...
Could you possibly explain more about the first paragraph of your response? Are you possibly referring to an ungrounded system? In a grounded system (as this one is) one conductor (negative in this case) is connected to earth ground at one point only. As previously stated, this is an off-grid, stand-alone installation. The PV conductors from the panels go to a charge controller inside the house, with an inverter running off a 24v battery bank that is kept charged by the charge controller. You explained about the first ground fault on one conductor and a possible second ground-fault on the second conductor?.. in this particular installation, wouldn?t a single ground-fault (on the positive conductor) be problematic, possibly causing arcing that could lead to a fire?
Thanks again for your input! Nick
What I said about first and second faults applies equally to both grounded and ungrounded systems, as far as the intended purpose of GFDI goes. (Technically with solar it is
Ground
Fault
Detection and
Interruption, meaning interruption of the operation of the system. This is distinguished from other Ground Fault Protection devices which typically de-energize the faulted conductor(s). GFDI in solar does not de-energize the faulted PV conductor(s).)
To address your question in your final sentence, in a grounded system the GFDI device
ungrounds the grounded conductor when it trips, thus interrupting the arcing that could lead to a fire if there is only one fault. Typically the grounded conductor is connected to ground through a fuse and if the fault current is enough to blow the fuse then the connection is broken.
Fused methods of GFDI on grounded systems are less sensitive than methods for ungrounded systems, and have led to at least
one major diaster. A fault on an ungrounded conductor is usually enough to blow the GFDI fuse since the entire short circuit current can possibly take that path. One smaller systems the resistance of the fault only needs to be less than the inverter, and on systems with combiners a fault in a source circuit can blow the source circuit fuse. However, a fault on a grounded conductor needs to be roughly equal in resistance to the actual circuit conductor, which requires a stronger fault to blow the fuse. In either case really small ground faults can be missed by the typical 1A fuse for residential systems.
By contrast, the methods used by ungrounded systems are very sensitive, even too sensitive in my opinion. (The inverter tests the insulation of the conductors before startup, and monitors the current electronically during operation to make sure it remains balanced.) In one case I had to replace wiring on a system where the fault being detected would have been passing around a third of a milliamp.
Pretty much all grid-tied inverters being sold these days are ungrounded for better safety. Off-grid systems with batteries haven't really caught up yet.