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Hey, hey, okay, we got it. All right, so I am Giggs. I am the founder of Pound Electronics on Freenode.

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It's Pound Pound Electronics, but it'll afford you.

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So we're going to talk about what is ground, and we're also going to talk about some transmission line theory stuff toward the end there.

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So is this ground? I would say not.

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So I found this picture on the internet. Clearly there's some confusion about what grounding is, what grounding does.

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And this is obviously not accomplishing anything.

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So what? Not legit, not legit at all.

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So ground is a concept by which we measure our voltage.

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Voltage only exists as defined between two points.

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There's no such thing as voltage that exists by itself.

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So you have zero volts, and that's just whatever you say zero volts is.

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And anything else is not zero volts if it's got a different voltage.

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Voltage is also known as potential, and that's a good word,

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because it's the potential of the voltage.

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It's the potential between two different objects.

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Just like, you know, you have like gravitational potential.

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Gravity only really makes sense between two objects.

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Voltage is the same way.

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So here's some symbols and names that you might see for ground.

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The first one's pretty common.

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You might see the second one, the third one on some electronics things.

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These words are not very good words.

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I mean, obviously chassis ground is the chassis.

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But these are not very good words to use for ground.

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Sometimes you also see this little.

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It's upside down T for ground.

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So better terminology for ground is to just split it into safety grounds,

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which do not normally carry current,

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and working grounds, which do carry current.

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And really, those are the two meaningful distinctions in ground.

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So here's how you blow $1,000 in five seconds.

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Hooking up your oscilloscope ground clip to something that has a potential

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with relation to ground.

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And if you hook it into the wall, that will blow up your oscilloscope ground lead,

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or possibly worse.

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So you see in this here, we got the ground clip hooked up to a 100-ohm resistor.

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We're reading the signal across that resistor.

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But in effect here, you're clipping your ground,

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because the signal ground in the oscilloscope is attached to the chassis ground,

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which is attached to the wall plug ground.

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So you're grounding out through that 100-ohm resistor, 200 or 2.3 amps or so is going to go

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through.

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That fuse, in this case, the fuse might save you, but this is not a good idea.

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So the solution to this, or this is a little diagram here, it's crudely drawn.

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But you can see that the scope signal ground goes right to the breaker box,

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and the neutral and ground in your wall plug come together at the breaker box.

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So it's the same as connecting live and neutral, same as making a short circuit.

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So one solution to this is to just use a battery powered oscilloscope.

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That way, it's not referencing.

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It's referencing your wall ground.

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You're isolated, and you can get a little portable oscilloscope that's on a battery.

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Then it doesn't matter where you clip to, because you're just measuring the voltage

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between the probe and the probe ground, and your scope itself isn't referenced.

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Another way to do it is to just break the ground pin off your scope.

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That's not a good idea, because then if you clip your ground to something hot,

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the chassis of the scope is going to be hot.

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The battery powered ones are generally insulated on their chassis,

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so you're not going to get a zap from touching them.

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But yeah, so battery, breaking the ground pin.

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Third option is isolation transformer.

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This only works if you are using a low powered thing under test here,

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because an isolation transformer bigger than about 200 watts is huge.

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So generally, for 200 watts or less, you can use an isolation transformer for the thing you're testing,

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and that isolates it as well.

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It breaks that path between the live and the ground.

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Oh, whoop.

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Oh, my gosh.

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Oh, my.

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All right, or you can use a fed isolated probe.

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These are kind of expensive, but they have an amplifier in them,

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and they're measuring just that signal between the probe,

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none of the rest of the circuits involved, and you can get those for your scope.

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So what does this do?

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I mean, going back to that first picture, what does this ground rod in the ground actually do?

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Most of you all have probably seen this.

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So I've got a demo to help explain that.

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If the demo works, this is the iffy part here, and I also can't see my mouse down here.

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All right, so this is called Faustad, I'm sorry, this is called Faustad Circuit Simulator.

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It's a pretty neat little simulator.

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You can download it in Java.

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Oh, crap.

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Josh, what's wrong with your mouse?

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Anyway.

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All right, so let me just go over the basics here.

