Comments by "ke6gwf - Ben Blackburn" (@ke6gwf) on "Ground Wire Explained" video.

I held my breath through this, waiting for the big fatal mistakes, but I didn't find any! Good job lol There was one minor one and an oversight. The ground rod isn't only to dissipate static, it's what references the entire ground and neutral system to be Equal Potential with the dirt, and also the water pipes, building frame etc. You didn't mention how the ground rod is also bonded to the water pipes for this reason. And when you said that the fault current will travel back to Source via the ground wire INSTEAD OF through the earth, that's incorrect, it takes both/all available paths, so some current will flow through the earth all the way back to the power plant itself. It will be very small, and if you hook a wire to a ground rod and connect a hot wire to it, you won't trip a regular breaker so little current flows, but SOME current does flow. But still, you give a better explanation than most people ever have lol
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The long version... lol In order to have current flow, you have to have a complete circuit between the power source, through the wires, and back to the other side of the power source. The ground wire is connected at one end to the neutral conductor, thus to one side of the power source, but it has no connection to the other side of the power source, and also no connection anywhere else to the neutral wire, and so no current can flow. This is actually exactly why the ground and neutral are only supposed to be Bonded at a single location, because if you had the ground wire connected to neutral at the main panel and also at an outlet you would get some current flow on the ground wire, because it basically becomes part of the neutral circuit, and that's not good! For one thing when you have current flow in a conductor, due to resistance you have differences in potential along the wire, and so some parts of the ground wire would now have a voltage difference when compared to say the water pipes, leading to shock hazards. This is part of the reason for the ground rod at the house, which will also be bonded to the water pipes, it's to achieve what's known as Equal Potential, where the neutral wire, and the ground wire, is at the exact same voltage as the water pipes and the dirt. And the ground rod at the transformer bonds the split phase windings to force one side of the transformer to be at the same potential as the earth. If you leave the neutral floating on a transformer, then you get 120v or whatever between the terminals, but you don't have one that's at 0v in reference to the ground, it floats. One site I was working on some industrial controls in an equipment room, and I was there after dark one day and discovered that there was 110v on the ground buss in the plc cabinet after I melted the end off a screwdriver lol I found that there was 0v from the "Hot" wire to grounded objects like water pipes, and 110v on the neutral and ground wires. I started testing but didn't find anything that night, so the next day I was going to start tracing the whole system back through the breaker boxes, but when I got there, everything was correct! I was confused, until a later day I was there late and around dark I heard a loud clunk, and curious I checked, and the voltage had flipped. Then I realized that some big outdoor lights were powered off the 110v panel, and so I started turning breakers off, and finally discovered that when I turned the breaker for one of the lights on, the voltage flipped. I discovered that the light circuit was dead shorted when the photocell energized it, so I disconnected it until it could be replaced. The room was served by a 3 phase feed, and they had put a transformer in the room to derive 110/240, and when I pulled the panel off, sure enough, the electrician who installed it had not bonded the neutral, so it was floating. That meant that when the "hot" side was shorted to ground, rather than tripping anything, it just referenced the whole transformer, and everything on the sub panel, so that hot was at Ground potential, and thus ground and neutral were now at 110 v to ground. I called the site rep over the next day and told him the problem, but he tried to tell me I was crazy, so I put the meter between the ground buss and the metal building, and took a test lead and hooked it to a screwdriver and the metal building, and jabbed the screwdriver into a live outlet with him yelling at me to stop, and then told him to look at the meter... I had to walk him through bonding and what was happening, but finally he agreed to call their electrician to come in and wire the transformer properly.
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@zlmdragon. you would be surprised how many electricians don't properly understand how grounds work.
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@gandalf1783 if you are insulated and touch a hot wire, nothing happens. Just like a bird sitting on a power line. However, moisture is present in a lot of things, and most shoes are not completely insulating (sweat from the foot combined with pinholes in the sole etc), and so electricity can often find ways back to Source. For instance, if you are standing on bathroom floor after someone took a shower, the floor might have enough moisture on it to make a current path to a ground-bonded water pipe. You can also simply touch both terminals on an outlet. Or on carpet, if the humidity is high enough there might be some conductivity, or maybe you are kneeling on a nail beneath the carpet and the board has some moisture because the crawl space has high humidity, and the board is grounded to the damp concrete foundation. However, if you are wearing dry shock hazard shoes which have a dielectric barrier in them with no pinholes, or you are standing on a dry rubber anti shock mat, a clean and dry fiberglass ladder or plastic stool, then you can touch a hot lead with no shock, because there is no where for the current to go. All of the situations I mentioned before are very high impedance circuits, but it takes so little current to be dangerous to us that we can still get that shock. Now, I have gotten a lot of shocks in my life, between faulty equipment (not my fault) and working with electricity (my fault lol), and most of them were more straight forward, standing on wet surfaces, or touching both sides of a circuit, like the time my hand slipped on a large motor starter overload reset button and I punched across the 3 phase 480v terminals with my knuckles. I was actually standing on wet metal when it happened, but I had dry boots on so the only shock I got was between phases across my knuckles. I also was in the habit when I was working on open control panels like that to keep one hand behind my back, which may have saved my life that time, because if my other hand had been holding the cabinet door at the time it would have been much worse. I had an old electrician friend who used to never put cover plates on at his place so he could test the power easily if something went out, and he had to lick his fingers to be able to feel 110 v lol And usually he had to touch across both terminals or touch something grounded, because he would not be grounded standing on dry dirt or concrete. But it's hard to tell for us normal people whether what we are standing on is indeed dry enough to insulate us from ground.
