> I'm having new HVAC installed and interested in having a whole-house surge > protector installed at breaker panel to protect equipment from > spikes, sags caused by typical line current and lightning. Too many accurate and other bogus replies to praise or correct. Some will be addressed here. 'Whole house' protection is the only solution for protecting all household appliances - especially electronics. But a protector does not do protection. You earthing must be upgraded to both meet and exceed post 1990 National Electrical code. All electricians understand how to meet code. Only a few understand what is necessary to make the same earthing system sufficient for surge protection. Your earth ground must be upgraded so that the connection from breaker box to earth, via the protector, is short (ie 'less than 10 feet'). For example a bare quarter inch copper wire leaves the breaker box to earth ground. You follow that wire. If it goes up over the foundation and down to an earth ground rod, then it is too long and has too many sharp bends. Protection subverted. That wire must go through the foundation and down to earth ground. Many feet shorter. No sharp wire bends. Ground wire separated from all other electrical wires. Again, concepts that so many electricians do not understand. And also why plug-in protectors do not even claim to provide effective protection. If the only ground wire is to cold water pipes, your earthing is so insufficient as to essentially not exist (for surge protection). To not even meet human safety codes. The most critical component in every surge protection system is not a protector. A protector is nothing more than a connecting device. Your protection is earth ground. Only a few electricians have sufficient electrical knowledge to understand what that means. Why, for example, sharp wire bends going over the foundation subverts surge protection. Or why the ground connection must be single digit feet long - as short as possible. Same applies to any other wire entering the building. For example the cable TV wire must also connect just as short to the same earth ground before entering. Any wire that enters without being first earthed puts your HVAC (and all other household electronics) at risk. How to make better protection? Any money wasted on plug-in protectors is better spend upgrading the earthing. How to make the same âwhole houseâ protector even more effective? Upgrade and expand the earthing. A protector is only as effective as its earth gorund. Which is why adjacent protectors do not claim to do protection. And sometimes can make electronics damage easier. Distance between protector and appliance increases appliance protection. Shorter distance from protector to earth also increases all appliance protection. Just another reason why a 'whole house' protector is so effective for HVAC. A minimally sized protector starts at 50,000 amps. Only those educated by retail myths will define a protector as a one shot device. If any protector fails during a surge, the protector was probably a scam. 50,000 amps because an effective protector connects even direct lightning strikes (ie 20,000 amps) to earth. And remain functional. And does same for all smaller surges. Hard honest answers come with numbers. One that is important. A âwhole houseâ protector starts at 50,000 amps to make even lightning irrelevant. About 50,000 amps or higher. Another critical number - less than 10 foot connection to single point ground. Lightning strikes utility wires down the street. That is a direct lightning strike to all household appliances if the âwhole houseâ solution is not implemented. Not every appliance is destroyed. A surge will choose which to damage by chosing a path to earth. However, if the surge is earthed before entering, then no energy is inside hunting destructively via appliances. The most common surge is a lightning strike to incoming wires. Sometimes (much less often), lightning may seek earth via a chimney or via the attic light. So we also earth a lightning rod. But one should consider the risk. A destructive surge (lightning and other sources) occurs maybe once every seven years. Lightning averted by a lightning rod is even less frequent. One must learn from numbers such as neighborhood history to determine if a lightning rod is also necessary. TV roof antennas properly earthed as required by code also act as lightning rods. A 'whole house' protector will also avert house fires and other problems created by power strip protectors. Protection is always about where energy dissipates. If that energy is inside the house (ie via a cable TV wire), then nothing stops a hunt for earth destructively via appliances (ie computer). Either a surge connects short to earth before entering. Or all appliances (electronic and motorized) are at risk. A âwhole houseâ protector is also necessary to protect power strip protectors that are often so grossly undersized as to be one-shot protectors. All appliances contain massive protection. Anything a plug-in protector might do is already accomplished inside every appliance (including the HVAC). Your concern is a rare and destructive surge that can overwhelm protection already inside appliances - including HVAC. That surge is only averted by earth ground. Either a protector connects destructive energy to earth outside the building. Or that protector is best called a scam. Utilities can rent or install a 'whole house' protector behind the meter. But utilities do not install earth ground. Only the homeowner is responsible for providing and maintaining the only thing that provides surge protection - single point earth ground. Wires underground do not provide surge protection. Every wire (overhead or underground) inside every cable must connect short to single point ground. No exceptions. If not - if a buried wire interconnects two buildings. Then a surge to one building can act like a lightning rod connected to appliances in the second building. Even underground wires that enter each facility must connect short to single point ground. Sags are not averted by protectors. Even incandescent bulbs dimmed to 50% intensity means ideal power to all electronics. But that can cause havoc to motorized appliances (ie HVAC). Therefore an HVAC controller must make sags irrelevant. If voltage drops too low, the controller must stop motors. And if power is restored too quickly, then the controller must wait long enough for a restart to cause no damage. Sags are addressed by properly designed electronic controllers. Surges can only be averted where wires enter the building - via earth ground. A âwhole houseâ protector is required by everyone reading this. Only effective protection for every household electronics including bathroom GFCIs, smoker detectors, dishwasher, computers, and HVAC. One 50,000 amp âwhole houseâ protector connected as short as possible (ie âless than 10 feetâ) to single point earth ground. And an expanded earthing system.