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So the dots show the flow of the current, and the red is negative voltage compared to the arbitrary ground that we've picked,

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and green is positive voltage.

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So this is a little LC tank oscillator.

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I'm going to try, I'm having to use the web version of this because the Java version did not run.

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I hope you don't have any porn-like anything.

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You can't see it anywhere obvious, right?

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All right.

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Not obvious.

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Yeah.

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Y'all want to do find?

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Find slash?

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All right, so this is a little simulation of your actual home wiring.

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Oh, it loaded.

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Okay.

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So we're just going to have to do it like this.

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All right, so this is sort of what's going on in your house.

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You've got this transformer up here in the upper left.

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Is this?

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the transformer on your pole or buried in your yard in some places. Then on your side

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of the transformer, you've got 240 volts between the two lives. And then the neutral is in

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the middle. So in the U.S., that gives you 240 between the sides, 120 between the middle

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and either one of the sides. And that little interleave pattern, if you look over there

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on the, let's see if I can point. Ooh. I don't know why I'm clicking. Why am I clicking?

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All right. This little interleave here is the breaker box. So they actually do interleave

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like that. And the reason for that is that they can make a breaker twice as wide, and

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that makes it 240. Or they can make a breaker skinny, and that makes it 120, because it's

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either connecting to one side or to both sides. And then the neutral ground bar is

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the center of the transformer. But if you notice there, that ground, why is it moving?

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All right. It shouldn't be moving. So the ground rod isn't really doing much of anything.

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And in the Java version, it doesn't even show any current moving on it. But either way,

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the ground rod is not doing much of anything. Now, remember we talked about safety grounds

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and working grounds. The, we do have some leakage. I'm not sure. In this Java version,

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it doesn't show any movement on the safety grounds. But these boxes that go around everything

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here, those would be the safety grounds, like the chassis. The working grounds are these

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ones that are carrying a lot of current here.

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So if we have a ground fault, how much does the thing completely negate my point? So now

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we have a ground fault here.

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Now, the safety ground is carrying current, and that's the only time that does. But if

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you notice the ground rod is not doing anything. It's not doing anything under fault conditions.

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It's not doing anything under normal conditions.

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If you disconnected it, not much would happen.

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It doesn't do a whole lot because that fault is completely contained within your house's

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transformer.

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That neutral ground bar where your grounds come together to the neutral is where you're

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short-circuiting.

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If you have a washing machine with a metal chassis, a hot wire comes unattached, it touches

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the chassis, it's a short-circuit through the neutral ground bar through the transformer

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in your house.

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Nothing to do with the ground rod.

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What does the ground rod actually do?

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Why is it there?

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We have a little lightning simulator here.

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This is 10,000 volts and it's just out there in relation to ground and we'll add that in

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maybe.

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There it goes.

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Now we see the ground rod doing something.

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We've got an external static charge.

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That is in relation to ground.

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It's not self-contained within your house's transformer.

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The lightning or any static buildup in your house does filter out through the ground rod.

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It gives it a potential reference to keep the ground near your house at the same reference

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voltage as the zero volts that we defined as the center of the transformer.

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But it really does not do much most of the time other than exist to make sure that your

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house doesn't float in relation to the ground and to shunt off any kind of lightning or

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static charges.

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Does that make sense to everybody?

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Good.

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The ground rod is basically the least important part of your grounding system.

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This neutral ground bar is what handles fault currents.

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It's what's handling all of that sort of thing.

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Now we're going to shift gears a little and talk about transmission lines.

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Oh, crap.

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What did I do?

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Josh?

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I closed what?

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You minimized it.

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Did I?

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Oh, I minimized it.

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Yeah.

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Where is it?

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You closed it.

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You totally closed it.

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Well, then what is this?

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That's that.

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Well, that's what I want.

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Oh.

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For now.

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Maybe.

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Is it going to work?

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Yeah.

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Yeah.

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Yeah.

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Yeah.

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Is it working?

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All right.

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All right.

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So now let's talk a little bit about transmission lines.

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So there's two different ways that transmission lines generally work.

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They're single-ended, in which case one side of the transmission line is defined as zero

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volts or ground.

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And then there's balanced or differential signaling in which there isn't really a ground.

