Gfi question: If you put a current into the neutral side, without current coming from the "hot side".....

Question

of the receptacle- what happens?

Answer 1

The current has to go somewhere, if there is a current at all.  The question,is, if not 'out' the hot side, where is it going?

My best guess is that a GFI watches to see if hot current is equal to neutral current using a transformer of some sort.  If any noticeable difference exists, I'd expect it to trip.  

Why not test it with a laboratory power supply?

Answer 2

The GFI reads any difference in the 'phase'' and 'neutral'

lines. That's how it recognizes the low 'leakage' currents

it's designed to protect you from.

If you did feed current from a different line to the

'neutral', it should trip out.

Answer 3

The GFI will trip.  It is basically a differential relay that looks for a 5 mA current imbalance -- then trips.

Sometimes an outlet is wired "backwards" and the neutral side is actually the the hot leg.

Answer 4

The GFI will trip.

The GFI has a transformer that measures the difference between the currents in the hot and the neutral leads. And if the difference is higher than about 4 ma, then it pops the breaker.

The reason is that if you drop a hair dryer into the tub, the classic case, with the hair dryer drawing say 8 amps, you will get some current from the hot wire to ground, ie, current that does not flow back into the neutral. For example, the current out of the hot lead may be 8.010 amps, and the return current into the neutral would be 8.000 amps, and the GFI senses that difference and trips the breaker.

So if you inject a current into the neutral side (probably referenced to ground) then the breaker will pop, if that current is higher than about 5ma.

IF: that is, it will trip if the current you inject is in phase with the voltage from hot lead. In phase or 180 out of phase. The GFI transformer has to see an inphase voltage of the same frequency.

.

Answer 5

Just hook it up the way it says.............so if you get whacked with your hand in the pool or sink.........it might save your life......it's like the old story about the two patients in room 222 one went in to have a vasectomy and the other to have his lower legs removed........the nurse got the charts confused and guess what........the wrong guy got his legs cut off........what would you do?.......He said he was mad and wanted to sue.............but his lawyer told him he didn't have a leg to stand on........lol....do it right