240 Volt GFCI Protection?

[KRG9729]

I don't understand how a 3 wire GFCI circuit is supposed to work. I know on a 120 volt circuit it monitors the current between the hot and neutral and shunt trips when there is slight imbalance. Any help would be appreciated,

 

[zog]

Are you maybe confusing a GFI with a GFCI?

 

[speedypetey]

A 240v GFI breaker works exactly the same way, only it monitors both 120v and 240v at the same time.
You can have an imbalance in the two legs of the breaker because the neutral will carry it. The GFI knows this.

 

[zog]

A 240v GFI breaker works exactly the same way, only it monitors both 120v and 240v at the same time.
You can have an imbalance in the two legs of the breaker because the neutral will carry it. The GFI knows this.

I think you are talking about a GFCI, not a GFI.

 

[speedypetey]

I think you are talking about a GFCI, not a GFI.

What is your point???

If you are being anal about it, YES, you are correct. The proper term is GFCI. GFI is easier to write and generally accepted. I classify it along with "neutral" instead of grounded conductor and "ground" instead of grounding conductor.

 

[hillbilly1]

You don't even have to have a 120 volt load for it to work, it senses current flow anywhere it travels outside of the hots or neutral. Think of it as a current transformer that has both hots and neutral run through it, as long as no current is going around the outside the CT, everythings fine, but when the leakage reachs a predetermined point it trips. Ground fault switchgears work on the same principal, just that the set point is a lot higher.

 

[zog]

What is your point???

If you are being anal about it, YES, you are correct. The proper term is GFCI. GFI is easier to write and generally accepted. I classify it along with "neutral" instead of grounded conductor and "ground" instead of grounding conductor.

"Apples" is also easier to write (1 charlater shorter) than "Oranges". A GFI is not a GFCI and they should not be confused with one another,I dont know who it is "generally accepted by" to interchange these two very different devices with completely differently purposes. I have seen OSHA accident investigations from fatalaties at industrial plants that believed they didnt need GFCI's on thier receptacles because thier breakers had GFI's. Guess thier plant elecricians didnt think there was a difference either.

 

[electricmanscott]

" Guess thier plant elecricians didnt think there was a difference either.

I don't know what you are getting at but if you are going to nit pick......:grin:

 

[Minuteman]

"Apples" is also easier to write (1 charlater shorter) than "Oranges".

I'm just saying. :grin:

 

[Rampage_Rick]

I don't understand how a 3 wire GFCI circuit is supposed to work. I know on a 120 volt circuit it monitors the current between the hot and neutral and shunt trips when there is slight imbalance. Any help would be appreciated,

The easiest way to visualize the operation of a GFCI is to picture a clamp-on ammeter. If you clamp around the hot and neutral on a 120v circuit, you'll get a reading of zero (assuming no ground fault ) This is because the current going each way is equal and cancels the other out.

The same is true for a 240V circuit. If you were to clamp around both hots and the neutral, you'd see zero current. If you're pulling 10A on one leg, 6A on the other leg, and 4A on the neutral, the net current through the ammeter is still zero.

The instant that the reading is NOT zero, there must be an imbalance somewhere, implying a ground fault.