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The pulses are symmetrical in relation to each other.

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And the reason that that's done is because if there is common mode noise in the bottom

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picture, you see the noise, it gets subtracted from itself.

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The input pulse is one positive pulse, one negative pulse.

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You subtract a negative from a positive, you get a stronger positive because you flip

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the signs.

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But when you have noise on both sides, you subtract them, they cancel out.

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So differential signaling can cancel out common mode noise.

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Am I losing anyone?

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All right.

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So the way that you help make sure that the noise is common mode is that the wires are

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generally twisted together.

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They aren't necessarily shielded, which is why you see unshielded twisted pair in things

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like Ethernet.

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In single-ended, you're more likely to see something like coax, where the shield is

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sort of acting as a Faraday cage.

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Both of these are generally built as controlled impedance lines, which is something we'll

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get to in a minute.

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But that just means that they carefully make the wires so that it's consistent along the

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whole length, that it's not varying a lot.

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This is a little block diagram of something that's handling a balanced signal.

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You see there is two grounds here.

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Then they've got two different ground symbols, a signal ground and a chassis ground.

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They do tie together right there.

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But you see that first op amp, that triangle symbol, that's subtracting them.

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It does something to them.

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And then they've got two op amps pushing and pulling the signal like this.

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To output it.

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So it's a little block diagram of how a differential or balanced signal would work.

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So now we're going to talk about getting high frequency.

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I'm not going to read it.

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You can read it.

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When you start to get a wavelength that is short compared to your wire, or when your

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wire starts to get long compared to your wavelength, then transmission line effects start to matter

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more.

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So if your frequency is low, which means your wavelength is long, then transmission

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line effects don't matter as much.

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And you'll see what I mean here in a minute.

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So at 60 hertz, one full wavelength would be 5,000 kilometers.

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So you're not likely to run into transmission line effects at 60 hertz.

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At 30 kilohertz, it's 10 kilometers.

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So that means that transmission line effects, all that fancy transmission line stuff, doesn't

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really apply to audio frequencies.

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Audio frequencies are mainly dealing with resistance.

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And that's about it.

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Because they're not getting a lot of transmission line effects.

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Because 10 kilometers wavelength means that our wires are all real short compared to the

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wavelength.

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At 1 megahertz, we start to get to where we might have a wire long enough for transmission

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line effects to come into play.

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That's 300 meters.

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And at 100 megahertz, we're down to just 3 meters where we have to start worrying about

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transmission line effects.

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So what is a transmission line effect?

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Well, a transmission line, you have a circuit voltage is only something in relation to

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another voltage.

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So we have to look at both sides.

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We can't just look at our signal and not look at our ground or vice versa.

244
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We have to look at both wires.

245
00:13:56,920 --> 00:14:01,180
And those wires, in relation to each other, their physical arrangement is going to determine

246
00:14:01,180 --> 00:14:01,900
a capacitance.

247
00:14:02,260 --> 00:14:07,080
If you all are familiar, a capacitor is just two metal plates hold a charge in relation

248
00:14:07,080 --> 00:14:07,740
to each other.

249
00:14:07,800 --> 00:14:11,520
How far apart they are, how close they are, what's in between them, determines the

250
00:14:11,540 --> 00:14:11,800
capacitance.

251
00:14:11,800 --> 00:14:13,420
It determines how much capacitance there is.

252
00:14:13,700 --> 00:14:17,900
So when you're building a wire, you're also building a capacitor between, or sorry, when

253
00:14:17,900 --> 00:14:22,020
you're building a cable that has two wires, you're building a capacitor as well.

254
00:14:22,140 --> 00:14:24,340
It's just a long stretched out tubular capacitor.

255
00:14:24,740 --> 00:14:30,040
So you have to control the distance between the wires, control the material between the

256
00:14:30,040 --> 00:14:32,980
wires to control the capacitance between the wires.

257
00:14:33,180 --> 00:14:37,480
And then every wire that has current flowing through it is also an electromagnet.

258
00:14:37,500 --> 00:14:38,660
You all may be familiar with that.

259
00:14:39,220 --> 00:14:41,520
Anything with current flowing has a magnetic force.

