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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 blow

by fsh 7y ago

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 fault and the breaker never trips.

jhayward 7y ago
If the EGC is floating, it's not an EGC. EGC is tied back to Neutral at the distribution point. Its sole purpose is to carry fault current.
- fsh 7y ago
  And the neutral is tied to (earth) ground. Otherwise all metal devices would shock you if you touched something earth referenced, such as a radiator, at the same time. Edit to clarify: In principle, only the voltage difference between Live and Neutral matters for running a device. So theoretically one could construct a building supply where Neutral is not at earth potential. However, EGC has to be at earth potential, otherwise there would be a voltage between any metal electronic device and earthed objects, such as radiators or your feet standing in a puddle. This means that in practice both Neutral and EGC are always physically connected to the earth in some way and have to be for the system to work properly.
vvillyd 7y ago
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 carrying conductive parts together to provide a ground-fault current path back to the source of the circuit. If the EGC is not connected to some non-current carrying conductive part, then it is not installed correctly, is against code, and is a safety hazard. If the EGC is bonded to everything properly and there is a fault (say an ungrounded wire touches a metal box), then the current will flow through the ungrounded conductor, through the metal box, through the EGC (which is bonded to the box), back to the source (usually a transformer), across the windings, and eventually back to the breaker that controls the circuit. This will build up enough current (usually VERY fast, like milliseconds) and the breaker will open. The Earth has nothing to do with this.
- ars 7y ago
  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.
  - jessaustin 7y ago
    If you don't bond neutral and ground at the main, it's still bound at the transformer. That would be a pretty good trick. The transformer is outside my house on a pole. Two wires run to it, the hot and the neutral. The "ground" doesn't leave the house. (Other wiring schemes exist, but this is standard USA residential.) [EDIT: brainfart, see helpful correction below. still no "ground" at the pole...]
    - jhayward 7y ago
      > Two wires run to it, the hot and the neutral Standard US residential is 240V split phase, with two hot and one neutral conductor from the transformer. So three wires, minimum. Unless you have a very old feed.
      - jessaustin 7y ago
        Ah, yes, well spotted. That was an oversimplification. Two hots, one neutral, zero "grounds".
    - ars 7y ago
      > still no "ground" at the pole... Yes there is. The neutral is bonded to ground, via an actual metal pole in the ground. In your house is the same thing: The neutral (and the ground) and attached to a metal pole in the ground. And the earth itself completes the circuit.
jotm 7y ago
I'm confused by that as well. The green wire needs to touch the earth, whether by being bonded to neutral at the distribution point or simply by touching the earth somewhere, even through a concrete wall. I've seen houses where the earth wiring is completely independent and terminated in a metal rod buried outside. Seemed to be up to local code, breakers worked as they should.
- vvillyd 7y ago
  So I think you should define what you mean by "green wire". The NEC allows EGCs, GECs, MBJs, and SBJs to all use green wire. They all serve different purposes, and only the GEC is connected to the Earth. Whether or not the GEC is present the EGC and MBJ/SBJ is what allows breakers to work properly. The MBJ/SBJ is what bonds the neutral. This doesn't have anything to do with the Earth. This bonding has to be done anywhere between the origination of the circuit and the first overcurrent protective device. The GEC is what connects to the Earth. This is used to stabilize voltage and to eliminate a difference in potential between metal parts during a high frequency event (like a nearby lightning strike or a transformer blowing up). This has nothing to do with the operation of breakers.

by fsh 7y ago

jhayward 7y ago

If the EGC is floating, it's not an EGC. EGC is tied back to Neutral at the distribution point. Its sole purpose is to carry fault current.

fsh 7y ago
And the neutral is tied to (earth) ground. Otherwise all metal devices would shock you if you touched something earth referenced, such as a radiator, at the same time. Edit to clarify: In principle, only the voltage difference between Live and Neutral matters for running a device. So theoretically one could construct a building supply where Neutral is not at earth potential. However, EGC has to be at earth potential, otherwise there would be a voltage between any metal electronic device and earthed objects, such as radiators or your feet standing in a puddle. This means that in practice both Neutral and EGC are always physically connected to the earth in some way and have to be for the system to work properly.

vvillyd 7y ago

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 carrying conductive parts together to provide a ground-fault current path back to the source of the circuit. If the EGC is not connected to some non-current carrying conductive part, then it is not installed correctly, is against code, and is a safety hazard. If the EGC is bonded to everything properly and there is a fault (say an ungrounded wire touches a metal box), then the current will flow through the ungrounded conductor, through the metal box, through the EGC (which is bonded to the box), back to the source (usually a transformer), across the windings, and eventually back to the breaker that controls the circuit. This will build up enough current (usually VERY fast, like milliseconds) and the breaker will open. The Earth has nothing to do with this.

ars 7y ago
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.
- jessaustin 7y ago
  If you don't bond neutral and ground at the main, it's still bound at the transformer. That would be a pretty good trick. The transformer is outside my house on a pole. Two wires run to it, the hot and the neutral. The "ground" doesn't leave the house. (Other wiring schemes exist, but this is standard USA residential.) [EDIT: brainfart, see helpful correction below. still no "ground" at the pole...]
  - jhayward 7y ago
    > Two wires run to it, the hot and the neutral Standard US residential is 240V split phase, with two hot and one neutral conductor from the transformer. So three wires, minimum. Unless you have a very old feed.
    - jessaustin 7y ago
      Ah, yes, well spotted. That was an oversimplification. Two hots, one neutral, zero "grounds".
  - ars 7y ago
    > still no "ground" at the pole... Yes there is. The neutral is bonded to ground, via an actual metal pole in the ground. In your house is the same thing: The neutral (and the ground) and attached to a metal pole in the ground. And the earth itself completes the circuit.

jotm 7y ago

I'm confused by that as well. The green wire needs to touch the earth, whether by being bonded to neutral at the distribution point or simply by touching the earth somewhere, even through a concrete wall. I've seen houses where the earth wiring is completely independent and terminated in a metal rod buried outside. Seemed to be up to local code, breakers worked as they should.

vvillyd 7y ago
So I think you should define what you mean by "green wire". The NEC allows EGCs, GECs, MBJs, and SBJs to all use green wire. They all serve different purposes, and only the GEC is connected to the Earth. Whether or not the GEC is present the EGC and MBJ/SBJ is what allows breakers to work properly. The MBJ/SBJ is what bonds the neutral. This doesn't have anything to do with the Earth. This bonding has to be done anywhere between the origination of the circuit and the first overcurrent protective device. The GEC is what connects to the Earth. This is used to stabilize voltage and to eliminate a difference in potential between metal parts during a high frequency event (like a nearby lightning strike or a transformer blowing up). This has nothing to do with the operation of breakers.