Charging and Thunderstorms

That would be personal preference; it is UL listed as a Type 1 SPD, so it can go upstream of breakers. It's internally fused on each leg for both overcurrent and overtemperature. It is its own NEMA 4X rated enclosure, so it could stick right out of a knockout on your service equipment outdoors, if that turned out to be the convenient, shortest/straightest-wired place for it.

A friend has had one sticking out of the meter/switch box for over ten years, and the green LED did eventually go out, so we know the house got protected from something.

 

You also want your feet close together. When a high current is flowing through the ground, the voltage between your left and right foot is directly proportional to how far apart they are. (Just Ohm's law, only in a case where Ohm has gotten drunk and really mean.)

Make yourself less tall by crouching/squatting on your two feet together, but not on all fours and not by making yourself long on the ground.

The same considerations ("step potential") apply if, for example, you are near a downed high-voltage transmission line. Leave the area with your feet together, hopping, not by walking.

 

Cars are interesting insofar as their metal frame and exterior separated from the ground by four thick rubber tires makes them behave like a classic "Faraday cage" shield. My grandmother was terrified of lightning storms and used to insist on going out for a drive (or just sitting in the car) whenever a storm approached. She had read about this even if she did not understand the science.

She also knew that it was dangerous to get in or out of a car in a lightning storm because you'd have your feet on the ground while touching a very large metal object.

All that being said, an electric car plugged into an EVSE is different because the charging cable is designed to bring voltage inside of the Faraday cage. And, therefore, the car becomes just another piece of electrical apparatus connected to the power grid. (EVSEs provide ground fault protection but not surge protection -- and even if they did, such surge protection would not be effective against any very large voltage surge caused by a nearby direct lightning strike on the power distribution system serving your house.)

Whether it's your large screen TV, audio system, home computer, ham rig, or Prius Prime, it's always best to isolate it from the power grid during any extreme electrical event. (I have seen the motors in sealed commercial air conditioning compressors destroyed by lightning-induced surges.)

Of course, it's not always possible to unplug everything during every electrical storm. But, if you can, it greatly reduces risk of equipment damage.



And, if you live in a lightning-prone area or have a house which is the highest point in the general area, investing in quality lightning protection is well worth the cost.

 

I've forgetfully left my Prime plugged in during thunderstorms with no ill effect. However, my area isn't prone to lightning very often and I live in a mixed urban area with much taller buildings/trees nearby.

Old Bears' explanation is a good one why having a Prime plugged in during a storm can turn out very bad for the Prime. I need to be more diligent of unplugging during storms from now on.

 

Thanks for this link. I've been looking for a type 1 SPD with no luck. Of course there is still the risk that anyone who looks at the panel in the future won't understand that a type 1 doesn't need its own breaker. And I wonder if there is anywhere to connect it to in a full panel? I don't think there are any extra lugs on the bus bars.

Also, I suspect ground electrodes are extremely lacking at my house, but I'm not sure how to check.

 

Getting down to earth....

 

It turns out a digital multimeter isn't really appropriate for measuring ground resistance in a home electrical system. I tried and got meaningless readings. Maybe I can rig up a way to test it by applying a voltage between the ground bus bar and the one exposed ground rod (that I suspect isn't connected to anything)

 

No, an ordinary multimeter won't do the trick at all. For one thing, if your electrical service is connected, there are already various leakage currents flowing in the grounding electrode system and you don't really know how big they are.

If the service isn't connected yet (as in new construction), a three-terminal tester like the ones described in that PDF will work. You need one lead connected to the electrode under test, two other (long!) leads to two temporary electrodes you stick in the ground in specific geometric patterns ... several different ways, to get several readings, which you then boil down with some math.

The instrument has to be clever because as soon as you've stuck some electrodes in the ground, they will pick up all the leakage currents flowing in all directions between your neighbors and your grounded power poles. Those are all (in the US) AC at 60 cycles, so the ground tester does a clever thing. It switches its current source on and off quickly, at a frequency that's higher than 60 and not an exact multiple (say, 130 maybe, but not 120). It measures the detected voltage with a detector that is gated on and off in exact synchronization with the source, and in that way it manages to get a reading that isn't biased by everybody else's stray 60 Hz currents.

If your service is already connected, a 3-terminal instrument isn't enough, because you've got unknown stray currents of your own going right through the electrode you're wanting to test. There are instruments made that have an additional current-sensing clamp you can put around your electrode wire, to detect those currents and compensate for them in the meter's reading.

There's a newer instrument (that PDF was from 1981) for a quick check reading when the service is already connected, that has no electrodes to drive at all. It depends more or less on a theorem that, with your house on the grid, your electrode is parallel-wired with everybody else's electrode and every pole electrode, near and far in your neighborhood, and their combined impedance becomes negligible compared to that of the one electrode you're testing.

Those instruments just have two coils that you clamp around your electrode wire (sometimes physically combined to just look like one fat one); one is a driver coil that inductively makes current flow in your ground circuit, and the other is a current coil to measure how much flows ... again, all done at a frequency chosen to be different from the power line frequency, so it can tune that out.

 

I think an easier solution would just be to add a couple new ground rods.

 

That would be consistent with the principle of the lightning rod as described by Benjamin Franklin in 1749. Franklin developed his discoveries of the behavior of lighting and published his idea for a practical application in 1753. Later, around 1760, he made improvements to his invention, turning the lightning rod into a reliable system.



Some religious leaders of the time thought Franklin's invention was blasphemous because it circumvented God's power as manifest through lightning bolts.

Alas, they may have been correct because if your Prime is destroyed by a lightning strike, your insurer is most likely to pay for your loss in accord with the "Act of God" provision of your policy.

 

Be careful to read that "getting down to earth" PDF where it touches on ground rods too near to each other. They don't end up contributing to better earthing unless they are a certain minimum distance apart (as a multiple of their length).

Builder of my house drove two right next to each other. Pointless.

 

I think he stopped to clean his pants.

 

I'm aware of that. But I'm not sure if there are any ground rods right now. So a couple more, even if they happen to be close to existing ones, won't hurt anything.

 

That could certainly be learned pretty quickly by borrowing or renting a clamp-type ground tester, or just renting an electrician for 15 minutes to bring hers. Would be a fairly interesting thing to learn....

 

As an early adopter of the 2011 Nissan LEAF, this was a major problem, and it wasn't necessarily lightning strikes but the power outage that can happen. The GE Wattstation, of which I own one, initially was blamed, as a large number of problems occurred with these EVSEs, but it had happened to other brands too. I think it turned out that Nissan didn't have one component of the onboard charger robust enough to withstand an event where the power went out and quickly came back on, but I don't think Nissan ever admitted this was the fault, nor did Nissan ever exonerate the GE Wattstation, although I believe with near certainty that GE wasn't at fault. I remember several people had their onboard charger replaced, but it was replaced under warranty. I thought it was an updated part also, but I think Nissan then changed the software control too so that such an event didn't destroy the charger.

So either way, I strongly attempt to never have the LEAF or now the Prime plugged in even when it is raining.