260
00:14:41,540 --> 00:14:43,660
So wires also have inductance.

261
00:14:44,340 --> 00:14:49,200
So between the inductance and the capacitance, that looks like a resistance.

262
00:14:49,500 --> 00:14:50,740
It's technically an impedance.

263
00:14:51,220 --> 00:14:52,900
But it looks like a resistance.

264
00:14:53,280 --> 00:14:57,920
And if the wire or the cable is consistent along its whole length, it can be said to

265
00:14:57,920 --> 00:15:04,280
have a characteristic impedance, which is what the cable looks like for it until infinity,

266
00:15:04,520 --> 00:15:05,920
assuming it's terminated.

267
00:15:06,540 --> 00:15:11,520
So we're going to maybe, maybe get this other demo on.

268
00:15:11,540 --> 00:15:11,700
It's not working.

269
00:15:12,680 --> 00:15:14,040
Josh, where'd the browser go?

270
00:15:14,180 --> 00:15:14,720
There it is.

271
00:15:16,460 --> 00:15:18,940
Does anyone have any questions while I'm playing with this?

272
00:15:19,620 --> 00:15:21,840
Trying to get the browser back up.

273
00:15:23,820 --> 00:15:25,380
The neutral ground.

274
00:15:25,600 --> 00:15:26,140
Yeah.

275
00:15:26,240 --> 00:15:28,140
The five slides ago.

276
00:15:28,360 --> 00:15:28,560
Yeah.

277
00:15:29,290 --> 00:15:34,060
The outside of the house ground that shunned off electrical for .

278
00:15:35,280 --> 00:15:35,820
Yeah.

279
00:15:35,960 --> 00:15:37,440
Thor lightning.

280
00:15:37,800 --> 00:15:39,080
What is that?

281
00:15:39,440 --> 00:15:41,240
What is it in your house?

282
00:15:41,240 --> 00:15:41,540
All right.

283
00:15:41,560 --> 00:15:44,200
So like your plug has three, three, three.

284
00:15:44,340 --> 00:15:44,560
All right.

285
00:15:44,560 --> 00:15:46,000
So you got live, neutral, and ground.

286
00:15:46,240 --> 00:15:46,500
Yeah.

287
00:15:48,060 --> 00:15:49,420
So live, neutral, and ground.

288
00:15:49,500 --> 00:15:51,380
Those three wires go back to your panel.

289
00:15:51,740 --> 00:15:55,900
At your main panel, if you have a subpanel, this isn't necessarily true, but at your

290
00:15:55,900 --> 00:15:58,620
main panel, the neutral and ground just connect together.

291
00:15:58,860 --> 00:15:59,240
Okay.

292
00:15:59,360 --> 00:16:01,840
So it's just like a second path for neutral.

293
00:16:02,000 --> 00:16:04,200
But it's a path that doesn't carry current.

294
00:16:04,520 --> 00:16:06,900
So the neutral ground is the working ground.

295
00:16:07,280 --> 00:16:10,360
The safety ground, the big longer pin.

296
00:16:10,360 --> 00:16:12,340
The safety ground doesn't carry current.

297
00:16:12,440 --> 00:16:15,860
So you got a working ground and the safety ground on your outlets.

298
00:16:16,120 --> 00:16:21,120
And they're basically a parallel path, an alternate path that the current can take if

299
00:16:21,120 --> 00:16:23,760
something shorts out to the safety ground.

300
00:16:24,180 --> 00:16:31,360
And that can be useful as well because like ground fault interrupters will detect when

301
00:16:31,360 --> 00:16:35,820
the neutral current doesn't match the live current, which means that something is going

302
00:16:35,820 --> 00:16:37,900
out the ground where it's not supposed to be going.

303
00:16:38,080 --> 00:16:39,580
It's used in the back door.

304
00:16:39,580 --> 00:16:41,480
When it should be used in the front door.

305
00:16:41,740 --> 00:16:42,520
Common problem.

306
00:16:44,900 --> 00:16:45,420
All right.

307
00:16:45,480 --> 00:16:47,100
So let me get this going again.

308
00:16:51,040 --> 00:16:52,660
Sorry if I'm breathing on the mic.

