GFP vs ARC fault protection?

[n00bs0lar]

Would some one please explain the difference between the ground fault protection and the arc fault protection? I'm having a hard time visualizing what type of events would trip one and not the other. Would someone please give an example of what type of events would trip the GFP and what type of event would trip the ARC Fault protection in the classic? Thanks!

[Kent0]

Arcs and sparks will occur when a dc circuit is opened under load. This could result from a broken wire, a connector that is pulled loose, or from the operation of a switch. Midnite has a video online showing the Classic's arc fault protection working when a knife switch is slowly opened. This is a series arc and it is extinguished by stopping the current from flowing through the circuit. Stop the current and the arc stops.

A ground fault is when the PV positive wire touches something that is grounded, such as the PV module frame. This can happen because a wire is rubbed against the frame while being moved by the wind, or if someone pulls on the PV array wiring causing the insulation to be cut. A ground fault is a parallel fault, the current (or some of it) doesn't follow the normal path. There may or may not be any arcs associated with a ground fault. Often there will be an arc but not always. If all of the wiring is as it is supposed to be, the parallel path is a path through the system bond, that's the point where PV- is connected to ground. The ground fault protector opens, stops the current, and also stops any arcs associated with the ground fault. If the wiring isn't right, the ground fault protector may not operate at all. If the initial arc is too large and hot the ground fault protector may operate but won't stop the arc from spreading and creating alternate ground paths.

The arc fault protector may sense the arc associated with a ground fault. It may open the circuit. But it won't extinguish an arcing ground fault. At present the NEC only requires the arc fault protection to extinguish a series fault. It is a lot more complicated problem for it to know how to extinguish either series or parallel faults.

[vtmaps]

The arc fault protector may sense the arc associated with a ground fault. It may open the circuit. But it won't extinguish an arcing ground fault. At present the NEC only requires the arc fault protection to extinguish a series fault.

I think I saw an announcement of an arc-fault combiner box.  Would it extinguish an arcing ground fault?  Would it also extinguish a series fault, making the arc fault protector in the CC redundant?
--vtMaps

[Halfcrazy]

The Classic has Series Arc fault protection in it. We are working on a line of combiner boxes as well for systems that need Arc Fault. Our combiners will do Series and Parallel Arc Fault protection. Parallel will be an add on option.

My opinion is GF does not really do much for Fire safety and actually can present a hazard to life and limb. We feel Arc Fault on the roof is the safest bet as it will disconnect as much of the system as feasible and handle the AF in the rest accordingly.

Ryan

[Westbranch]

Ryan, don't you mean "at the array" rather than "Arc Fault on the roof"   ?

[Halfcrazy]

Good catch sorry about that

Ryan

[n00bs0lar]

Arcs and sparks will occur when a dc circuit is opened under load. This could result from a broken wire, a connector that is pulled loose, or from the operation of a switch. Midnite has a video online showing the Classic's arc fault protection working when a knife switch is slowly opened. This is a series arc and it is extinguished by stopping the current from flowing through the circuit. Stop the current and the arc stops.

A ground fault is when the PV positive wire touches something that is grounded, such as the PV module frame. This can happen because a wire is rubbed against the frame while being moved by the wind, or if someone pulls on the PV array wiring causing the insulation to be cut. A ground fault is a parallel fault, the current (or some of it) doesn't follow the normal path. There may or may not be any arcs associated with a ground fault. Often there will be an arc but not always. If all of the wiring is as it is supposed to be, the parallel path is a path through the system bond, that's the point where PV- is connected to ground. The ground fault protector opens, stops the current, and also stops any arcs associated with the ground fault. If the wiring isn't right, the ground fault protector may not operate at all. If the initial arc is too large and hot the ground fault protector may operate but won't stop the arc from spreading and creating alternate ground paths.

The arc fault protector may sense the arc associated with a ground fault. It may open the circuit. But it won't extinguish an arcing ground fault. At present the NEC only requires the arc fault protection to extinguish a series fault. It is a lot more complicated problem for it to know how to extinguish either series or parallel faults.

This helped tremendously, thanks!

[vtmaps]

We are working on a line of combiner boxes as well for systems that need Arc Fault. Our combiners will do Series and Parallel Arc Fault protection.

If I obtain one of your forthcoming arc fault combiners, doesn't that mean that the arc fault protection in the Classic is redundant and not needed?  --vtMaps

[boB]

We are working on a line of combiner boxes as well for systems that need Arc Fault. Our combiners will do Series and Parallel Arc Fault protection.

If I obtain one of your forthcoming arc fault combiners, doesn't that mean that the arc fault protection in the Classic is redundant and not needed?  --vtMaps

Yes, I think you are correct there !

boB

[Robin]

The arc fault combiners are intended for high voltage grid tie systems. These combiners are not cheap! For systems that use the Classic, you will not need the arc fault combiners. You are allowed to have combiners that do not have internal disconnects. Since circuit breakers can be turned off and on under load, you do not need the more expensive fused disconnecting combiners. That said, we do have a disconnecting combiner for you breaker guys. IT is the MNPV6 Disco and the MNPV6-250 Disco. Pretty cool mechanisn that just moves the handles of the breakers up and down.