Duration: 0:00

39 views

0

The idea of the Ground can be complicated and confusing, this video attempts to rectify it.

Normally you would need only 2 wires to power up a light bulb, the positive and the negative wire. The ground wire is a third wire, an unnecessary evil, or is it?

So what is the deal for the ground wire? It's all about safety, an engineer's redundancy, therefore ground is all about safety, and before talking about ground, we need to understand a little about safety. Current kills! While a battery can provide you with a lot of current, it is not high voltage enough for any dummy to get electrocuted by a single battery, but if you connect a sufficient amount of double A batteries in series, it can be lethal. 10 milliamps is considered dangerous. 5 milliamps will give you a tickle, and you may not feel anything for 1 milliamps or less.

Your body or more precisely your skin can be considered as a variable resistor from 1k ohms to 100k ohms. My own measure from my left hand to right hand is actually about 400 k ohms, so 1k to 100k ohms is about the worst scenario.

Assuming you are using 120 volt AC, you could get electrocuted depending on how wet your skin is, calculated using the basic ohm's law. This is a little exaggerated, but when dealing with safety, we always assume the absolute worst possibility.

With that said, let's look closer at an AC socket. The ground is always the middle hole; and the live or hot wire on the right side. The neutral hole is the current returning path of the current source, and it is normally connected to the ground as well, so a very good question would be what is the difference between the neutral and ground wires.

Before understanding what the neutral is, we need to understand how the current is generated. For household main power, it's generated by a coil inside the transformer. The neutral for most wiring is found on the middle tap of the transformer coil. The current source is literally created out of thin air via magnetic induction from the primary coil, so the output coil is floating in the air initially.

Finally, here is how the ground is connected to the neutral. The ground is literally connected to the ground soil. Under normal operation, it's not carrying any current at all. The ground is also connected to any appliance’s outer metallic case, so in case of a leakage, the current returns to the source via the ground, instead of your body. Therefore the ground wire could carry a significant amount of current, and it may also be a physical wire connected from one ground point to another ground point.

Here is a simplification. RX can be any number proportionally smaller than a typical skin resistance of a human body. In case of a leakage, the majority of the current will return to the source via this RX resistor, instead of your body.

In many ways, the ground is similar to a bird preaching on a high voltage wire.

By grounding the leakage high voltage source, it redefines everything around the leakage source on the same ground potential level, making you the bird on the wire literally.

Ground is actually a lot more complex than presented here, but it's a starting point.

----------------
I would give this video script an A-. It's well-structured, informative, and does an excellent job of breaking down a complex electrical concept into understandable terms for a general audience. With the addition of well-placed visuals, it has the potential to be a highly effective educational video.