Just curious how a 240V or even a 208V 1-ph GFCI operates, I know the 120v measures the current on the hot and the neutral and when there is a 5milliamp differences it opens the circuit (correct me if I am wrong) but how does a 240V GFCI work? The neutral connected to the brkr? Then is the sum of the two hot legs compared to the neutral current? How does that work with motors or losses across loads? Just curious. Thanks in advance.:-?
240V GFCI Operation
- Thread starter Mike01
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Sierrasparky
Senior Member
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- USA
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- Electrician ,contractor
From what I have seen is that the current is measured on each leg and ground and imbalance from the hot must flow on the Neutral. Otherwise it is flowing to ground causing a trip at the current level set. It just cannot vanish into thin air.
LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
Quick description: Whether 2- or 3-wire, all circuit conductors (including neutral) pass through a single torroid core (do-nut), which also has a small coil wrapped around one side.
Just as in metallic conduit, as long as all current in any one conductor is equalled (opposed) by current in another conductor or conductors, no voltage is developed in the small coil.
If any current through one conductor is not equalled by opposing current, a proportionate voltage is developed in the small coil, and when it reaches a set point, it trips the device.
The need to include all currents, including that of the neutral, is why the circuit neutral, if there is one, must land on the GFCI, and it's also why MWBC's require multi-pole GFCI's.
Added: Also, GFCI neutrals must land on the system neutral bus even if the load circuit has no neutral conductor
Just as in metallic conduit, as long as all current in any one conductor is equalled (opposed) by current in another conductor or conductors, no voltage is developed in the small coil.
If any current through one conductor is not equalled by opposing current, a proportionate voltage is developed in the small coil, and when it reaches a set point, it trips the device.
The need to include all currents, including that of the neutral, is why the circuit neutral, if there is one, must land on the GFCI, and it's also why MWBC's require multi-pole GFCI's.
Added: Also, GFCI neutrals must land on the system neutral bus even if the load circuit has no neutral conductor
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Sierrasparky
Senior Member
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- USA
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- Electrician ,contractor
nicely done.
Mr Fine
Mr Fine
hardworkingstiff
Senior Member
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Sierrasparky said:
Yea, he's pretty sharp (actually, very sharp).
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
"Aww, you guys!"
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