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Let's say there is a lightning strike on a nearby power line and the excessive voltage/current makes it to your house. I often read that grounding rods are there to protect against surges like lightning. But if it is coming in through your wires, unless you have a surge protector redirecting it directly to ground (and thus the rods), wouldn't it first go through the hot wires and the entire circuit/appliances/electronics before returning to the panel and then to the ground rods? Maybe someone can explain the path in this example, lightning going through and into the ground rods with and without a whole home surge protector in place.

Fred
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    The idea is it goes though neutral from the power line, which is bonded/connected to the ground rods. The home surge protector is to help prevent that surge from getting to your electronics, but if the lighting is that close, you might have damage anyway. It is a prevention to help reduce the damage, not a guarantee. – crip659 Jul 29 '23 at 00:05
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    ok I guess I have a hard time comprehending because I picture neutral as the return wire from my panel back to the power company. And in my head I'm looking for that connection in the panel that takes the incoming electricity from the hot wires directly to the neutral and into the ground rods in my yard (bypassing all the circuits). You mentioned going through neutral from the power lines so I'm probably just not understanding something basic but thank you for responding. – Fred Jul 29 '23 at 00:26
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    I believe that when a current has multiple possible paths it can take, it takes them all partially, each in inverse proportion to its resistance/impedance. Thus the idea is to provide very "attractive"=low-impedance path(s) to the earth that do not travel through your stuff. – Armand Jul 29 '23 at 08:15
  • The neutral is connected to the hot wires at the supplying transformer, and also to the grounding electrodes (e.g. rods) at the supplied residences and possibly at the transformer itself. It is all one big web of low-resistance metal. Ideally. – kreemoweet Jul 29 '23 at 10:27
  • I think I get it now. You're saying a lightning strike that successfully got dissipated through the home's ground rods before causing any damage did not necessarily enter through the home's circuit panel, it got routed there via a connection prior to that. – Fred Jul 29 '23 at 11:03

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The neutral or ground is the top wire on the pole.

The lightning also has a very low impedance path from a hot wire to neutral - the utility's transformer. For how transformers deliver power to houses, see this. Now, everybody thinks of a transformer as a thing that supplies power, not passes power. But it's both at once. Transformers have an internal resistance - an impedance - due to their manufacture. Indeed, when modeling power supplies (of any kind) in electronics design software, you must model them as a voltage source and a resistance in series. For instance the secondary of a transformer is one single piece of wire connecting both terminals. It's wound in a coil, and that has effects, but its static resistance is the same as if the wire were stretched out straight. And it's thick wire, so resistance is very, very low. Less than 120/10000 or 0.012 ohms. Remember, any wire resistance in the transformer turns into heat inside the transformer. And by and large they convection-cool.

So yes, lightning can path through that "coiled up wire" very easily to leap from hot to neutral to get to ground.

Still could be bad for appliances attached to the hot wire, but the appliance doesn't take the brunt of the hit. The transformer does.

Harper - Reinstate Monica
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  • This might be the correct answer, but I think many people are not going to understand it; as it relies on implied secondary knowledge. – Ray Butterworth Jul 29 '23 at 01:04
  • I'll be honest, it went over my head. An illustration of the lightning path from transformer to residential home and into the home's ground rods would be optimal. – Fred Jul 29 '23 at 01:20
  • The resistance of the secondary winding - 0.012 ohms in your answer, will be overshadowed by the impedance of that secondary winding to a lightning strike with a rise time of around 10 us. – SteveSh Jul 29 '23 at 20:42
  • @SteveSh that AC impedance will only exist if the transformer's inter-winding insulation holds. – Harper - Reinstate Monica Jul 29 '23 at 21:11
  • A few years ago a very expensive and high featured house was constructed in my neighborhood of 1970 tract houses. The still useable tract house was bulldozed foundation and all. I walked through the new house while it was under construction and . . . amazing. One of the features was ground rods and a UFER grounding! Why both? – Jim Stewart Jul 30 '23 at 09:40