GFCI operation question

the way a GFCI functions, would it trip
if a bad connection were made to it ?
(if say, a terminal with the hot or
neutral wasn't screwed down tight &
a plugged in load drew current causing
the terminal to warm up - would the
GFCI trip ?)
Reply to
Methos
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The load's current use is sensed by the GFCI whether wired dubiously as in the example you imposed.
The problem child is when the grounding and neutral are swapped.
Arcing, as implied by your example, needs an AFI circuit for detection.
Reply to
Jonny
I don't think so. Why would the resistance of a bad connection be any different from the resistance of a light bulb.
I wouldn't assume there will be arcing just because a connection isn't tight enough. So I wouldn't assume that even an arc fault circuit breaker would be tripped by a loose connection. Am I right or wrong?
Reply to
mm
Methos
A GFIC is made to trip on sudden line voltage changes. A slow warm up would not trip the built in breaker. This very problem cause a house fire that burned a third of my parents house to the ground. Two wires in some old Romex touched and caused a slow short but it was not enough to trip the breakers. Therefore, it warmed up long enough to catch fire.
GFIC's are a nice safety feature but it certainly doesn't catch all problems
Reply to
LightsAREon
There's all kinds of "bad connections". If the bad connection resulted in a difference of 5 mA or more between the current in the neutral versus the current in the hot wire, the GFCI would trip. The example you gave would not cause the GFCI to trip.
Ed
Reply to
ehsjr
As others have mentioned, a GFCI would probably not trip. They sense current differences, and usually have current overload sensing in them also. But a bad connection causing the terminal to warm up would not trip it unless it got very hot, and even then the results are indeterminate.
Reply to
Zootal
So far there has been a lot of misinformation in replies to this thread.
Only the smoke will indicate a simple HOT connection. If there is any arcing a AFCI should detect the fault and disconnect.
Quote
"The ?AFCI? is an arc fault circuit interrupter. AFCIs are newly-developed electrical devices designed to protect against fires caused by arcing faults in the home electrical wiring."
****
A GFCI will only protect from differences in the current flowing in the two conductors beyond the GFCI. It will cutoff the current when a very small current difference, 5 or 30 ma., is detected and should do it quick enough to save a person from electrocution.
Neither device is intended to protect from voltage spikes and neither device can detect a simple hot connection.
A hot connection alone will not csause a difference in current between the 2 legs of the circuit, only a ground fault can cause that and a GFCI should detect that.
Reply to
John G
thanks everyone for the responses.
the powerpoint link was very informative.
if i understood it correctly, any current differential
if one terminal has contact resistance (loose), wouldn't the current flow on that leg be reduced by the amount of resistance ? and therefore trip the GFCI ? (since it would see less on one leg, vs the other - or am I misinterpreting, since a hot/load/neutral circuit is basically in series, and current is only depended on how much the device draws?)
Reply to
Methos
Both wires are part of the same series circuit and the current will be the same whileever there is no other path (ground).
Current in = current out.
The resistance of the contact will be part of the impedance (along with the real load) that determines the magnitude of the current.
Reply to
John G
Let me say what I said another way. GFCI outlets and circuit breakers measure if there is a difference between the amount of current going throught the hot wire and though the neutral wire. If they are the same, the gfci sees no problem. Having a loose connection does not mean that will happen. Using an appliance that shorts to your body and from there to some other path than the neutral wire *would* cause it to trip.
OTOH, if you took two all-metal screwdrivers, one in each hand, and stuck one into each of the slots in an outlett, even a GFCI outlet, you could burn your heart to a fine grey ash, and the breaker would not trip. Because the same amount of current was going through the two conductors.
Reply to
mm
I agree with others that a GFCi wouldn't trip on a loose connection.
A loose connection can produce enough heat to start a fire without arcing (a "glowing" connection). Late stages in failure are likely to arc.
AFCIs sense "parallel" arcs - from hot-to-neutral (a "fault", the F in AFCI). Starting in 2008 the NEC requires them to also detect "series" arcs, as in a loose connection. As far as I know, no current AFCIs detect series arcs, so none would detect a loose connection.
GFCIs trip on a difference in current between the hot and neutral, not line voltage changes. They are primarily for electrocution protection.
The "slow short" you describe, an arc that trips a breaker slowly, if at all, is exacty what AFCIs are designed to protect against. A more likely cause is probably an abused extension cord.
AFCIs also include 30mA ground fault protection (GFCIs have 5mA protection). The idea is, I think, that if a ground wire is adjacent, a hot-to-neutral arc is likely to also become hot-to-ground.
bud--
Reply to
Bud--
Methos It sounds like bud has the right answer. I hadn't heard about the upcoming AFIC's but will certainly pass the info on to everyone at my office (I'm a construction administrator for a large architectural firm). Thanks bud for the education. LightsAREon
Reply to
LightsAREon
I don't believe it's "upcoming". I think that all AFCI's currently have 30ma ground fault protection for equipment.
Reply to
PPS
They call it Ground-Fault Protection of Equipment when it is at the 30ma level. BTW get used to AFCIs. They will be on all 120v 15 and 20a circuits in a dwelling in 2008 if the code goes as drafted. Comments are still open until October.
Reply to
gfretwell
Yea - it is to detect the arc, not protect people. AFCIs can have a 5 mA ground fault trip and be used as both AFCI and GFCI. It would require 2 test buttons. Probably would see them if the code change below goes into effect.
To PPS - I presume "upcoming" is the requirement to detect "series" arcs starting 2008, not 30mA ground fault trip.
Considering the new AFCIs aren't on the market (or are they recently out?), and it is only about 1.5 years for field experience until they are required in 2008, it seems like requiring the new AFCIs in all 15/20A dwelling circuits is not a great idea (whatever the wisdom of requiring the current AFCIs is). Bet there are plenty of comments on that code change.
An interesting piece on AFCIs, including why normal breakers are inadequate for arcs and arcs that shouldn't trip them is at:
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bud--
Reply to
Bud--

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