309
00:16:52,780 --> 00:16:55,020
I've kind of got to stand a certain way here.

310
00:16:56,040 --> 00:16:56,540
All right.

311
00:16:56,560 --> 00:16:57,720
I've almost got it.

312
00:16:58,000 --> 00:17:00,000
And all right.

313
00:17:00,020 --> 00:17:00,560
We got it back up.

314
00:17:01,160 --> 00:17:03,400
So I can actually, maybe if I don't break this circuit.

315
00:17:03,520 --> 00:17:04,900
This is an LC tank circuit.

316
00:17:05,160 --> 00:17:08,920
So you can kind of see how an inductor takes a little while to charge up.

317
00:17:09,700 --> 00:17:11,900
And then it will ring with this capacitor.

318
00:17:12,140 --> 00:17:16,920
This is actually a basic oscillator that is used quite a bit in radio and everything.

319
00:17:17,860 --> 00:17:20,280
So an inductor and capacitor like this.

320
00:17:20,460 --> 00:17:22,640
It's not too different from what we were talking about.

321
00:17:23,140 --> 00:17:23,820
But let me get.

322
00:17:28,180 --> 00:17:30,540
Let's take a look at this example first off.

323
00:17:31,020 --> 00:17:31,800
This is.

324
00:17:31,960 --> 00:17:33,660
Let me open it and reset it.

325
00:17:34,000 --> 00:17:38,900
So I said the transmission line effects only really matter when you're in a

326
00:17:38,900 --> 00:17:44,860
regular pulse is getting long in relation to your wire length.

327
00:17:45,040 --> 00:17:47,580
Or your wire length is getting long in relation to your pulse.

328
00:17:47,900 --> 00:17:49,500
This is actually just a very.

329
00:17:49,760 --> 00:17:52,720
If you look at the time step down there, five picoseconds.

330
00:17:52,840 --> 00:17:55,000
So we're looking at this on a very small time step.

331
00:17:55,340 --> 00:17:58,300
This is just turning a light bulb on basically.

332
00:17:59,220 --> 00:18:02,000
And you notice the power just doesn't start flowing.

333
00:18:02,700 --> 00:18:04,240
It bounces back and forth.

334
00:18:04,440 --> 00:18:07,100
It homes in on the actual amperage.

335
00:18:07,300 --> 00:18:08,500
And this is just a regular.

336
00:18:08,500 --> 00:18:10,020
Regular old circuit.

337
00:18:10,300 --> 00:18:14,180
You know it's going to vary a lot because our wires like in our wall aren't impedance controlled.

338
00:18:14,500 --> 00:18:15,820
So we couldn't hit this exactly.

339
00:18:16,300 --> 00:18:21,300
But you see it actually hunts down to the actual voltage.

340
00:18:21,380 --> 00:18:23,280
We got 100 volts and 100 ohms.

341
00:18:23,320 --> 00:18:25,440
I think it's going to land on one amp eventually.

342
00:18:26,040 --> 00:18:28,900
But this is all happening in such a short time scale.

343
00:18:29,840 --> 00:18:32,760
We aren't even at 700 nanoseconds yet.

344
00:18:33,400 --> 00:18:36,000
So it doesn't matter because it looks like it's instantaneous.

345
00:18:36,000 --> 00:18:38,720
Because we're looking at it slower than this is happening.

346
00:18:39,220 --> 00:18:44,720
So that's why you can say if your frequency is high enough then it starts to matter.

347
00:18:44,860 --> 00:18:48,720
Because you're looking at it on a short enough time scale that you can actually see this happening.

348
00:18:53,300 --> 00:18:54,980
So I got another demo here.

349
00:19:02,420 --> 00:19:05,980
So the characteristic impedance.

350
00:19:05,980 --> 00:19:08,820
As defined by the capacitance and inductance.

351
00:19:09,640 --> 00:19:12,920
What we want to do is we want to put a resistor on the end of that line.

352
00:19:13,020 --> 00:19:16,020
That makes it look like that impedance continues out to infinity.

353
00:19:16,520 --> 00:19:19,060
And when we do that there isn't much reflection.

354
00:19:19,460 --> 00:19:23,000
This thing gives you a little shadow of a reflection even when it's impedance matched.

