Thanks to all for your insights! This does help so much. I am going to consider the whole-house protector, and have actually found a good electrician who I would use for this. His view on it is: it can't hurt and it may help under many circumstances, although as pointed out above, he notes that lightening is a different thing than a "regular" surge that comes through the system. I am definitely already unplugging, unplugging, unplugging whenever I am away from the home office for any time at all (since we have had very sudden storms come up in recent weeks, even a quick run to the supermarket seems risky!). This is also a way to save electricity, since as I understand it, those little boxes that plug into the surge protector that run various pieces of equipment continue to use electricity even when you are away from the device--unless you shut things off and UNPLUG. As for backup computer storage, I am "shopping" right now for an external hard drive with "ghosting" capabilities, which I understand will simply "copy" the entire hard drive so if I have another event, I simply attach my back up external drive to another computer and everything is there (software, all the settings, and so on).

To clarify for anyone not familiar with the problem, what joed is talking about is the need for a transfer switch. A transfer switch assures that your generator power can't get back out to the power company lines. If you didn't know to turn off the main breaker, or forgot, or got the wrong one, or somebody else in the household messed with it, then your generator could energize a piece of the neighborhood wiring and electrocute a lineman who thought it was dead (and maybe had just tested it before you plugged in). We've had posters on this forum tell of people they knew who died that way. I recently heard of a case close to me where someone was supplying his neighbor with power by accident. Fortunately in that case no one was hurt.

bud wrote: "If the energy hits are much smaller, the cumulative energy rating is much higher." brickeyee wrote: Except that each one decrease the maximum energy that can be handled, and lowers the break over voltage slightly. __________ Geez - someone intelligent to talk to. But the MOVs still function and limits the voltage. The cumulative energy rating still increases (as can be seen from characteristic curves for MOVs). (I am assuming in all cases MOVs are used on power wiring. There are different problems if you are using them on, for instance, telephone wiring.) ========== brickeyee wrote: You can end up with a device that will open circuit while high voltage is still present, resulting in downstream damage. __________ They are open circuit after catastrophic failure. Normal failure for MOVs on power circuits is conduction on normal voltage and thermal runaway. The thermal disconnects required by UL since 1998 disconnect the overheating MOVs before catastrophic failure. Msrtzloff says catastrophic failure is more likely caused by overvoltage (discussed below) than a "surge". ========== brickeyee wrote: It takes a vanishingly small amount of actual energy to damage many electronics. Even micro-amps at a high voltage can destroy semiconductors in a single pulse lasting a few nanoseconds. __________ Sure. Risetimes of surges coming in on power, phone, cable service wires are limited by the inductance of the supply wiring. MOVs are fast enough for any such surge. Some other devices, like gas discharge tubes aren't since they require an arc to be initiated. ========== bud wrote: "maximum surge that had any reasonable probability of occurring" brickeyee wrote: If he only considered lightning he failed to account for distribution line problems like falling wires. The fault current in the grid is far in excess of 10,000 amps per wire. Composite interrupt ratings are higher for this reason. __________ As I wrote, crossed power wires are not "surges" and you can not rely on either service panel or plug-in protectors for protection. They are not designed for it. (There are some plug-in protectors that are supposed to disconnect on overvoltage, and a UPS may safely disconnect.) ========== brickeyee wrote: Lightning is rather nasty, with multiple strokes in a single strike, and a huge range of voltages and currents (2 kA to 250 kA, Integral i^2dt from 6E3 to 1.5E7 A^2s, and flashes from 0.15 ms to 1.100 seconds). __________ I have not seen data on surges anywhere near 1.1 seconds. The probability of a surge that is beyond 10kA is very low and the probability of protector failure is correspondingly small. Martzloff has argued that long surge events would result in far higher incidence of protector failures than is seen. ========== bud wrote: "The normal failure mode of a MOV is it starts to conduct at normal voltages (after any surge) and goes into thermal runaway." brickeyee wrote: And then fails open, by accident or design. __________ On power circuits catastrophic failure occurs after thermal runaway at normal voltages. UL required thermal disconnects disconnect failing MOVs before they catastrophically fail open. ========== brickeyee wrote: I have spent over 30 years now designing protection for electronics, including 'operate through' systems (operate during occurs more by luck with smaller strikes). TELCOs have needed better and better protection as they have switched from mechanical stepper relays to electronic switching. A pulse that might barely tickle the old mechanical systems can wreak havoc if it get very far into the electronic central offices now in common use. One of the isolation methods is to take local loops and multiplex them onto a fiber optic link withing the CO. The vulnerable equipment is isolated from the local loops. __________ I agree vulnerability of all the new electronics is a challenge. Fiber optic (and wireless) makes protection of equipment with connection to both power and signal a lot easier. When you move out of a house and into an extended commercial or industrial setting problems with different ground reference voltages become a lot greater. I expect most people here are interested in residential. ========== bud wrote: "Only 5% of lightning strikes are stronger, and the strike was extremely close." brickeyee wrote: The 5% limit for a negative first stroke and flashes is 150 kA, and 250 kA for a single positive flash. __________ Every source I have read is the percentage of all lightning strikes that are over 100kA is about 5%. ========== brickeyee wrote: And it can hit all the way up to the service drop on the side of the house. There is not reliable way to protect from these strikes in a residential setting. __________ But the probability is extremely low. That is the point of the 10kA figure (which is also in the IEEE surge guide) - there is a very low probability of a worse event. The figure I saw was once in 8000 years. It is not practical to design anything for the worst possible case. ========== brickeyee wrote: Service equipment is often destroyed. The service drop from the weather head serves as a crude guide to a final earth flash, with damage to the panel and interior wiring of the house not all that uncommon. Buried lines are significantly better (not very likely to be struck directly, and the line insulation often fails at extreme overvoltage if distribution lines are struck and it gets past the transformer). ========== bud wrote: "My understanding is that there is not likely to be significant damage." brickeyee wrote: The arcing over in the panel creates damage in and of itself depending on the exact path it takes. __________ The arc voltage is, if I remember right under 500V, but call it 500. Assume 10kA surge current for 100 microseconds. The energy is 500 joules. That is the energy from a 120V 4A load for 1 second. Panel damage does not seem as likely as it would seem. ========== brickeyee wrote: The flash can damage insulation on wires in the panel, damage circuit breakers (especially GFCI and AFCI devices with electronics), and even cause fires in panels. It is not a pretty sight to open and examine a panel that has received a nearby stike. __________ But again probability of major damage is low. A service panel protector with a high surge current may have a let through voltage high enough to damage AFCI/GFCI breakers. I have no idea what their withstand voltage rating is. ========== bud wrote: "And a direct strike to the building requires lightning rods for protection - but you are not talking about a direct strike." brickeyee wrote: And there are far more houses without rods than with, meaning the building itself and its utility wiring is an easy entry point. I remember watching a 3 story townhouse that was struck with extensive fires ignited throughout the attic and top two stories. We watched the whole thing from strike to the FD getting it under control from out nearby 6 story office building (we had already had antennas, transmitters, receivers, lab equipment, and even some upper floor building wiring damaged from a failure to bond the rebar in the building adequately during construction). Within the 3-4 minutes for the FD to respond (semi-rural area) the attic and third floor had become fully involved, with flames starting to exit some second story windows. The firewall to the adjacent unit held up adequately, but the entire unit was declared a loss and then demolished down to the basement slab and then rebuilt __________ As I said, to protect from a direct lightning strike you need lightning rods (now called air terminals), which is not what the discussion has been about. ========== bud wrote: "Then the inductance of the branch circuit greatly limits the current, and thus energy, that can reach the protector." brickeyee wrote: But the inductance also serves to increase the voltage created. Free lunches remain unavailable. __________ There is inadequate information on what you have in mind. The inductance of the branch circuit limits the current. It will somewhat lengthen the duration of the surge. But the fact remains that with a 10,000A surge on the incoming power wire the maximum energy absorption at a plug-in protector was 35 joules. The maximum was not even for the largest surges. The largest surges forced the voltage at the service above 6kV and arc-over. For some smaller surges (with the shortest branch circuits) the MOVat the protector held the voltage at the panel below 6kV and there was no arc-over. One of them resulted in the maximum energy of 35 joules. The voltage at the panel was higher than the stable arc-over voltage but lower than 6kV. ==========

