EGC question

[Rayne]

So a hot conductor touches the metal casing on an receptacle and if there’s no egc and we come along touch the outlet and complete the path back to the source Equals shock , ok I’ve been reading about how equipment grounding conductors prevent electrocution because the high current from that same situation travels back on the equipment grounding conductor which then would trip the breaker causing no harm to us. How does the egc trip the breaker, it’s not hooked up to the breaker, what am I missing here

 

[Coppersmith]

The hot conductor touches the metal casing (junction box) on a receptacle and THERE IS AN EGC (which is connected to the box). The circuit is completed and is a dead short so lots of amps flow. The breaker trips because the amperage flowing exceeds the breaker's rating.

If the hot conductor were to touch the metal junction box very lightly it's possible it could create a high resistance short which would not trip the breaker but would probably create a lot of smoke and light from an arc. The arc would eventually die off as the metal burned away but could start again if somebody vibrated the receptacle by plugging something in it. The user may get a shock if they touch the screw or a metal cover since the electrons follow ALL PATHS to ground, not just the shortest one or the ground wire.

 

[LarryFine]

How does the egc trip the breaker, it’s not hooked up to the breaker, what am I missing here

The EGC system is connected to the service neutral in the enclosure where the main breaker is, whether it's in the breaker panel or a separate main breaker ahead of the panel. So, a hot-to-EGC short has the same effect as a hot-to-neutral short.

 

[Rayne]

The EGC system is connected to the service neutral in the enclosure where the main breaker is, whether it's in the breaker panel or a separate main breaker ahead of the panel. So, a hot-to-EGC short has the same effect as a hot-to-neutral short.

Oh okay so when a short happens there is a high amount of current flowing through the hot conductor through egc completing the circuit and those high amps would be more than what the breaker allows causing it to trip , when there is no egc And theirs a short we could complete that circuit

 

[g3guy]

ok I’ve been reading about how equipment grounding conductors prevent electrocution because the high current from that same situation travels back on the equipment grounding conductor which then would trip the breaker causing no harm to us

Unless that's GFCI protected, you're toast!

 

[Carultch]

Oh okay so when a short happens there is a high amount of current flowing through the hot conductor through egc completing the circuit and those high amps would be more than what the breaker allows causing it to trip , when there is no egc And theirs a short we could complete that circuit

If there is no EGC, and there is a short to any piece of metal that should normally not be energized, that piece of metal will be come energized when the ungrounded conductor contacts it. It will carry a voltage difference between it and the actual ground. If a human body touches this energized piece of metal, as well as a non-energized conductive material, that human body will carry the current and get shocked. This is what we want to avoid.

Connecting the EGC to any device that has a metal housing, means that there is a path for return current to flow back to the panelboard, and trip the breaker, thus turning the circuit OFF, and de-energizing the metal housing.

Any non-energized piece of metal or conductive material that has a chance of becoming electrically energized, needs to be bonded to the equipment grounding system. The EGC system itself gets bonded to the actual ground via the grounding electrode at the service disconnect, as well as to the neutral of the electrical service. The building steel and the foundation are also bonded to the EGC system, so throughout the building, non-energized metal and concrete remains non-energized.

If you had plastic housing instead of metal housing on a device, plastic would not get energized when the ungrounded wire faults to it. This is why you often see two prong plugs on devices that have plastic housing.

 

[LarryFine]

If you had plastic housing instead of metal housing on a device, plastic would not get energized when the ungrounded wire faults to it. This is why you often see two prong plugs on devices that have plastic housing.

As well as an additional insulation level, such as at least one plastic gear in a drill's gear train.