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It looks like the TT system is using the ground rod basically to dissipate static and keep the cabinets at equal potential to the building frame, water pipes etc, and doesn't serve as a fault current path to trip overload style breakers, which is a primary purpose for it in North America. It looks like TT relies on smart breakers to detect faults between legs, rather than relying on too much current. This is a good thing, and I tend to put AFCI/GFCI (the US equivalent lol) in whenever I can since I like the additional protection they give, but it is also more expensive and complicated to do a TT system than just a standard US bonded neutral and overcurrent fuse/breaker protection system. And I am believing that the reason that it runs to a ground rod and isn't also bonded to the neutral is because the breakers are not designed to trip from that current path, and so by not bonding it you prevent high current to ground, when all you need is enough current leakage to trip the RCD detector.
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@stevenhargreaves9897 you are correct that electrons take all available paths, which is why the ground and neutral circuits are only allowed to be bonded at a single point, otherwise the ground wire would have varying potential along its length since it would be a parallel current path. So yes, a fault circuit that includes contact with the earth as well as the ground wire will return some current through the earth, and so the statement in the video is inaccurate. In practice it doesn't make much difference, because even with a salt water soak, the impedence of the soil will be so much higher than a copper wire that negligible current will flow, but it may be enough current to stop a heart, so that's why we use GFIs etc. So yes, that should be worded differently, but it's relatively minor in the scheme of things. The main purpose for the ground wire is to get a high enough fault current to trip the breaker, because through the earth is basically never enough current to trip a breaker and stop a fault.
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@ivanfenis1221 it's the opposite. Proper equipotential grounding makes things much safer for human meat bags, because it makes it more likely for the circuit breaker to trip instantly, rather than having fences and frames at high voltage for people to touch.
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@endersonkliverthybarra9747 which is why I said he did a good job, and then ADDED a couple of key points he didn't include in the video, so that people reading the comments would get the full picture.
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@ivanfenis1221 yes. If a fence around a substation for instance is not well grounded, a live high voltage wire could fall onto it and energize the fence. And then when the utility worker arrives at the substation to find out why people are without power, they get electrocuted when they touch the gate. On the other hand, if the fence and all metal items in the substation are grounded in what's known as Eqipotential Bonding and Grounding, then if the live wire falls on the fence, it is a dead short to ground and either burns through the wire, or trips the breakers. It happens sometimes that power lines will fall down on top of a wire fence on wooden posts going across a farm and start a fire, and a firefighter will get electrocuted miles away if they touch that fence before the utility gets there to shut the power off. In a home situation, it's not the "ground rod" that makes the breaker trip, but rather the Grounded Conductor being bonded to the neutral to provide a low impedance path back to the Source. The ground rod is there in that situation to bleed off static charges and to reference the system 0 volts to ground, but it's that zero volts to ground reference that's important! If you had a bad ground rod connection, you could theoretically have the water pipes at 110 volts in reference to the earth from a short circuit, without tripping a breaker. If you were in the house you might be able to touch the pipes fine, but when you are standing on the dirt and go to turn the hose off, you could get a shock.
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@ivanfenis1221 it's confusing lol There's a difference between the Grounding Conductor and the Grounded Conductor (Ground and Neutral). Connecting the ground and the neutral (green and white) together is called Bonding. The Ground wire is also connected to the grounding rod in the earth. If you have enough ground rods you can actually use the earth as the return path to source. Some rural power grids only have a single wire on the pole, and use Earth Return at the Transformers, but a normal single ground rod at a house won't conduct enough electricity on its own to trip a breaker, which is why it's also "Bonded" to the neutral.
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@ivanfenis1221 that circuit loop is one that would potentially be involved, but if a person touches a live wire, the current flows through them to Earth, and returns directly to the grounding system at the power plant, as well as to every grounding rod and system for every substation and transformer on the circuit. Electricity DOESN'T take the path of least resistance, it takes ALL paths of conduction. And while you can hook an extension cord from a 20 amp household breaker directly to a ground rod and not enough current will flow to trip the breaker (only a few amps will flow at 120 v with typical soil conditions), it's more than enough to kill you. Which is why the substation fence would have ground wires and straps all along it, so that the voltage in the fence can never be different than the voltage of the soil next to the fence, even if a hot wire was sitting on it. Basically provide a bigger pipe for current to flow into the earth, than the wire above has to flow current into the fence.
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