Why we ground electrical systems (2015) • Hacker News Board

Re: Why we ground electrical systems (2015)

#41

Post by ars » Fri, Aug 02, 2019, 7:50 PM UTC

vvillyd wrote: post #33

fsh wrote: post #23

This section is plain wrong: "The ONLY purpose for the EGC (or green wire) is to clear a ground-fault (clearing a ground-fault means tripping a breaker or blowing a fuse) in the 'oh shit moments'. It has absolutely NOTHING to do with the ground or the Earth and will work exactly as it is intended to regardless of whether it is connected to the Earth or not." If the EGC is floating, no current will flow in a ground fa…

I'm not trying to be argumentative but you are misinformed. "Floating" means that the system is not connected to ground. That is, there is no system/main bonding jumper. There is no connection to a grounding electrode conductor. This has nothing to do with the Equipment Grounding Conductor, though. I don't know what you mean by a "floating EGC". The entire purpose of the EGC is to bond all normally non-current carryi…

He's right and you are not.

If you don't bond neutral and ground at the main, it's still bound at the transformer.

> then the current will flow through the ungrounded conductor,

No, it will flow through the grounded conductor.

> back to the source (usually a transformer), across the windings, and eventually back to the breaker that controls the circuit

The flow of power is the same via ground as it is via neutral.

> This will build up enough current (usually VERY fast, like milliseconds)

There is no such thing as "build up enough current", current does not "build up".

The milliseconds has to do with built in time delays at breakers, it's not a function of the electricity.

> The Earth has nothing to do with this

The actual Earth is used as a conductor, so yes, it definitely has something to do with this.

Re: Why we ground electrical systems (2015)

#42

Post by vvillyd » Fri, Aug 02, 2019, 7:51 PM UTC

bardworx wrote: post #22

Why are there three wires in new receptacles? From my understanding, new code has you have to have a 3+ground but why is that safer? Did they just add an extra wire so you can have a hot, lead, and neutral to ground all the receptacle? (Plus the green/bare to bond the receptacle to switch/outlet) Also, for home owners, what’s the best resource to learn common sense basics of electrical work (besides reading the city/…

The three wires in any typical household circuit are your Ungrounded Conductor (hot wire), Grounded Conductor (neutral wire), and Equipment Grounding Conductor (EGC/Ground Wire). The hot and neutral are what actually makes the circuit work. The EGC/ground is a safety measure that creates a ground fault current path which enables overcurrent protective devices (like breakers and fuses) to operate.

As far as learning common electrical, I'm sure local organizations in your area will have some kind of classes. Probably local hardware stores? I don't know. I learned through trade school and on-the-job training. As an electrician, I will self-servingly tell you that you should always hire a licensed electrician.

Re: Why we ground electrical systems (2015)

#43

Post by ars » Fri, Aug 02, 2019, 7:51 PM UTC

ryanmarsh wrote: post #4

This blew my mind. So the white wire (neutral) is actually what I thought the ground was (connected to earth) and the “ground” wire (usually bare or green) is a conductor for clearing ground faults and isn’t connected to earth. Marvelous explanation.

> conductor for clearing ground faults and isn’t connected to earth.

> Marvelous explanation.

It might be Marvelous, but it's not actually true. The ground wire IS connected to the earth!

I don't want to be rude, but I think the OP should take this post down, it has a LOT of mistakes.

Re: Why we ground electrical systems (2015)

#44

Post by vvillyd » Fri, Aug 02, 2019, 7:55 PM UTC

ryanmarsh wrote: post #19

vvillyd wrote: post #12

Earlier quoted context omitted.

If you do not properly bond the ceiling fan (that is, connect the "ground" wire) then the circuit breaker will not trip if there is a fault to ground on the fan. That is, if the hot wire touches a metal part of the fan which is not supposed to be energized (say the metal housing), and the fan is not properly bonded, then there will be no ground-fault path back to the source to cause the breaker to trip. This could me…

So when installing any electrical fixtures at home I should always connect “ground” (bond the fixture) first. I’ve been connecting it last (always with the power off but accidents can happen). This could lead to an injury if someone flipped the breaker on and I accidentally touched hot to myself or the case because the breaker wouldn't trip.

