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

Re: Why we ground electrical systems (2015)

#81

Post by chrisdhoover » Fri, Aug 02, 2019, 11:45 PM UTC

ars wrote: post #78

vvillyd wrote: post #42

Earlier quoted context omitted.

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 c…

> 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. This is NOT TRUE!! You've said it so many times in this thread, and it's just not true. A lot of people are tying to correct your mistakes, but you're not fixing them. Please do so, you are misleading a lot of people.

Perhaps you could explain it correctly?

Re: Why we ground electrical systems (2015)

#82

Post by chrisdhoover » Sat, Aug 03, 2019, 12:14 AM UTC

alexhutcheson wrote: post #30

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.

They are both connected to earth at the same point. The big difference is that "neutral" has current flowing through it during normal operation, but "ground" only has current flowing through it in a fault condition.

Right because the hot/black is connected to the neutral/white through the load completing a circuit so current flows. The “ground”/green is only connected to the chassis so no current flows in normal operation.

Re: Why we ground electrical systems (2015)

#83

Post by chrisdhoover » Sat, Aug 03, 2019, 12:19 AM UTC

vvillyd wrote: post #13

shreddish wrote: post #10

Earlier quoted context omitted.

From my understanding, if the hot wire (black) were to come in contact with a piece of metal on the fan it would build up electrical charge and or allow for current to pass through the piece of the fan. Then if you were on a ladder fixing the fan and touched that piece of metal you would become a path for electricity to pass through to a lower potential.

That's exactly correct. You would get shocked if you touched the fan.

The way you bond is codified too. The source feed is wire-nutted with a pigtail connected to the box, and to the ground of the device in parallel. If the bonding was daisy chained it could be interrupted when servicing or changing.

Re: Why we ground electrical systems (2015)

#84

Post by dreamcompiler » Sat, Aug 03, 2019, 12:41 AM UTC

shreddish wrote: post #16

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…

Technically, would it only shock you if your body provided a path to "ground" or lower potential? For example if you were wearing insulted boots and touched the energized piece of metal you would not feel a shock, correct?

Correct. But if you touched the energized piece of metal with one hand and accidentally touched a grounded conductor with the other hand, you'd be dead. This is why in the rare circumstances when I have to work on an energized high-voltage circuit (don't do this!) I observe the "keep one hand in your pocket" rule.

Re: Why we ground electrical systems (2015)

#85

Post by chendragon » Sat, Aug 03, 2019, 12:42 AM UTC

Unsimplified wrote: post #60

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!

For a machine, is it generally a good idea to distribute a common power bus voltage like 48VDC to independent modules (embedded computers, servo controllers) for them to stepdown inside the application module (12vdc, 24vdc) or should the power be stepped down early at the distributor module? What are the advanced tradeoffs?

Generally the higher the voltage you distribute, the lower the current in the wires, allowing you to use thinner wire and reducing I^2R losses.

With this said, having multiple point of load converters may have impacts on efficiency and will add to the cost of the system.

Re: Why we ground electrical systems (2015)

#86

Post by mindslight » Sat, Aug 03, 2019, 12:42 AM UTC

watersb wrote: post #66

I have been studying Grounding vs Bonding these past few weeks, great timing to see this HN discussion. Some training videos for pro electricians and US National Electric Code compliance helped me. https://youtu.be/qNZC782SzAQ Basically, bond everything together if it can carry a charge. Ground that bond at only one place in an electrical service. More than one "ground" sets up a situation where a potential differenc…

Watching this video (myth #3) brings up a bit of a semantic peeve. And that peeve begins with how the NEC narrowly defines the term "grounding" as only applying to the electrical system itself. Then electricians apply that narrow definition to every use of the term, acting like someone is wrong because they say they're "grounding" something by hooking up it up to an EGC.

But don't worry, they'll teach you this special term "bonding" that refers to the latter. Except it doesn't. I already used a synonym of "bonding" - "hooking up". You "bond" the black wire to the gold terminal on a receptacle by tightening the screw.

> Basically, bond everything together if it can carry a charge

It is perfectly fine to say that you are grounding those things together. Connecting something to an EGC is indeed "grounding it" - just not in NEC land which is focused on getting the EGC grounded. If you say "this washing machine needs to be better grounded", that doesn't mean it needs an immediate connection to earth, but is rather talking about its path to earth via the building's electrical system.

Re: Why we ground electrical systems (2015)

#87

Post by dreamcompiler » Sat, Aug 03, 2019, 12:47 AM 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.

In industrial and commercial settings, there are "Lockout/Tagout" rules. These prevent -- either through policy or physical means -- somebody from accidentally flipping a breaker back on when maintenance is occurring.

Re: Why we ground electrical systems (2015)

#88

Post by wtallis » Sat, Aug 03, 2019, 12:57 AM UTC

chrisdhoover wrote: post #81

ars wrote: post #78

Earlier quoted context omitted.

> 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. This is NOT TRUE!! You've said it so many times in this thread, and it's just not true. A lot of people are tying to correct your mistakes, but you're not fixing them. Please do so, you are misleading a lot of people.

Perhaps you could explain it correctly?

You can trip a breaker without the ground wire being involved. The ground wire does help with one failure case, but that's not the only way that your circuit breakers/fuses protect you.

Re: Why we ground electrical systems (2015)

#89

Post by wrycoder » Sat, Aug 03, 2019, 1:48 AM UTC

jessaustin wrote: post #57

ars wrote: post #43

Earlier quoted context omitted.

> 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.

TFA is a bit more abstract than you realize, and perhaps that abstraction could mislead the unwary. It is technically correct, but makes a distinction you've missed. If a gremlin cuts the (green) wire between my breaker box and my ground rod, the system is no longer "grounded to Earth", so it wouldn't handle lightning strikes well. However, the "EGC" in every house circuit is still bonded to neutral at the box, so br…

In the USA, there's no green wire between the service panel and the ground rod. The green wires end at the ground bus in the panel, which is bonded to the panel case. A heavy, bare copper wire leads from the ground bus to the ground rod.

The neutral bus is either bonded to the case with a green grounding screw or is integral with the ground bus.

Re: Why we ground electrical systems (2015)

#90

Post by wrycoder » Sat, Aug 03, 2019, 1:56 AM 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…

> EGC (which is bonded to the box), back to the source (usually a transformer)

EGC is bonded to the panel enclosure at the ground bus. The neutral bus is also bonded to the enclosure with a ground screw. So, the EGC is directly connected to the neutral bus and a fault between hot and a bonded enclosure is routed via the EGC to neutral, tripping the breaker.