Im posting on this to bring this thread back to life. Lots of good information here. I just saw this post from Uniondawg and feel kind of relieved. Artisian is one of the pool builders I wanted to get a quote from. He didnt seem to want the business. We live out of state, and are building in the Charlotte area. I told him we were coming in for a few days for the sole purpose of meeting with a few pool builders and he couldnt find an hour to give me, even a month out. I felt like I was begging him to take my business. After asking about three different times on two different days and being met with, "thats family time, or Im pretty sure im booked" it was obvious to me he wasnt interested in my business. He was very nice, but strange behavior for a business man. Too many other pool builders in the area to be dealing with that. Plenty of other reputable pool builders out there that want the business.

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. ==========

> Even ham antennas rarely survive unscathed from a strike. Myths are widespread and easily promoted. Meanwhile, Alan Taylor of the US Forestry Service documented that well over 95% of trees struck by lightning even have no appreciable indication. Direct lightning strikes without damage is routine. Damage is even less likely when items (ie ham antennas) are properly earthed. Only hearsay and emotion deny that reality. Hyperbolic claims have been made by ignoring facts and experience. A professional discusses reality: > Well I assert, from personal and broadcast experience spanning 30 years, > that you can design a system that will handle *direct lightning strikes* > on a routine basis. It takes some planning and careful layout, but it's > not hard, nor is it overly expensive. At WXIA-TV, my other job, we take > direct lightning strikes nearly every time there's a thunderstorm. Our > downtime from such strikes is almost non-existant. The last time we went > down from a strike, it was due to a strike on the power company's lines > knocking *them* out, ... > The keys to effective lightning protection are surprisingly > simple, and surprisingly less than obvious. Of course you *must* have a > single point ground system that eliminates all ground loops. And you > must present a low *impedance* path for the energy to go. Another professional who says what makes the OP's 'whole house' protector so effective. Unsupported and subjective accusations of unavoidable damage and useless earthing does nothing to answer OP's question about adding a safety ground. Assumed destructive transients created inside a building comes from another subjective claim not supported by facts. His 'whole house' protector and superior protection already inside every appliance also makes that noise less problematic. Damage from direct lightning strikes is so routinely and easily averted that damage is considered a human failure. Often found where one assumes a 'woe is me' attitude. OP has earthed a best solution available to every homeowner. Advantages of a safety ground are an unrelated topic.

Metal piping do act as grounds. Lightening may strike the highest part of the plumbing and it will go through the roof to do it. This type of grounding offers no protection. It is like a lightening rod inside the house. The best protection is a tree or tower near the house that is taller than the house. A metal flag pole acts as a lightening rod. Generally speaking, objects within a 30 deg cone drawn from the top of the pole are somewhat protected. However, there is no guarantee that it will not be hit for all strikes. The voltage potential just before the strike is extremely powerful. The path from ground to cloud gets ionized and then the charge suddently dumps along the path of least resistance. Flag poles and trees are hit on a regular basis so its not a good idea to be near the base of these things because you may become part of the discharge path.