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. ==========

Hope you don't mind but I'd like to ask about my similar situation. Our service comes into our main panel in the barn. From there it goes to the service panel in our house (not attached to the barn). And we have a standby propane generator that is not yet hooked up to the service panel in the house (under construction). Our new home is in an area with frequent lighting strikes (and we have the scorched trees to prove it). We've had the power company out twice in the last 6 months when the transformer tripped. One of the strikes burned out all the exterior lights on the barn and an overload fuse on the well pump in the house. At the time of the strike, the power to house was actually turned off from the main service panel in the barn. Power was just running from the service to the main panel. I think that getting a whole-house surge protector might help to prevent or at least lessen damage. Do we need a whole-house surge protector for each ... barn service panel, house service panel, and generator? Or just one surge protector? I'm sure out electrician will know what to do but I'd like to get an idea of what we will need so I can budget.

Older thread, but I wanted to add my thoughts for others searching the older threads. I also have a 1955 house, so was in a similar situation as the OP. My four 120 V circuits, before improvements: 15 Amp (ungrounded) - All interior/exterior lighting 20 Amp (ungrounded) - Dining/Living/Bed rooms outlets. 20 Amp (grounded) - Kitchen and Bathroom outlets. 20 Amp (grounded) - Detached Garage loads. Earth Grounding - None, or ineffective. Using a section of conduit run. Surge protection - None. Panel - 10 space 100 Amp Zinsco! What I did to improve the system, and make nearly as safe (and in most ways more safe) compared to new construction. This assumes your wiring insulation is still in good condition and not crumbling off the wires! Each of these steps are easy for a DIY type to do themselves (except maybe the last one). 1. Replace all the outlets and switches. Inexpensive, and the old ones will probably be worn out. 1. Add a GFCI outlet to the first outlet on each circuit, and wire to protect all downstream outlets on the same circuit. If the box is too small for the GFCI outlet, they make plastic surface-mount extension boxes that will fit over top and give you the extra room. 3. As the lighting circuit is ungrounded, Make sure to swap over to plastic switch covers, if needed. 4. As the lighting circuit is ungrounded, add a new junction box before the first light in the circuit, and wire in a blank face GFCI outlet there to protect the lighting circuit. Put it at the ceiling, about a foot from the existing first light fixture, then run a couple of feet of new Romex from the new GFCI to the existing first light fixture. 5. Insure you have a good earth ground. Near your main electrical panel, drive (at least) two new copper ground rods at least 6 feet apart, and daisy chain connect to the ground buss of the main panel using 6# copper wire. 6. Install a good whole house surge suppressor at your main panel. You will need the space to add a 220V breaker. I used a Square D HEPD80 in my upgrade. Finally, 7a. Is your main panel obsolete or dangerous? Federal Pacific Electric and Zinsco brand? Replace the panel with a modern one. I had a Zinsco and replaced it myself with a Square-D QO panel, because they are one of the best, oldest, and fastest breakers available. QO was introduced in 1955, and is still one of the most popular today. 7b. If your panel is not obsolete, then swap out all the the 15/20 amp circuit breakers for CAFCI breakers. This will help keep an eye on the condition of your older wiring insulation that's hidden from view. My four 120 V circuits, after upgrades: 15 Amp (ungrounded, plastic switch covers, CAFCI and GFCI protected) - All interior/exterior lighing 20 Amp (ungrounded, but CAFCI and GFCI protected) - Dining/Living/Bed rooms outlets. 20 Amp (grounded and CAFCI and GFCI protected) - Kitchen and Bathroom outlets. 20 Amp (grounded and CAFCI and GFCI protected) - Detached Garage loads. Earth Grounding - New, latest code compliant. Surge Protection - Whole house, 80,000 Amp surge current rating Panel - 42 space 100 Amp Square-D QO Total cost for parts/material for all the upgrades listed above was under $750, and I did the labor myself. I'm happy with the new safely level achieved. A side note: For years now, I have had ZERO problems using AFACI and GFCI on every 120V 15/20 circuit. IMO, if you have a tripping problem, trust the protection device. Find the defective connection, wiring, or item causing the tripping.