355
00:19:23,340 --> 00:19:24,600
But there isn't much reflection.

356
00:19:24,920 --> 00:19:28,580
If there is an impedance mismatch on the end of the line.

357
00:19:30,360 --> 00:19:33,180
The signals actually start bouncing off the end of the line.

358
00:19:33,440 --> 00:19:35,400
And then you get a very noisy signal.

359
00:19:35,400 --> 00:19:38,660
This is why you always need to terminate a lot of these buses.

360
00:19:38,860 --> 00:19:40,440
Or have some self termination.

361
00:19:40,820 --> 00:19:44,120
Because the impedance needs to appear to continue on to infinity.

362
00:19:44,420 --> 00:19:46,560
Makes the wire look like it's infinitely long.

363
00:19:49,340 --> 00:19:51,060
And I've got one more demo.

364
00:19:51,680 --> 00:19:52,960
How am I on time?

365
00:19:53,540 --> 00:19:54,540
Is anyone going to have time?

366
00:19:55,720 --> 00:19:56,480
20 minutes.

367
00:19:56,800 --> 00:19:58,040
Oh we've got plenty of time.

368
00:19:58,400 --> 00:19:58,960
Alright so.

369
00:20:00,340 --> 00:20:00,820
Yes.

370
00:20:01,240 --> 00:20:04,060
Does the resistance of the matter.

371
00:20:04,800 --> 00:20:07,220
Are those 75 ohm resistors?

372
00:20:07,680 --> 00:20:13,200
The reason that this has to match the characteristic impedance of the line.

373
00:20:13,540 --> 00:20:17,380
So we've got a 75 ohm transmission line with a 75 ohm resistor.

374
00:20:17,740 --> 00:20:21,440
75 ohm is actually a common line for like television coax.

375
00:20:23,380 --> 00:20:29,540
And that characteristic impedance is based on the construction and the materials that the cable is made of.

376
00:20:29,660 --> 00:20:34,000
Like the plastic that's actually in the coax helps define that.

377
00:20:34,060 --> 00:20:36,560
And they handle all that at the factory.

378
00:20:36,700 --> 00:20:40,120
But they can say that the characteristic impedance is 75 ohm.

379
00:20:40,180 --> 00:20:42,660
So if you stick a 75 ohm resistor on the end of this.

380
00:20:42,760 --> 00:20:44,540
Things shouldn't bounce off the end of it.

381
00:20:44,760 --> 00:20:47,040
At high enough frequencies for it to matter.

382
00:20:48,000 --> 00:20:50,480
So I have a 75 ohm line here.

383
00:20:50,560 --> 00:20:51,980
And a 500 ohm line here.

384
00:20:52,220 --> 00:20:54,360
So that's why they're terminated like that.

385
00:20:55,520 --> 00:20:58,860
If we take off the termination in the middle of the line here.

386
00:20:58,980 --> 00:21:01,340
This is actually like an impedance matcher.

387
00:21:01,400 --> 00:21:01,860
It's got.

388
00:21:02,480 --> 00:21:03,020
You know.

389
00:21:03,020 --> 00:21:05,580
It's got 75 on this side and 500 on this side.

390
00:21:05,980 --> 00:21:07,620
So if we take this off.

391
00:21:07,680 --> 00:21:08,660
The signals still go through.

392
00:21:08,780 --> 00:21:10,660
But we're getting reflections on the first side.

393
00:21:11,280 --> 00:21:12,660
So not quite as messy.

394
00:21:12,840 --> 00:21:13,980
But it's still not good.

395
00:21:21,100 --> 00:21:22,940
And which one haven't we done?

396
00:21:23,040 --> 00:21:23,360
Lightning.

397
00:21:24,160 --> 00:21:24,660
All right.

398
00:21:24,680 --> 00:21:26,420
So this is an interesting little demo.

399
00:21:26,700 --> 00:21:27,740
You remember I said.

400
00:21:28,400 --> 00:21:31,060
Even at lower frequencies.

401
00:21:31,060 --> 00:21:34,080
Lightning has generally got a pretty fast rise time.

402
00:21:34,260 --> 00:21:36,100
It's surging pretty quick.

