Where Does Grounded Electricity Actually Go?
Grounding is one of the most confusing and misunderstood aspects of the grid.
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Errata:
At 10:40, the meter is set to resistance (not voltage). Since current is constant, it is also an indication of differences in voltage, but the script should have been a little clearer.
Current doesn’t flow to the ground; it flows through the ground and back up. If there is electricity moving into the ground from an energized conductor, go back to the source of that conductor and see what’s happening. For the grid, it’s probably a transformer or electrical generator, in either case, a simple coil of wire. And, the electrical current flowing out of the coil has to be equal to the electrical current flowing into it, whether that current is coming from one of the other phases, a neutral line, or an electrode buried in the ground.
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Great channel very very well explained sir!
Got the book and I love it. It is the perfect coffee table book.
Also… that Henson razor is a game changer. I love it.
It would have helped if you spent a bit more time explaining how three-phase AC power works. You glossed over that so quickly I bet most people completely missed the most critical issues here. I’ll admit this is something that could take a video all on its own to explain properly, so go do that!
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@Practical Engineering: at approx 19:30 you mention hopping to limit the chance of step potential – this is no longer the case, at least in the Australian electricity industry. The reason is that a person hopping (one or 2 footed) is very prone to overbalance and accidentelly step or fall, thereby creating the step potential and possibly injuring themeselves as well.
Current training is to keep both feet together and ‘shuffle’ by sliding one foot forward no more than 3/4 of the length of the foot so they stay together, then shifting the other foot in the same manner. In this way, while some ‘step potential’ will potentially still exist it will be small, and the feet / ankles / legs touching provides a path for any currect without transitting through the torso.
Another thing to note is to avoid any sudden ground condition changes where possible – don’t move from dry ground to wet, concrete to grass, etc.
Great content!
Not from the electrical service industry but I was taught another (still different) way of getting away from ground potential: short hopping with both feet together
That’s recommended in electrical training in the US, too. (At least what I had.)
could you attach a wire to the boots, running along the pants to give a lower resistance path?
@Jesse Winn Exactly what I was thinking – can’t we just “ground” the shoes to each other?
I am an electrical engineer (in the US) that designs the grounding grids for substations to limit touch and step potentials. I can confirm that there are tons of calculations & analyses that go into the design, including simulations of worst case faults to make sure there is a near zero chance of injury. However, ground grids are not designed to eliminate potentials, only to reduce it enough to prevent arrhythmia. So if you happen to be at a substation during a ground fault, you may still get zapped, but it won’t be fatal!
Great video Grady!
What is the typical voltage potential at these subs?
An even more difficult concept for many here to understand is Prospective Instantaneous Fault Current.
I have carried out such calculations, although not for a good few years. In the UK we would find the Earth Potential Rise (EPR) and from there calculate the step and touch voltages. The areas where the touch and step voltages were above required levels (referred to as the ‘Hot zone), would require additional earthing and bonding.
How many people do you know who have, “shuffled to safety”. I bet it’s zero.
That’s so cool, @zzzz271! I was always amazed to see how much detail, planning, and regulations/standards you have to adhere to with substation grounding grid analysis and recommendations, just to make sure any human life inside and slightly near the fence line has a chance to survive if a fault occurs. It’s so much more than just welding a bunch of copper grounding grid into the earth and saying “done!”
My electronics professor was explaining 3 phase, 4 wire motors. He had a diagram of the 3phase generator connected to the 3phase motor and kept emphasizing the “4 wire” part of it. Finally a student asked, “where is the fourth wire?” Then he pointed to the ground symbol and added a ground layer to the diagram connecting the generator and the motor.
Three phase may be configured in a “Y” or “Delta” configuration. In Delta configuration there is no phase to neutral connection. At terminations a transformer makes the conversion Y to Delta or vice versa.
How long the class suffered trying to understand until one mind could not take it any longer and had to let his soul get satisfaction in answer form.
Technically, the term “three-phase four-wire” *never* refers to the use of a ground wire, only a neutral wire. If I have a three-phase motor that for some reasons used a neutral wire, as well as a ground wire, it is a four-wire grounded motor (not five-wire).
@M ROr he’s trying to let students think for themselves instead of just blindly accepting everything he says. “Ah yes, three does equal four, because teacher says so.”
If using an ounce of brain power to ask why something seems wrong is considered “suffering,” then it’s no wonder our education system doesn’t work.
I like when ground is Earth. Grounding to the Moon is just so difficult.
You’re just not using the right ladder
@Kiriu XeosaIt’s a step ladder. The real one died.
I wonder if the english artemis astronauts will call the 0v potential on base “mooning”
Smh… Words aren’t toys.
Definitely need a bonding cable run at some point.
