Surge Protectors
in [Repair]
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From: vjp2.at on 28 May 2010 23:50 Well, here's is a disclosure of the biases which might be distorting my thinking: In February and August 2001 I lost two external modems to lightning (caused my line to be off-hook until disconnected modems) and someone on usenet told me to tie a ground to the modem. That particular computer (Ampro 2210 80186 hooked up to 1980 HP2621a terminal) with modems had previously survived 1988-1995 without problems (no phone surge supressor but one on power). In 2008 I lost two LCD monitors the same week during light rain. I am therefore excessively (and probably unreasonably) cautious of using computers during bad weather. Also in 1980 I took two semesters of EE for non-EEs (am a 1981 ChE). - = - Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus, BioStrategist http://www.panix.com/~vjp2/vasos.htm ---{Nothing herein constitutes advice. Everything fully disclaimed.}--- [Homeland Security means private firearms not lazy obstructive guards] [Urb sprawl confounds terror] [Phooey on GUI: Windows for subprime Bimbos]
From: vjp2.at on 28 May 2010 23:57 *+-even the cheap suppressors I've bought had 3 MOVs,one for each leg to *+-ground and from one leg to the other. I guess that's a "delta" config. Do surge supressors exist for two-line phone connections? WOuld it make sence to put a surge suppressor (what kind?) on my incoming phone line? Neighbors have complained of fried modems, but curiously I don't remember anyone ever telling mtheir computer got fried. - = - Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus, BioStrategist http://www.panix.com/~vjp2/vasos.htm ---{Nothing herein constitutes advice. Everything fully disclaimed.}--- [Homeland Security means private firearms not lazy obstructive guards] [Urb sprawl confounds terror] [Phooey on GUI: Windows for subprime Bimbos]
From: Michael A. Terrell on 29 May 2010 00:22 vjp2.at(a)at.BioStrategist.dot.dot.com wrote: > > *+-even the cheap suppressors I've bought had 3 MOVs,one for each leg to > *+-ground and from one leg to the other. I guess that's a "delta" config. > > Do surge supressors exist for two-line phone connections? > > WOuld it make sence to put a surge suppressor (what kind?) on my > incoming phone line? Neighbors have complained of fried modems, but > curiously I don't remember anyone ever telling mtheir computer got fried. There should already be one inside the phone company's Network Interface. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
From: Cydrome Leader on 29 May 2010 20:34 Michael A. Terrell <mike.terrell(a)earthlink.net> wrote: > > vjp2.at(a)at.BioStrategist.dot.dot.com wrote: >> >> *+-even the cheap suppressors I've bought had 3 MOVs,one for each leg to >> *+-ground and from one leg to the other. I guess that's a "delta" config. >> >> Do surge supressors exist for two-line phone connections? >> >> WOuld it make sence to put a surge suppressor (what kind?) on my >> incoming phone line? Neighbors have complained of fried modems, but >> curiously I don't remember anyone ever telling mtheir computer got fried. > > > There should already be one inside the phone company's Network > Interface. This applies to the US- there are surge and lightning arrestors on phone lines where they enter a residence, and they're grounded to something good, like a water pipe for instance. It works great. Now if lightning surges hit your power then what happens? a cheapo-garbage "surge protector" like a power strip or the like will use MOVs to short out line to neutral or even line to ground. What happens if you throw a short across line to ground and can somehow clamp it to 600 volts or whatever? The numbers are made up, but concept is the same. well, your ground ends up at 300 volts above actual earth ground where that device is located. This assumes your ground has the same impedance as the current carrying conductors. So now your computer isn't really grounded, and floating at a potential way off what the phone like is at, which worst case is being protected to a really solid ground, and not hundreds of feet or wiring in your walls or whatever. This is what blows up stuff like modems or devices that sit between your outlets and a phone line. The best move is to install a service entrance surge supressor. They'll clamp surges at the best ground you've got, with the lowest possible impedance, and at your ground/nuetral bonding point not at your load where any attempts to do so are pretty useless across the extra fraction of an ohm. You can easily test the resistance of your wiring at home too, and at the same time actually test if your ground is solid. connect some large resistive loads like halogen lamps, hairdryer, toaster oven or whatever at and outlet. Measure the voltage drop when it's on. Break out the suicide cables and test that same device using line to ground. Depending on how your place is wired, you may find that under an actual load, your ground is really awful. A volt meter won't pick crappy ground connections unless you are actually running real current through it, so just reading 120 across hot and ground and saying "looks good" really doesn't count. Trying to suppress a surge with a $4 power strip connected though 5 junction boxes connected with BX cable can really just be a big joke.