403
00:21:36,260 --> 00:21:38,300
So it can be viewed as a higher frequency.

404
00:21:40,120 --> 00:21:42,180
But in the short scale.

405
00:21:42,300 --> 00:21:45,420
You can actually get reflections off of a surge protector.

406
00:21:45,840 --> 00:21:46,720
With lightning.

407
00:21:47,000 --> 00:21:49,020
So you can almost get a secondary surge.

408
00:21:49,180 --> 00:21:52,580
From the lightning reflecting back off your surge protectors.

409
00:21:52,840 --> 00:21:55,420
So if you have anything important.

410
00:21:55,600 --> 00:21:57,160
Try to put a surge protector on each one.

411
00:21:57,420 --> 00:22:00,800
So that they don't reflect back and surge your other devices.

412
00:22:00,800 --> 00:22:03,100
So let's do this.

413
00:22:03,620 --> 00:22:05,000
Let's start the lightning going.

414
00:22:05,660 --> 00:22:06,140
Maybe.

415
00:22:07,240 --> 00:22:08,060
Oh crap.

416
00:22:09,280 --> 00:22:09,920
All right.

417
00:22:12,920 --> 00:22:13,620
There it goes.

418
00:22:13,920 --> 00:22:14,380
All right.

419
00:22:14,380 --> 00:22:15,480
So this is the lightning surge.

420
00:22:16,060 --> 00:22:18,500
We're looking at a very fast time scale.

421
00:22:18,540 --> 00:22:19,400
Or very slow.

422
00:22:19,480 --> 00:22:20,760
Depending on how you look at it.

423
00:22:21,240 --> 00:22:21,780
You know.

424
00:22:21,820 --> 00:22:23,800
This is all happening in pico seconds.

425
00:22:24,060 --> 00:22:24,620
Nano seconds.

426
00:22:24,820 --> 00:22:25,620
This is happening quickly.

427
00:22:26,420 --> 00:22:27,020
All right.

428
00:22:27,040 --> 00:22:28,220
So let's say that the MOV.

429
00:22:28,700 --> 00:22:30,520
This is the way a surge protector works.

430
00:22:30,520 --> 00:22:31,800
It basically shorts it out.

431
00:22:32,480 --> 00:22:36,160
So when it detects a voltage over a certain level.

432
00:22:36,280 --> 00:22:38,260
It basically shorts out your live and neutral.

433
00:22:38,480 --> 00:22:40,360
Which is why a lot of them burn out.

434
00:22:40,580 --> 00:22:41,960
And if they fail.

435
00:22:42,140 --> 00:22:44,260
They generally have a fuse that cuts them off.

436
00:22:44,340 --> 00:22:46,180
To keep them from shorting out your whole house.

437
00:22:47,600 --> 00:22:48,620
So but if you look.

438
00:22:48,740 --> 00:22:50,520
That MOV is now reflecting.

439
00:22:51,340 --> 00:22:53,980
It's reflecting the surge back onto the other device.

440
00:22:54,460 --> 00:22:57,660
And you see the unprotected device went from 10 kilovolts to 19 kilovolts.

441
00:22:58,100 --> 00:22:59,680
It actually amplified the surge.

442
00:23:00,320 --> 00:23:01,440
So this can happen.

443
00:23:01,520 --> 00:23:03,140
It happens on very short time scales.

444
00:23:03,240 --> 00:23:04,120
It may not matter.

445
00:23:04,300 --> 00:23:05,600
But if you have MOV.

446
00:23:05,600 --> 00:23:07,360
If you have surge protectors or what not.

447
00:23:07,480 --> 00:23:08,920
You should have them on every device.

448
00:23:10,120 --> 00:23:13,540
So that you don't get these potential reflections hitting your other devices.

449
00:23:14,580 --> 00:23:18,240
So and also it helps to have a surge protector at your service panel.

450
00:23:18,340 --> 00:23:20,000
And on your devices.

451
00:23:20,460 --> 00:23:23,760
Because if we were shorting this out at the service panel.

452
00:23:23,920 --> 00:23:25,400
It wouldn't be bouncing around as much.

453
00:23:27,320 --> 00:23:29,240
So got any questions about this?