As a chemist I’m used to deal with elements exchanging electrons to make things happen, but when it comes to electricity in a circuit & insulation I’m as a smart as a wood door, save from battery cells. Thanks for sharing this with us.
Glad to have a chemist in the room for once.
While you are here, I have been meaning to ask if with the discovery of Quantum “Spin”, have Chemists come up with anything in elemental electron exchange?
I find all the analogies confusing. For me, electricity is easier to understand from first principles. Unfortunately, that involves quantum mechanics, which I guess many feel is too complicated to explain. But only after I saw some videos explaining that electricity is all about the movement of fields and not electrons flowing through the wire like little balls in a pipe, it all clicked. AC is extremely difficult for me to understand if I try to understand it using the traditional analogies.
I must suspect there are similarities. As I understand , in order for an electron to move to a higher orbit it needs to have ‘enough energy’. An electron following its designed path would be the equivalent of a circuit. Insulation refers to the amount of ‘enough energy’ required to exceed its normal path to reach a higher orbit(s). To say, insulation=resistance, the distance of, ‘enough energy’, required to reach higher orbits becomes equivalent to the amount of insulation (resistance) that must be overcome. From Gradys sand example: dry sand offers the most insulation, wet sand offers an amount of insulation, yet salt water offers little insulation. (Different salt((s)) offers different abilities.)
@M R Honestly, after getting to know the basics of quantum in college I figured out it’s just too much for me. The probabilistic behavior of wave-particles in confined orbitals blows my mind every time I think of it, in the end always going back to physics and tons of math (which is a marvelous way to describe and understand reality). Channels like PBS Space Time, Veritassium, The Science Asylum, Physics Videos by Eugene, Arvin Ash and many others would give you a much better response to your question. As far as I know, genius scientists are using the quantum properties to improve computing power. I’m a simple man.
When I started at the power plant, I asked about where all it fed power to. A guy told me it’s pretty much like throwing a cup of water in a stream & someone else pulling a cup of water out down stream. Yea it could’ve been your water, but more than likely, it was a combo of all the tributaries.
So when we are billed to a single power company, how do they know how much of “their” power we actually used?
@Dan Pro That has to do with distribution. Your local utility, co-op, or municipality was the one that installed all of the equipment in order to deliver you power, aka the feeders (power lines), the protection equipment, the substations, and more. They can generate power themselves, or they can purchase their power in order to deliver you yours.
@Dan Pro that’s not a question since both are entirely different entities. a power company is engaged in the field of producing electricity and then also in distributing it. those are separate things. with different revenue flows and balance sheets. more often then not, the distribution even inflicts an internal loss. meaning, would they just sell all their electricity to current brokers instead of the consumers, they’d be better off even.
@Dan Pro Here in the UK, power companies are meant to charge you based on grid usage rather than supply usage as the national grid controls the flow of the entire grid including from all sources, imports and everything. The engineer/TV presenter Guy Martin took over the national grid for a short time in learning how it all works in a series – “Guy Martin’s Great British Power Trip”
But, that’s the UK, so I don’t know how it works for others.
@Dan Pro as far as generators are concerned. They just get a demand from the grid operators, & then try to meet that demand. Renewable & Fossil plants both put power onto the same grid, as the person above mentioned, it’s the transmission operators & distributor’s that actually deliver the power. Sometimes it’s all the same company but such as in my case, our plant is owned by a different company than the one that operates the grid. So customers pay them, & they keep some & pay us whatever the agreed upon price was per Megawatt when we produced it.
Just a small note for 11:34, it’s recommended to shuffle away from a downed power line. If you’re hopping you could fall, and falling next to a downed power line is a really bad idea.
the other directive is, if it’s safe to remain in place, that is always the first option recommended. I.E. if a line falls near your car, stay in the car, unless there is a condition that makes the car a dangerous place, like a fire.
Is the shuffle considered ok because your feet would be very close together and not have as great of a potential between them?
@Sean Roland that’s the theory, yes. keep in mind that as a bag of salt water, you are actually pretty conductive once the voltage exceeds the dielectric strength of your skin and shoes. so if the contact points of your feet are far enough apart that you are more conductive than the ground between your feet, you become a significant current path – so keeping your feet close together avoids that. and doing the shuffle lets you keep your balance more easily than hopping.
@Ken Brownwell the car is safe for other reasons. But I get what you mean. If you have not been shocked and the downed line doesn’t move anymore its unlikely that you will get shocked until you make a mistake
You’re a great teacher Grady. It’s crazy to think that you don’t have professional teaching experience. You’ve taught me so much about the world around me. From full sized dams, to weirs, and even the dynamics of water pipes. It’s amazing how much more interesting the world is when you know how it works. I really appreciate you as a person bro. Thank you
Great video. Despite having a degree in electrical engineering for 21 years, this is the first time someone completely explains the concept of ‘ground’ in all its aspects in one single go.