GFCI receptacle

[New EE]

Could someone please tell me if the following statement is accurate.


Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be installed in a 2 wire circuit, the GFCI does not create a safety ground. In fact, shorting between the Hot and Ground terminals in the GFCI receptacle will do absolutely nothing if the GFCI is not connected to a grounded circuit (at least for a typical GFCI receptacle). It will trip only if a fault occurs such that current flows to a true ground. If the original circuit did not have a safety ground, the third terminal is not connected. What this means is that an appliance with a 3 prong plug can develop a short between Hot and the (supposedly) grounded case but the GFCI will not trip until someone touches the case and an earth ground (e.g. water pipe, ground from some other circuit, etc.) at the same time.

Note that even though this is acceptable by the NEC, I do not consider it desirable. A person?s safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. Therefore, if at all possible, it?s best to provide a proper code compliant ground connection to all receptacles by connecting to a proper grounding conductor.

 

[texie]

Could someone please tell me if the following statement is accurate.


Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be installed in a 2 wire circuit, the GFCI does not create a safety ground. In fact, shorting between the Hot and Ground terminals in the GFCI receptacle will do absolutely nothing if the GFCI is not connected to a grounded circuit (at least for a typical GFCI receptacle). It will trip only if a fault occurs such that current flows to a true ground. If the original circuit did not have a safety ground, the third terminal is not connected. What this means is that an appliance with a 3 prong plug can develop a short between Hot and the (supposedly) grounded case but the GFCI will not trip until someone touches the case and an earth ground (e.g. water pipe, ground from some other circuit, etc.) at the same time.

Note that even though this is acceptable by the NEC, I do not consider it desirable. A person?s safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. Therefore, if at all possible, it?s best to provide a proper code compliant ground connection to all receptacles by connecting to a proper grounding conductor.

All valid points. I think that the NEC folks feel that this is better than nothing in an old house with wiring that does not have an EGC. It should also be noted that there are some cases where you absolutely need the EGC for various reasons.

 

[don_resqcapt19]

Could someone please tell me if the following statement is accurate.


Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be installed in a 2 wire circuit, the GFCI does not create a safety ground. In fact, shorting between the Hot and Ground terminals in the GFCI receptacle will do absolutely nothing if the GFCI is not connected to a grounded circuit (at least for a typical GFCI receptacle). It will trip only if a fault occurs such that current flows to a true ground. If the original circuit did not have a safety ground, the third terminal is not connected. What this means is that an appliance with a 3 prong plug can develop a short between Hot and the (supposedly) grounded case but the GFCI will not trip until someone touches the case and an earth ground (e.g. water pipe, ground from some other circuit, etc.) at the same time.

Note that even though this is acceptable by the NEC, I do not consider it desirable. A person?s safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. Therefore, if at all possible, it?s best to provide a proper code compliant ground connection to all receptacles by connecting to a proper grounding conductor.

How is any of that any different from the case of a ground fault on an appliance with a two wire cord? I have a coffee pot and a toaster within reach right now and both have two wire cords and exposed metal parts.

That being said, I agree with you. For the most part an EGC connection will prevent the shock and GFCI protection will only limit the duration of the shock.

 

[iwire]

Note that even though this is acceptable by the NEC, I do not consider it desirable. A person?s safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. Therefore, if at all possible, it?s best to provide a proper code compliant ground connection to all receptacles by connecting to a proper grounding conductor.

I also agree with you.

But if the choice is a GFCI or nothing I think the GFCI is a good compromise.

The NEC cannot force homeowners to rewire the branch circuit just because an old two wire receptacle wears out.

 

[George Stolz]

The NEC cannot force homeowners to rewire the branch circuit just because an old two wire receptacle wears out.

Shh - they might think it's a challenge and do it anyway!

 

[Ohms law]

I also agree with you.

But if the choice is a GFCI or nothing I think the GFCI is a good compromise.

