GFCI and an Open Ground
Given: A 120 VAC GFCI supplying power to a 30 AMP RV. The RV has one problem, the 3rd Prong Ground wire at the 30 AMP plug is not making connection. (The RV chassis is floating because there are no ot...
Forum Discussion
road-runner wrote:The downstream neutral-ground fault detection does not use the current imbalance detector, but rather a different mechanism. An example can bee seen here: http://www.onsemi.com/pub/Collateral/FAN4147-D.pdf
When I looked at how they do this, I discovered that the GFCI simply induces current into the wires which in turn trips the very same current imbalance detector. So while no external current is flowing, there is some inside the device. Regardless, an RV without a ground path will not trip from current imbalance or shorted neutral & ground.
Diagram on page 2, description starts near the bottom left of page 5. Older designs did use 120 Hz. signal injection, but still used a separate transformer for detection.
But the description describes a "grounded neutral" which goes back to the question of how can you have a "grounded neutral" when there is no ground connection at all to the trailer. Current does not flow into an open ended wire. And an ungrounded frame is effectively an open ended conductor.
