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Lxnxjxhx
Guest
A "GFI" is a differential ammeter giving a pass/fail indication within 10 seconds for resistive or reactive leakage currents above 4 mA.
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zog
Senior Member
- Location
- Charlotte, NC
Sounds like you are lloking for a def of a GFCI, not a GFI. There is no GFI in the NEC, you will find a GFCI in the NEC.
A GFI is a type of GFP that is required on service entrances >150V and 1000A or more. GFP is for minimizing damage to equipment from excessive groud currents and is not designed or inteded for protection of personel from electric shocks.
GFCI's operate with a small current transformer that surrounds both the line and neutral wires. The secondary winding is connected to a sensitive electronic detector, which can trigger a circuit breaker or contactor in series with the 120-volt line. Most GFCI's trip at an unbalance of as little as 4-6 mA. Under normal conditions, the line current in the line conductor is equal to the current in the neutral, and so the net current flowing through the current transformer is zero. Consequently, no flux is produced in the core, the induced voltage is zero, and the circuit breaker or contactor remains shut. A GFCI has nothing to do with the current on the grounding conductor, they are for personel protection.
A GFI is a type of GFP that is required on service entrances >150V and 1000A or more. GFP is for minimizing damage to equipment from excessive groud currents and is not designed or inteded for protection of personel from electric shocks.
GFCI's operate with a small current transformer that surrounds both the line and neutral wires. The secondary winding is connected to a sensitive electronic detector, which can trigger a circuit breaker or contactor in series with the 120-volt line. Most GFCI's trip at an unbalance of as little as 4-6 mA. Under normal conditions, the line current in the line conductor is equal to the current in the neutral, and so the net current flowing through the current transformer is zero. Consequently, no flux is produced in the core, the induced voltage is zero, and the circuit breaker or contactor remains shut. A GFCI has nothing to do with the current on the grounding conductor, they are for personel protection.
- Location
- Massachusetts
langjahr@comcast.net said:
No I don't think that was.
But if you look in Article 100 you will find the NEC definition of Ground-Fault Circuit Interrupter. :smile:
The FPN right after the definition is also worth a read.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Well, first it's not an "ammeter," since it does not display the amount of measured current. Secondly, it is not a "pass/fail" situation; it trips on high current. Finally, it cannot distinguish resistive current from reactive current. So I don't think I would agree with your definition. Sorry.
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Lxnxjxhx
Guest
Back to the drawing board!
cloudymacleod
Senior Member
well the gfci does trips out at 4 to 6 milliamps but i know that doesn't answer your ?.
76nemo
Senior Member
- Location
- Ogdensburg, NY
langjahr@comcast.net said:
Would you like to be more specific so we can answer your question, or would you prefer to find it alone? That's one of the biggest +'s to the forum, we are all entitled to questions:wink:
zog
Senior Member
- Location
- Charlotte, NC
Here is a practical one:
A device that compares the "Goesin" current to the "Goesout" current and trips if they are not equal.
A device that compares the "Goesin" current to the "Goesout" current and trips if they are not equal.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
GFI = Girl Friend Interrupter; a device which, when installed on your phone, makes random static noises that increase with intensity and frequency the longer she talks to you, thereby allowing you to gracefully cut the conversation short without ruining your chances for a "happy ending" later on.
Side note; there is no such thing as a "Wife Interrupter" because that would be impossible. Besides, you'll have to listen to her anyway when you get home, so it wouldn't do any good.
Side note; there is no such thing as a "Wife Interrupter" because that would be impossible. Besides, you'll have to listen to her anyway when you get home, so it wouldn't do any good.
iaov
Senior Member
- Location
- Rhinelander WI
Sounds like a salesmans description. If it took a GFCI 10 seconds to react however it would not save very many lives!:smile:langjahr@comcast.net said:
mdshunk
Senior Member
- Location
- Right here.
It's so simple. It's all ball-bearings nowadays:
A ground interrupter GFCI receptacle comprising the combination of a receptacle having hot neutral and ground connectors for receiving blades of a mating plug first and second pairs of terminals for connection to AC source and load wires said first pair of terminals being specifically designated for connection to hot and neutral wires from said source and said second pah of terminals being designated for connection to hot and neutral wires leading to a load device first circuit means for connecting said hot and neutral connectors of said receptacle to said second pair of terminals second circuit means connecting said first pah of terminals to said receptacle connectors said second circuit means including contact sets openable to disconnect said first pair of terminals from said receptacle connectors means for opening said contact sets current sensing means responsive to a net current flow greater than a predetermined amount through said second circuit means for actuating said means for opening said contact sets and manually operable supervisory circuit means connected between said hot connector of said receptacle and ground without being connected to said neutral connector for selectively actuating said means for opening said contact sets to test operation of said means for opening without giving a false indication of proper installation of said GFCI receptacle.
