Ground fault path from negative wire in negative grounded DC system

[philly]

What is the current path if the negative wire in a DC PV system is grounded. I know that if the positive wire is grounded the ground current travels along the equipment ground conductor through the bonding jumper (ususally in inverter with GFD device) and then returns to the PV module

What happens if the negative wire comes in accident contact with the ground? Is there any current flow? What path would the current take?

I would not think there is any current flow since the negative and ground are at the same potential?

 

[SG-1]

There will be current flow between the deliberate ground & the unintentional ground. Some current will leave the negative conductor at the point of the fault & flow on the frame, establishing a parallel path over part of the system.

 

[philly]

There will be current flow between the deliberate ground & the unintentional ground. Some current will leave the negative conductor at the point of the fault & flow on the frame, establishing a parallel path over part of the system.

How would there be currnent flow if the negative wire and the ground were bonded together and therefore at the same potential?

Would it be because there would still be a small resistance between where the negative wire fault occured to ground and the negative terminal of the PV source circuit? Since there is this small resistance there would be a small votlage drop present and therefore would have a small current? The current would not be nearly as high as if the positive wire was shorted to ground? Would this be enough current to pickup the ground fault detection device?

 

[cadpoint]

I would not think there is any current flow since the negative and ground are at the same potential?

Delete ......

 

[SG-1]

As a model think about an AC system with metalic raceways. The grounded conductor is bonded at the source. The raceway is bonded & at ground potential.
50 ft down a raceway the the grounded conductor comes into accidental contact with the raceway. The current on the grounded conductor will return to the source using all paths available. The raceway ( or a frame) becomes a parallel path.

No more current would flow after the fault than before, only a portion of the current would leave the grounded conductor for the raceway. The resistance of the fault will help determine the amount. If the ungrounded conductor comes into contact with the raceway the current will go wild until an OCPD interrupts it.

The negative & ground are only at the exact same potential at the bond. The resistance per foot of the grounded conductor causes a voltage drop as the distance increases provided current is flowing. On an AC system there is a difference of potential between the grounded conductor & the EGC. Measure between the neutral & ground at a recptacle. There would be a simular difference of potential in a DC system also.

If I had a conductor 100ft long with a resistance of .01 ohm. A current equal to 100 amps is flowing through the conductor. If you were to measure the voltage from one end of the conductor to the other end it would be V=IxR or V= 100 x .01= 1 volt. If one end is grounded it has no effect on the voltage reading, because the conductor itself is the resistor.