what if the voltage spike is thousands of volts and the ground connection is 6 Ohms or higher. The grounding connection may not handle all of the energy resulting in some of the surge getting through to cause damage. Plus running a separate ground for all your surge protectors may be costly and difficult.

So far the only way I can think of to ensure full protection is a full simulatious crowbar circuit that virtually isolates the protected device. This would be equivalent to using a meat clever across all three connections (Line, Neutral and Ground).

I am increasing concerned about Solar caused EMP events such as this:
Solar ERUPTION: Powerful Sun Activity Captured By NASA Spacecraft (VIDEO)

Fortunately the CME was headed away from earth. Back in 1997 Canada took a nasty hit from a solar flare that disrupted power. CMEs can cause nasty power surges.
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Old 30th August 2010, 04:20 PM   #16
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In theory (because no-one would be foolish enough build such an energy inefficient and unreliable device) a motor physically coupled to a dynamo (coupling non-conductive) arranged in such a way as to produce 1:1 voltage would provide the kind of isolation guaranteed to survive even a direct building lightening strike, which not even spark gap arrestors will deal with.

I feel safe in providing this useless idea as the original author of the thread has long since fled. As will I.
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Old 30th August 2010, 05:44 PM   #17
tvi is offline tvi  Australia
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zero surge Total Surge Cancellation

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Old 30th August 2010, 05:58 PM   #18
ChrisA is offline ChrisA  United States
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Originally Posted by random007 View Post
In theory (because no-one would be foolish enough build such an energy inefficient and unreliable device) a motor physically coupled to a dynamo (coupling non-conductive) arranged in such a way as to produce 1:1 voltage would provide the kind of isolation guaranteed to survive even a direct building lightening strike, which not even spark gap arrestors will deal with.

I feel safe in providing this useless idea as the original author of the thread has long since fled. As will I.
I've seen these in use. They are called "motor generators" and are more common than you think where very high amounts of clean power are required. They will have a large cast iron flywheel on the shaft and can ride through short transients The last one I saw was powering a large IBM mainframe computer. I think they are used in hospitals too. These are usually large, many, many kilowatts.
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Old 30th August 2010, 06:25 PM   #19
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The zero surge idea is quite interesting, imo... seems that I read about them some time back...

BUT if you read carefully, you will find that they say that their method is not better than a large isolation transformer!

The other thing that I have come to understand is that lightning is NOT only a sky-to-ground thing at all. It is also an earth to sky thing!

There is a real issue imo with Vdrop across ground wires. This makes it difficult to keep everything at the same ground potential.

There is always a major difference in potential between the phone co lines (for example) and the power company lines/ground

In radio transmitter sites, the goal is to distribute the energy of a lightning strike into the ground - not just to a single point called ground. Bonding everything with low Z ground buss is then required.

Oh yes, the safety ground/green wire in the USA does NOT carry current under normal operation, it is there as a safety in case there is voltage present on a chassis (for example) or a GFI needs a reference. The reading between neutral and safety ground should be non-zero on a meter that has decent resolution below 1 ohm, a typical DVM might not have the required resolution.

Grounding to a gas pipe is likely a violation of code.
Remove it asap - that is dangerous.

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Old 30th August 2010, 07:32 PM   #20
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If line signal quality is really what worries you then you probably shouldn't even plug your TV into the same conditioner that your audio equipment is on.

If very reliable spike/surge clamping is really what you're after then you might want to try using an old fashioned, reliable fuse ahead of an appropriate array or single large MOV. Just select the MOV so that it can easily drive enough energy into the fuse filamment to blow it before damaging the MOV. You should find it pretty easy to blow a hundred fuses or many more before wearing out the MOV. It's possible to flash smaller filaments with less energy, so fusing individual loads is better, You can use a series of 250VAC fuses if you are worried about sustained very high voltage arcs. They're not really designed to open very high voltages of course, but the reality after an arc is struck is all about energy lost before the arc extinguishes, and even a 1" tube filled with metal oxide and vapor is going to do better than a cheapo 15A circuit breaker with the contacts right next to each other. What those surge bars do to MOVs is not really the fault of MOVs. If you put enough of them in there, which would be way more expensive than your typical surge bar, you could blow one of those little breakers to pieces before the MOVs flinch.

Fuse both sides of the line (I've seen lots of dead lighting struck equipment and it may be 50/50 that common mode took it out) and if you series holders keep them all in a row and leave plenty of space and lots of good insulation around them. Best to skip small metal boxes. You can hog a couple of the receptacles out of a plastic surge bar.


If what you're really after is a squeaky clean 60Hz sine wave, the price and complexity goes up drastically.

Last edited by Andrew Eckhardt; 30th August 2010 at 07:39 PM.
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