GFCI (when will they trip?)

[Accurate1]

#1. If an electric drill with a metal casing is powered by a GFCI receptacle will the GFCI still trip if the ground wire pin in the cord is cut?


#2. If an electric drill with a metal casing is powered by a GFCI receptacle will the GFCI still trip if the ground wire pin in the cord is cut AND polarity is reversed?

 

[Buck Parrish]

GFCI Does not use the grounding conductor. It only uses the hot (black) and the neutral (white).
So
#1 no
#2 maybe

 

[480sparky]

...........#2. If an electric drill with a metal casing is powered by a GFCI receptacle will the GFCI still trip if the ground wire pin in the cord is cut AND polarity is reversed?

Polarity of the cord or the polarity of the GFI?

 

[LarryFine]

Welcome to the forum!

#1. No.

#2. No. (presuming you mean the load)

 

[quogueelectric]

I will go with a double no also.

 

[iwire]

Polarity of the cord or the polarity of the GFI?

It would not mater, the GFCI will still operate.

 

[realolman]

I think the OP is wondering whether a ground fault on the drill, presumably through the operator, will cause the GFCI to operate if the ground pin on the drill is missing.

It would if the operator were grounded well enough.

That's the reason for the ground pin and the EGC.... so that wires are a much better path for faults than you are.

So long as the neutral and the hot both carry the same amount of current, the GFCI is happy. However it happens that the neutral and hot have different amounts of current on them, the GFCI is not happy, and trips.

 

[dbuckley]

#1. If an electric drill with a metal casing is powered by a GFCI receptacle will the GFCI still trip if the ground wire pin in the cord is cut?

If a ground fault develops in the drill the GFCI will trip irrespective of the presence or absence of the ground wire, as long as (a) there is a path to ground from the drill body, normally provided by the person holding the drill, and (b) there is enough of a potential difference to cause a few milliamps of current to flow. So hot direct to body will almost certainly trip the GFCI, whereas N to body probably wont if the ground wire is cut, but a N to G direct connection will usually trip a GFCI.

As further proof of this, imagine that drill with its ground wire connected with its three prong plug being plugged into a GFCI outlet in an auld house with no ground wiring in it. The GFCI still looks after you.

#2. If an electric drill with a metal casing is powered by a GFCI receptacle will the GFCI still trip if the ground wire pin in the cord is cut AND polarity is reversed?

Same answer as above.

GFCIs are as near as dammit black magic and will save your life, even if you try hard to thwart them.

 

[mcclary's electrical]

In situation 1 if the drill has a fault internally and the operator is grounded then, yes, it would still trip. If the cord is faulty, knicked and grounded, yes it would trip.

#2, if the polarity of the cord is reversed, it would not matter. it would still trip. If the polarity of the GFI is wrong, it most likely will not even come on at all.

 

[iwire]

If the polarity of the GFI is wrong, it most likely will not even come on at all.

Unless something has changed I do not believe that to be true.

The newer GFCIs protect against wiring the line into the load side terminals but I do not think any have 'polarity protection'

 

[mcclary's electrical]

You're right, I just tested your theory on a Cooper and it will work both ways. I guessed I just assumed. I had never tried it reverse polarity. Interesting.

 

[iwire]

I just tested your theory on a Cooper

Your the man, thanks for the extra effort.

 

[LarryFine]

#1 revisited: The purpose of the EGC is to have a lower resistance than you to ground, for the purpose of tripping a standard breaker.

The GFCI is of little use with a fault from a hot wire to an EGC-bonded surface.


#2 revisited: The only effect of reversing polarity on a GFCI-protected circuit is it changes which wire has to fault to the user for the shock to occur, and the GFCI to operate.

 

[winnie]

Based upon the a description of how 'smartlock' GFCIs function, it would be _possible_ for a GFCI to detect reverse polarity and prevent operation.

As I understand it, these GFCIs perform a self test when the 'reset' button is pressed. It is plausible that the GFCI could measure the 'L-G' and the 'L-N' voltages, and based upon these measurements it could fail the test with reverse polarity.

I don't believe that any GFCIs implement this sort of function, because this would make them unreliable if the ground were not present...but this sort of function is at least possible.

Hmm. In some environments, you are required to ensure that the ground is present. Perhaps there is a market for GFCIs that won't reset without proper polarity and correct grounding....

-Jon

 

[iwire]

Presently GFCI receptacles are expected to be able to work on two wire circuits. I do not know of any way a GFCI could tell the polarity of a simple two wire circuit.

 

[mcclary's electrical]

#1 revisited: The purpose of the EGC is to have a lower resistance than you to ground, for the purpose of tripping a standard breaker.

The GFCI is of little use with a fault from a hot wire to an EGC-bonded surface.


#2 revisited: The only effect of reversing polarity on a GFCI-protected circuit is it changes which wire has to fault to the user for the shock to occur, and the GFCI to operate.

I disagree with this statement, The ground fault looks for the exact same current to "comeback" as has left, therefor IMO a fault could occur in either wire to ground and trip the gfi. The GFI should see neutral current "NOT RETURNING" if the neutral is grounded downstream. A fault in either wire will trip the GFI, or at least in theory.

 

[don_resqcapt19]

I disagree with this statement, The ground fault looks for the exact same current to "comeback" as has left, therefor IMO a fault could occur in either wire to ground and trip the gfi. The GFI should see neutral current "NOT RETURNING" if the neutral is grounded downstream. A fault in either wire will trip the GFI, or at least in theory.

While it will see the missing current,no matter which conductor has the ground fault, it is unlikely that there will be enough voltage to ground on the grounded conductor to drive 5 mA through the person. A grounded conductor fault to an EGC or other conductive grounded object will likely cause the GFCI to trip.

 

[mcclary's electrical]

While it will see the missing current,no matter which conductor has the ground fault, it is unlikely that there will be enough voltage to ground on the grounded conductor to drive 5 mA through the person. A grounded conductor fault to an EGC or other conductive grounded object will likely cause the GFCI to trip.

In most cases I would agree, but in this case we were talking about a metel drill, IMO, a metal drill, ungrounded, with a grounded conductor fault internal, held tightly in the palms of a sweating person could reach 5mA easily. IMO. it's only a guess.

 

[hurk27]

In most cases I would agree, but in this case we were talking about a metel drill, IMO, a metal drill, ungrounded, with a grounded conductor fault internal, held tightly in the palms of a sweating person could reach 5mA easily. IMO. it's only a guess.

oh the guy on the metal ladder in the middle of the swimming pool:roll:

 

[don_resqcapt19]

In most cases I would agree, but in this case we were talking about a metel drill, IMO, a metal drill, ungrounded, with a grounded conductor fault internal, held tightly in the palms of a sweating person could reach 5mA easily. IMO. it's only a guess.

I really doubt it. The only voltage available to drive the current would be the voltage drop on the grounded conductor between the system or main bonding jumper and the drill. This would normally only be a few volts and very unlikely to be able to drive 5 mA.