Can you explain how a 2 pole, 240 volt, 60 amp gfci breaker works on a three wire system? It has a neutral tail coming off it but no place to land a ground/neutral wire. If this breaker (square D) will work on a 3 wire system, then why will it not work on a 4wire 120/240 v system? I know code doesn't allow it, I'm just wondering how do they work differently from oneanother?
240 volt gfci breaker
- Thread starter perlin68
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I believe the GFCI breaker you are referring to is intended for 240/208V, 2-wire loads only, even though it is not specified. As to why the tail exists with no load neutral terminal, only Sq D can answer!perlin68 said:
- Location
- Massachusetts
Smart $ said:
I have been told that the neutral is used to run the electronics in the breaker.
This way the same power supply can be used for 1 or 2 pole breakers.
BUT...I have no proof of that.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
iwire said:
Actually the neutral wire is there to provide the TEST function of the breaker.
jim dungar said:
Ground Fault works through the induced magnetic field of the currents passing through a coil. As long as the current going to the load exactly matches the current returning from the load you are okay.
A ground fault bleeds current on the load side that causes a mismatch in the currents. To test the current you have to have a way to unbalance the load currents. As Jim stated, a small tap to a neutral that does not go through the GFCI coil would do just that.
perlin68 said:
I guess to the question of the OP.
The neutral is not actually being used in powering the end device. The end device is using the 240VAC phase power. Therefore no current is being passed through the ground/neutral wire. Only the hots are passing through the GFCI coil. There should be no neutral current from the device.
Yes strictly speaking it would work with a 4 wire system as neither the ground nor neutral would pass through the coil. For testing the neutral and not the ground would go on the tail. But UL always wins.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
pfalcon said:
The breaker does not care if it is connected to a 4 wire system, unless by chance the test circuit is connected to a leg of 208V to "neutral" (can be found in 240/120 3-phase 4-wire).
I believe the breaker is rated for a circuit (not a system) that does not exceed 120V to ground.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
I disagree. If there is any neutral current at all (okay, >5ma), the GFCI would trip.pfalcon said:
Any neutral current is current that passes through one hot wire that is not identical in the other hot wire.
The breaker might not care, but if there is any neutral current, see above.jim dungar said:
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
LarryFine said:
Larry, if it is a 240 or 208V 2-wire circuit fed from a 4-wire system, where is the circuit neutral coming from? And we definitely want the GFCI to trip if the sum of the current through it is >5mA.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I took this line . . .jim dungar said:
. . . to mean that the load has a neutral conductor, and there would be an attempt to land it directly on the neutral bus.pfalcon said:
Of course, as long as the load is line-to-line only, and there will be no neutral conductor, I am in agreement with you.
Part of the key is remembering which breaker you are talking about.
And Larry and I agree here. It also makes this a dedicated run because additional loads that might use the neutral would trip the breaker, which is the point I think Jim was making.
On the other hand, I spent a little time wandering through the SquareD website. None of the wiring diagrams were for 2-wire loads. This makes more sense because a washer/dryer would use 120V controls which will create a neutral current. Double check the wiring diagram for the GFCI. What did you mean by "a neutral tail".
Smart $ said:
LarryFine said:
And Larry and I agree here. It also makes this a dedicated run because additional loads that might use the neutral would trip the breaker, which is the point I think Jim was making.
On the other hand, I spent a little time wandering through the SquareD website. None of the wiring diagrams were for 2-wire loads. This makes more sense because a washer/dryer would use 120V controls which will create a neutral current. Double check the wiring diagram for the GFCI. What did you mean by "a neutral tail".
perlin68 said:
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Summarizing: most, but not all, 2-pole 60A GFCI breakers are intended to feed 2-wire circuits and as such do not have provisions for a load neutral connection. However, they have a line side neutral pig-tail (120V max) for their electronics.
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