Absolutely! Yes!

First, NEVER work anything hot. There is no such thing as a safe voltage to work energized. Even a simple home receptacle circuit can easily kill you (and it happens with alarming regularity).

That said, ALWAYS work something AS IF it were hot (for the exact reason you said, accidents happen). This means connecting the safety measures first. The safest order to connect wires is: ground, neutral, hot. The safest order to disconnect wires is the opposite: hot, neutral, ground.

Re: Why we ground electrical systems (2015)

#45

Post by ars » Fri, Aug 02, 2019, 7:58 PM UTC

ryanmarsh wrote: post #19

vvillyd wrote: post #12

Earlier quoted context omitted.

If you do not properly bond the ceiling fan (that is, connect the "ground" wire) then the circuit breaker will not trip if there is a fault to ground on the fan. That is, if the hot wire touches a metal part of the fan which is not supposed to be energized (say the metal housing), and the fan is not properly bonded, then there will be no ground-fault path back to the source to cause the breaker to trip. This could me…

So when installing any electrical fixtures at home I should always connect “ground” (bond the fixture) first. I’ve been connecting it last (always with the power off but accidents can happen). This could lead to an injury if someone flipped the breaker on and I accidentally touched hot to myself or the case because the breaker wouldn't trip.

> This could lead to an injury if someone flipped the breaker on and I accidentally touched hot to myself or the case because the breaker wouldn't trip.

Half right, half wrong. It would not short if it touched the metal box, and would not trip the breaker. That part is right.

However if it touched YOU not having the ground wire connected actually helps you. It means the electricity does not have as a good of a path back to the box, and you'll get a weaker shock.

With the ground wire you'll get a much higher shock, but it won't trip the breaker!! Humans have too high resistance to trip breakers, you'll just keep getting shocked.

So it's kind of a wash - with the ground, it's more likely to just short against the box and trip.

Best is just to always wire things as if they are live. Only touch the wire if you have to, always use insulated tools, even if the power is off.

Re: Why we ground electrical systems (2015)

#46

Post by temporaryvector » Fri, Aug 02, 2019, 7:59 PM UTC

vvillyd wrote: post #2

I'm actually the person who wrote this Reddit post. I'd never heard of Hacker News before, but someone messaged me on Reddit telling me this 4 year old post just surfaced over here. Let me know if you have any questions about electrical theory or installation, or anything else!

I don't have a specific question, but can you recommend a good, authoritative resource on learning to work with household electrical installations correctly, both theory and actual installation? Something like The Art of Electronics and Learning the Art of Electronics, but for general household electrical.

I do quite a bit of DIY electrical in my home, both because I enjoy tinkering and because I live in a developing country where most of the electricians you can hire is better described as "practiced amateur" rather than "professional," and I've gotten by with online resources (and the fact that my house is made from non-combustible materials) but as you point out in that post, there's a lot of conflicting or downright wrong information.

I don't want to become an actual electrician, but aside from just being interested in the topic, I'd at least want to know for sure that what I'm doing is safe and to be able to check the work of anyone I hire for obvious faults. I'm planning a solar installation in the near future, so I'd like to be well informed on how everything is supposed to work.

Re: Why we ground electrical systems (2015)

#47

Post by vvillyd » Fri, Aug 02, 2019, 8:00 PM UTC

ars wrote: post #37

vvillyd wrote: post #29

Earlier quoted context omitted.

I'm from the US, so I'll add the caveat that this is answer is based on my foreign understanding and a British electrician may be better suited to answer this. Your green wire would be what the US calls a ground wire, and what is more accurately called a Equipment Grounding Conductor (EGC). It's purpose is to bond all normally non-current carrying conductive parts of a system together to provide a ground-fault curren…

> However, without the green wire, if either the red or black shorts to something, the breaker will not open and you have an enormous potential to harm someone or burn your house down. This is not true. First of all only the red is hot, if the black shorts to something nothing will happen. Second if there is a short strong enough to "burn your house down", the breaker most definitely will open.