The NEC cannot force homeowners to rewire the branch circuit just because an old two wire receptacle wears out.

Except when replacing 2-prong because a receptacle broke. I have not seen any 2-prong tamper resistant, so therefore wouldn't you have to replace with 3-prong by default? If you have no EG then you would have to GFCI protect the branch circuit, correct?

 

[kwired]

Except when replacing 2-prong because a receptacle broke. I have not seen any 2-prong tamper resistant, so therefore wouldn't you have to replace with 3-prong by default? If you have no EG then you would have to GFCI protect the branch circuit, correct?

You do not have to GFCI protect the branch circuit, though it is an option, you only need to GFCI protect any grounding type receptacles that are not supplied with an equipment grounding conductor.

And it is only an exception for existing wiring that doesn't include an equipment grounding conductor, you can not use the exception for a new installation or even for an extension of an existing circuit and omit the equipment grounding conductor.

 

[fmtjfw]

Could someone please tell me if the following statement is accurate.


Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be installed in a 2 wire circuit, the GFCI does not create a safety ground. In fact, shorting between the Hot and Ground terminals in the GFCI receptacle will do absolutely nothing if the GFCI is not connected to a grounded circuit (at least for a typical GFCI receptacle). It will trip only if a fault occurs such that current flows to a true ground. If the original circuit did not have a safety ground, the third terminal is not connected. What this means is that an appliance with a 3 prong plug can develop a short between Hot and the (supposedly) grounded case but the GFCI will not trip until someone touches the case and an earth ground (e.g. water pipe, ground from some other circuit, etc.) at the same time.

Note that even though this is acceptable by the NEC, I do not consider it desirable. A person?s safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. Therefore, if at all possible, it?s best to provide a proper code compliant ground connection to all receptacles by connecting to a proper grounding conductor.

A GFCI know nothing about GROUND. It looks for a current differential between HOT and NEUTRAL. If that difference exceeds 6mA, it trips. If a person touches the HOT side of the circuit and causes 6mA or more of current to flow somewhere (other than the NEUTRAL) it trips very quickly and is considered very protective of the person.

Fuses and circuit breakers don't directly protect a person from shock. They only protect indirectly, by opening a circuit that has a considerable overcurrent, at least 3 orders of magnitude above currents dangerous to a person.

 

[kwired]

A GFCI know nothing about GROUND. It looks for a current differential between HOT and NEUTRAL. If that difference exceeds 6mA, it trips. If a person touches the HOT side of the circuit and causes 6mA or more of current to flow somewhere (other than the NEUTRAL) it trips very quickly and is considered very protective of the person.

Though not as likely to happen, if a person touched the neutral side and enough current happened to flow outside the protected portion of the circuit it would also trip.

 

[iwire]

Except when replacing 2-prong because a receptacle broke. I have not seen any 2-prong tamper resistant, so therefore wouldn't you have to replace with 3-prong by default? If you have no EG then you would have to GFCI protect the branch circuit, correct?

You really lost me here.

 

[don_resqcapt19]

... I have not seen any 2-prong tamper resistant, so therefore wouldn't you have to replace with 3-prong by default? ...

No. See 406.12 Exception(4).

 

[iwire]

A GFCI know nothing about GROUND. It looks for a current differential between HOT and NEUTRAL. If that difference exceeds 6mA, it trips. If a person touches the HOT side of the circuit and causes 6mA or more of current to flow somewhere (other than the NEUTRAL) it trips very quickly and is considered very protective of the person.

True but at the same time the only place that current can flow is towards what that poster called 'true ground' because we only use GFCIs on grounded voltage systems.

It could be the dirt of the earth, a plumbing pipe etc.

 

[JDBrown]

Well, since you asked...

Could someone please tell me if the following statement is accurate.


Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be installed in a 2 wire circuit, the GFCI does not create a safety ground. In fact, shorting between the Hot and Ground terminals in the GFCI receptacle will do absolutely nothing if the GFCI is not connected to a grounded circuit <-- The term you're looking for here is "Equipment Grounding Conductor" (EGC). A 2-wire residential circuit with no EGC is still a grounded circuit, because the neutral wire is grounded at the service. (at least for a typical GFCI receptacle). It will trip only if a fault occurs such that current flows to a true ground. <-- This isn't quite accurate. The GFCI will trip if the current flowing on the hot and neutral wires is unbalanced by more than 6mA. That current can be on ANY alternate path, not just an EGC. This is why GFCIs can cause problems with MWBCs, for example, because you can end up with current on the neutral that doesn't match the current on the hot. If the original circuit did not have a safety ground, the third terminal is not connected. What this means is that an appliance with a 3 prong plug can develop a short between Hot and the (supposedly) grounded case but the GFCI will not trip until someone touches the case and an earth ground (e.g. water pipe, ground from some other circuit, etc.) at the same time. <-- This is all true.

Note that even though this is acceptable by the NEC, I do not consider it desirable. <-- While it's not the ideal, it's only allowed for existing installations anyway, and the idea is to protect life without making people gut their homes. Are you really going to tell Grandma that she has to rip out all her drywall and rewire her whole house to make sure she's got an EGC at each receptacle? Sure it'd be nice if the EGC was there, but often it's just not practical to add one in an existing installation. A person?s safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. <-- I don't know about that. You don't often hear about GFCIs failing in the "power on" position. They're actually pretty darn reliable. Anyway, their purpose is totally different from the purpose of a fuse or breaker. The GFCI is designed to protect life, while the fuse or circuit breaker is designed to prevent fires and/or protect equipment. It's happened on more than one occasion that a breaker opened in plenty of time to prevent a fire, but someone was still electrocuted. Therefore, if at all possible, it?s best to provide a proper code compliant ground connection to all receptacles by connecting to a proper grounding conductor. <-- True. I like that you included "if at all possible." It really is the best solution; it just isn't always feasible.

 

[kwired]

True but at the same time the only place that current can flow is towards what that poster called 'true ground' because we only use GFCIs on grounded voltage systems.

It could be the dirt of the earth, a plumbing pipe etc.

Current will flow toward any other difference in potential whether it be grounded, or not. Could be to the other ungrounded conductor (240 volts) and it would still be current flowing outside the sensing coil - GFCI still trips, or could have neutral returning from another circuit through the GFCI - again current flowing outside the sensing coil will trip the GFCI, unless it doesn't reach the 4-6 mA threshold.

 

[iwire]

Current will flow toward any other difference in potential whether it be grounded, or not.

:slaphead:

Yeah, big thanks for that.

Could be to the other ungrounded conductor (240 volts) and it would still be current flowing outside the sensing coil -

So what you are saying is if someone grabs one hot from the load side of a GFCI and then, grabs another hot of a different phase not protected by the first GFCI that the GFCI would trip?

Yes, I concede that is true and you see it happening all the time.

 

[kwired]

:slaphead:

Yeah, big thanks for that.




So what you are saying is if someone grabs one hot from the load side of a GFCI and then, grabs another hot of a different phase not protected by the first GFCI that the GFCI would trip?

Yes, I concede that is true and you see it happening all the time.

Well it probably doesn't happen all that often, but many still do not really understand how a GFCI works. All it cares about is that the current flowing in on any protected conductor comes back on another proted conductor (within 4-6 mA of leakage being tolerable) is about as basic of a description of how it works as you can get. It doesn't care what is hot, what is grounded, or even what the voltage is, - now the control circuit will care what voltage is but sensing coil doesn't. You do anything imaginable to create more than 4-6 mA of unbalance in the sensing coil and have acceptable voltage to the control component, and it is tripping no matter what any other conditions are.

There are still many people that come here asking about GFCI operation, whether grounding is needed for them to work, and other questions of that nature. The basic concept is simple enough - maybe there should be questions related to this on J-man licensing exams.