454
00:23:29,240 --> 00:23:30,060
This one.

455
00:23:30,760 --> 00:23:35,820
So you actually put your devices at more risk by having one or two surge protectors.

456
00:23:35,860 --> 00:23:36,240
Yeah.

457
00:23:36,240 --> 00:23:36,920
In your environment.

458
00:23:37,200 --> 00:23:37,840
It could.

459
00:23:38,240 --> 00:23:40,420
I mean this is a very idealized thing.

460
00:23:40,540 --> 00:23:42,960
In that there's a lot of resistance in your wires.

461
00:23:43,100 --> 00:23:45,140
So it's going to decay down a lot faster.

462
00:23:45,740 --> 00:23:47,500
But in theory yeah you can.

463
00:23:48,120 --> 00:23:51,080
If you have a good surge protector over here.

464
00:23:51,500 --> 00:23:53,460
And you have no surge protector over here.

465
00:23:53,520 --> 00:23:56,200
You can actually send a reflection back to this first device.

466
00:23:56,680 --> 00:23:57,760
And it can actually.

467
00:23:57,760 --> 00:23:59,760
I think it was.

468
00:24:00,000 --> 00:24:02,060
Square D has a paper on this.

469
00:24:02,060 --> 00:24:03,020
A white paper on it.

470
00:24:03,120 --> 00:24:07,300
About reflections from surge protectors actually causing more damage.

471
00:24:07,840 --> 00:24:11,000
Obviously they want to sell you surge protectors for every device.

472
00:24:11,400 --> 00:24:15,560
But you know the simulation bears out that it can reflect.

473
00:24:15,920 --> 00:24:18,060
And it can cause a secondary surge.

474
00:24:18,140 --> 00:24:20,480
That could actually be stronger than the first surge.

475
00:24:20,780 --> 00:24:24,080
Is this only printed for per circuit?

476
00:24:24,240 --> 00:24:25,680
Or for your entire breaker?

477
00:24:26,100 --> 00:24:27,600
Well it's going to reflect.

478
00:24:27,600 --> 00:24:31,640
I guess you know based off of where that.

479
00:24:31,760 --> 00:24:32,940
I mean we're talking about lightning.

480
00:24:33,040 --> 00:24:34,340
So the ground rod is relevant.

481
00:24:35,720 --> 00:24:39,560
So generally I mean it's hard to say.

482
00:24:39,660 --> 00:24:42,240
Because like if you have two wires running right next to each other.

483
00:24:42,320 --> 00:24:43,960
They can induce currents on each other.

484
00:24:44,040 --> 00:24:45,580
Especially when you're talking about lightning levels.

485
00:24:46,000 --> 00:24:47,660
So it's really kind of hard to say.

486
00:24:47,820 --> 00:24:52,420
But the bottom line is you just want to have protection on every important device.

487
00:24:52,680 --> 00:24:54,100
You know things like motors.

488
00:24:54,640 --> 00:24:57,200
Generally you know you might blow a hole in their insulation.

489
00:24:57,600 --> 00:24:59,980
But they can tolerate a lot more than electronics generally.

490
00:25:01,180 --> 00:25:02,460
So just have.

491
00:25:03,160 --> 00:25:05,260
Ideally have protection at your panel.

492
00:25:05,500 --> 00:25:07,100
Protection at your device.

493
00:25:07,600 --> 00:25:09,140
At any important device.

494
00:25:09,460 --> 00:25:11,200
And that's the best you can do.

495
00:25:11,520 --> 00:25:11,660
So.

496
00:25:13,300 --> 00:25:14,260
Any other questions?

497
00:25:17,060 --> 00:25:17,780
All right.

498
00:25:17,820 --> 00:25:19,100
Well I'm Giggs.

499
00:25:19,180 --> 00:25:20,500
I'm over in the hardware hacking village.

500
00:25:21,360 --> 00:25:24,020
We're helping people learn to solder and various other things.

501
00:25:24,200 --> 00:25:25,580
So come see us over there.

502
00:25:25,880 --> 00:25:27,400
And thanks for your time.

503
00:25:28,140 --> 00:25:28,240
Thank you.