After researching the UK electrical system, I realize I was mistaken on one regard. I thought they used 2-ungrounded conductors, but I was mistaken. The red wire is the only ungrounded. This would be the same as the black wire in a US house. The red wire is their grounded/neutral. This would be the same as a white wire in a US house.

I am correct on the EGC, though. It works the same as the EGC in the US. If a ground fault causes a house to burn down, then the breaker will absolutely NOT open. That's how the fire starts: current flows through something it shouldn't long enough to heat it up to the point that something ignites. If the breaker opens, the fire wouldn't have started in the first place.

Re: Why we ground electrical systems (2015)

#48

Post by shreddish » Fri, Aug 02, 2019, 8:02 PM UTC

throwaway542134 wrote: post #32

shreddish wrote: post #17

Earlier quoted context omitted.

Yes water is a great way to describe electricity in a lot of ways. I'm just struggling with the "returning to where it originates". For instance the electricity didn't originate from the grounding rod it came from the transformer. Earth is providing a very low electrical potential that the electricity is "attracted" to or "falling" to in the reservoir example. Am I wrong in thinking that all electricity is flowing ba…

When you talk about "electricity" you need to distinguish between "current" and "charge carrier." Current is the amount of charge that flows through a point per second. The charge carriers are the electrically charged particles that actually move. Where current goes is a matter of what we're trying to do with a circuit, where charge carriers go is why we need ground. What a voltage does is pull or push the charge car…

Hmm okay starting to make more sense now. Do you know a good visual explanation that shows the "path" electricity takes from the transformer to your home and back out to the ground rod. Note: I fully understand in AC the electrons aren't actually moving along this path. But I guess I don't see how the circuit is ever "complete" or a circle.

Re: Why we ground electrical systems (2015)

#49

Post by NobodyNada » Fri, Aug 02, 2019, 8:04 PM UTC

shreddish wrote: post #17

throwaway542134 wrote: post #14

Earlier quoted context omitted.

I've always preferred to think of it as pumping water from the bottom of a (practically infinite) reservoir and dumping it at the top of a mountain then doing some work as it flows downhill, back to the reservoir. It provides a nice visual for why current always makes it back to ground, just like water always flow downhill. It also removes the tendency to anthropomorphize electrical current and say things like it "se…

Yes water is a great way to describe electricity in a lot of ways. I'm just struggling with the "returning to where it originates". For instance the electricity didn't originate from the grounding rod it came from the transformer. Earth is providing a very low electrical potential that the electricity is "attracted" to or "falling" to in the reservoir example. Am I wrong in thinking that all electricity is flowing ba…

Electric potential is created by a difference in electric charge between two points. Because it's a measurement between two points, it is never absolute -- "a very low electric potential" is meaningless unless you've defined what it's low relative to. A battery/electric outlet/transformer creates a potential difference across its terminals, and that's why electricity wants to flow from one terminal to the other. Usually, the terminal with the lower (more negative) potential is defined to be the 0V measurement, but this is arbitrary and out of mathematical convenience -- we could call it 1V or -1000V, and the circuit would still work the same (all that matters is the difference between the two terminals, not the absolute value of either terminal).

The neutral lines of circuits are often tied into Earth, making the voltages of the neutral line and the earth equal to one another at what we've defined to be 0V (for reasons of convenience and safety). There's no intrinsic property of Earth that gives it a low electric potential, and electricity doesn't intrinsically want to flow back into Earth.

Re: Why we ground electrical systems (2015)

#50

Post by clort » Fri, Aug 02, 2019, 8:07 PM UTC

amriksohata wrote: post #15

vvillyd wrote: post #2

I'm actually the person who wrote this Reddit post. I'd never heard of Hacker News before, but someone messaged me on Reddit telling me this 4 year old post just surfaced over here. Let me know if you have any questions about electrical theory or installation, or anything else!

So in the UK we have 3 wires, red, blue and green, the green is ground or earth, what purpose does this serve? Is it the same as ground as you call it in the US

In the UK we used to have red, black and green, but now we have brown, blue and green/yellow (I think this is the same as rest of EU). I presume this is because of colour blindness reasons as there are folk who can't distinguish red and black that well.