From: bud-- on 3 Jun 2010 14:01
Cydrome Leader wrote: > Michael A. Terrell <mike.terrell(a)earthlink.net> wrote: >> vjp2.at(a)at.BioStrategist.dot.dot.com wrote: >>> *+-even the cheap suppressors I've bought had 3 MOVs,one for each leg to >>> *+-ground and from one leg to the other. I guess that's a "delta" config. >>> >>> Do surge supressors exist for two-line phone connections? >>> >>> WOuld it make sence to put a surge suppressor (what kind?) on my >>> incoming phone line? Neighbors have complained of fried modems, but >>> curiously I don't remember anyone ever telling mtheir computer got fried. >> >> There should already be one inside the phone company's Network >> Interface. > > This applies to the US- > > there are surge and lightning arrestors on phone lines where they enter a residence, and they're > grounded to something good, like a water pipe for instance. > > It works great. Some comments are somewhat specific to the US. A couple of excellent sources of info on surge protection are: <http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf> from the IEEE, and a much simpler one from the US-NIST <http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf> With a strong surge current to the earthing electrode, the "ground" for the building can rise thousands of volts above "absolute" earth potential. You want power and phone (and cable) wires rise together. That requires a short ground wire from the telephone entrance protector to the earthing system at the power service. > > Now if lightning surges hit your power then what happens? > > a cheapo-garbage "surge protector" like a power strip or the like will use MOVs to short out line > to neutral or even line to ground. > > What happens if you throw a short across line to ground and can somehow clamp it to 600 volts or > whatever? The numbers are made up, but concept is the same. > > well, your ground ends up at 300 volts above actual earth ground where that device is located. This > assumes your ground has the same impedance as the current carrying conductors. > > So now your computer isn't really grounded, and floating at a potential way off what the phone like > is at, which worst case is being protected to a really solid ground, and not hundreds of feet or > wiring in your walls or whatever. > > This is what blows up stuff like modems or devices that sit between your outlets and a phone line. If you RTFM, any competent plug-in suppressor manufacturer should tell you the phone wires have to go through the suppressor along with the power wires. The voltage on all wires is clamped to the ground at the suppressor. The voltage between the wires to the protected equipment is safe for the protected equipment. All interconnected equipment needs to be connected to the same suppressor, or external wires, like cable need to go through the suppressor. This is clearly explained in the IEEE guide starting pdf page 40, and shown in the examples at the end. Plug-in suppressors work primarily by clamping, not earthing. > > The best move is to install a service entrance surge supressor. They'll clamp surges at the best > ground you've got, with the lowest possible impedance, and at your ground/nuetral bonding point not > at your load where any attempts to do so are pretty useless across the extra fraction of an ohm. Service panel suppressors are a real good idea. I would particularly use one in high risk areas like Florida. But from the NIST guide: "Q - Will a surge protector installed at the service entrance be sufficient for the whole house? A - There are two answers to than question: Yes for one-link appliances [electronic equipment], No for two-link appliances [equipment connected to power AND phone or cable or....]. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be NO - but that does not mean that a surge protector installed at the service entrance is useless." The NIST guide suggests most damage results from high voltage between power and phone/cable wires. A service entrance suppressor does not, by itself, limit that voltage. > > You can easily test the resistance of your wiring at home too, and at the same time actually test > if your ground is solid. > > connect some large resistive loads like halogen lamps, hairdryer, toaster oven or whatever at and > outlet. Measure the voltage drop when it's on. Break out the suicide cables and test that same > device using line to ground. > > Depending on how your place is wired, you may find that under an actual load, your ground is really > awful. A volt meter won't pick crappy ground connections unless you are actually running real > current through it, so just reading 120 across hot and ground and saying "looks good" really > doesn't count. May well be worthwhile. But even with a good earth connection the building ground can rise thousands of volts. > > Trying to suppress a surge with a $4 power strip connected though 5 junction boxes connected with > BX cable can really just be a big joke. Neither the IEEE or NIST agree. Both guides say plug-in suppressors, used correctly, are effective. Plug-in suppressors with very high ratings are readily and cheaply available. In the US you should only buy suppressors listed under UL1449. UL tests include a testing to at least a minimum floor of protection. UPSs with surge protection should also have UL1449 listing. ========== If there is a strong surge on power wires, with no power service suppressor, at about 6kV there is arc-over from the hot busbars to the service panel enclosure. After the arc is established, the arc voltage is hundreds of volts. Since the enclosure is connected to ground-neutral-earthing electrode, most of the surge energy is dumped to earth. A surge is a short event, thus a relatively high frequency event. The impedance of the branch circuit greatly limits the current to a plug-in suppressor (unless the branch circuit is very short) and thus limits the energy that can reach a plug-in suppressor. For both these reasons the energy dissipated in a plug-in suppressor is surprisingly small. Neither service entrance or plug-in suppressors work by absorbing the surge energy. But in the process of protecting, some energy is absorbed. -- bud-- |