I'm glad to be of help. I take your point re allowing Comcast to replace the modem ;) if it's cooked, however, if you're in business you may not want to wait a week til they can come out if it's busy following a severe storm....one argument in favour of buying your own I suppose - downside of unplugging the modem for an extended period? It may lose its provisioning, which will mean you'll probably get a 'welcome to comcast' screen which you can't get around til you contact them...not usually a big issue and if you set your DNS servers to use Open DNS not so much of a problem although your speed is usually 'shaped' or limited too. Your laptop, having a battery, is a form of ups in itself minus the robust surge protection, but a decent surge protector will help. If you have an external back up drive, always a good idea, get a bus-powered one which connects just with an usb or firewire cable and requires no other power cable, this will run from the laptop's battery til you can shut down...but I still think a ups is a cheap investment for any essential powered accessories like modems routers, back up drives etc. Mine paid for itself in thirty seconds when the power dropped briefly while editing a video (my former business) no damaged hardware, my render wasn't interrupted, and no corrupted data. Just today I had to run a winsock reset for a customer who was affected by a severe storm and a power outage, no electrical damage but the computer experienced some corruption nevertheless. How much is your data worth? Getting a business class internet account may be wise, your comcast terms probably say you are *not* allowed to run/do any sort of business on a residential account, on the upside the business svc should offer better/more helpful products. Glad to hear you unplug the data side too, however, leaving the phone line in has a risk, if it connects to your all in one fax printer, it still has a path to your computer. A smart individual would build an isolating cutoff box capable of disconnecting power, data/coax/phone altogether with a high degree of isolation (you watch, they'll be on the market next week)