A ground interrupter GFCI receptacle comprising the combination of a receptacle having hot neutral and ground connectors for receiving blades of a mating plug first and second pairs of terminals for connection to AC source and load wires said first pair of terminals being specifically designated for connection to hot and neutral wires from said source and said second pah of terminals being designated for connection to hot and neutral wires leading to a load device first circuit means for connecting said hot and neutral connectors of said receptacle to said second pair of terminals second circuit means connecting said first pah of terminals to said receptacle connectors said second circuit means including contact sets openable to disconnect said first pair of terminals from said receptacle connectors means for opening said contact sets current sensing means responsive to a net current flow greater than a predetermined amount through said second circuit means for actuating said means for opening said contact sets and manually operable supervisory circuit means connected between said hot connector of said receptacle and ground without being connected to said neutral connector for selectively actuating said means for opening said contact sets to test operation of said means for opening without giving a false indication of proper installation of said GFCI receptacle.
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Lxnxjxhx
Guest
It's so simple
It's so simple
I used to work in the Patent Office, and that text looks like a patent claim!
It's so simple
I used to work in the Patent Office, and that text looks like a patent claim!
- Location
- Illinois
- Occupation
- retired electrician
Actually the UL standard permits up to ~5.6 seconds for the GFCI to trip with a 6 mA ground fault.
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Lxnxjxhx
Guest
UL standard permits up to ~5.6 seconds
UL standard permits up to ~5.6 seconds
Yes, (20/6)^1.43 = 5.6 seconds, and 4 mA gives 10 seconds. If you spec one value you are also spec'ing the other value, if this formula is valid.
I thought this formula calculated the center values, with an unspecified tolerance around these center values, but maybe it calculates the maximum time that the user is exposed to the shock. I don't have a copy of the UL spec.
They could have made a GFI with a comparator that trips immediately above a minimum value, say 4 mA, but they might have had a good reason to do it this way instead. Maybe to warn the user with a small, "safe" shock that there is a leakage problem. . .?
I remember back in the 70's, when I was still an IEEE member, that they had an article about shocking 150 pound dogs, and some people, I suppose to collect data as to what humans could safely tolerate, as a prelude to making a GFI.
If you plot the equation above, you will probably get what 95% or 99% or 99.9% of people can safely tolerate as to current x time, from these studies.
100% certainty = infinite cost.
So a person is kind of like a fuse, except a fuse responds to I^2, and this formula shows that the sensitivity of people to I is proportional to the 1.43 power.
Apparently the GFI specs were better thought out than the AFCI specs.
UL standard permits up to ~5.6 seconds
Yes, (20/6)^1.43 = 5.6 seconds, and 4 mA gives 10 seconds. If you spec one value you are also spec'ing the other value, if this formula is valid.
I thought this formula calculated the center values, with an unspecified tolerance around these center values, but maybe it calculates the maximum time that the user is exposed to the shock. I don't have a copy of the UL spec.
They could have made a GFI with a comparator that trips immediately above a minimum value, say 4 mA, but they might have had a good reason to do it this way instead. Maybe to warn the user with a small, "safe" shock that there is a leakage problem. . .?
I remember back in the 70's, when I was still an IEEE member, that they had an article about shocking 150 pound dogs, and some people, I suppose to collect data as to what humans could safely tolerate, as a prelude to making a GFI.
If you plot the equation above, you will probably get what 95% or 99% or 99.9% of people can safely tolerate as to current x time, from these studies.
100% certainty = infinite cost.
So a person is kind of like a fuse, except a fuse responds to I^2, and this formula shows that the sensitivity of people to I is proportional to the 1.43 power.
Apparently the GFI specs were better thought out than the AFCI specs.
zog
Senior Member
- Location
- Charlotte, NC
I think you are getting confused between your post here and in the Engingeering group. Are you asking about a GFI or a GFCI?
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Lxnxjxhx
Guest
a GFI or a GFCI?
a GFI or a GFCI?
This one's about GFI trip specs for the protection of people. I'm just now working out the differences between a GFI and the other things.
a GFI or a GFCI?
This one's about GFI trip specs for the protection of people. I'm just now working out the differences between a GFI and the other things.
zog
Senior Member
- Location
- Charlotte, NC
GFI's dont protect people, they are for minimzing equipment damage from ground faults.
A GFCI is for protecting people and I gave a desription of how it works earlier. You are confusing the 2 very different devices, as many people do.
A GFCI is for protecting people and I gave a desription of how it works earlier. You are confusing the 2 very different devices, as many people do.
brian john
Senior Member
- Location
- Leesburg, VA
I will use this for sure......
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