If a Classic 200 or Classic 250 is used in a system with multiple charge controllers and the other charge controllers are legacy devices, it seems like we can get into trouble with ground fault protection. NEC 690.35(C) says the GFP "disconnects all conductors or causes the inverter or charge controller connected to the faulted circuit to automatically cease supplying power to output circuits."
For installations with multiple Classic charge controllers or even Classic and X-X X- MPPT60 charge controllers that have built-in GFP protection, the GFP should only be activated for the Classic connected to the PV array with the highest voltage. Any ground fault will shut down all of the charge controllers. But most importantly, a ground fault in the high voltage PV array is opened by a device rated for the appropriate voltage.
The problem isn't so easy for legacy systems using an external GFP breaker. If the GFP in the Classic 200 were activated in addition to the external GFP, the GFP system would still work, it would be less sensitive; but there are worse problems. If the Classic's GFP is faster than the external breaker-based GFP, it will always be the first one to open. That leaves the external GFP possibly exposed to a ground fault in the high-voltage array - a condition for which it isn't designed and thus a code violation. If the external GFP is abandoned then any ground fault will trip the GFP protection in the Classic, but the legacy charge controllers remain connected. While the fault may have cleared, the system is clearly in violation of 690.35(C).
On first though it seems like a solution would be an option to slow the Classic's GFP function down so that the external breaker-based GFP opens first and disconnects the legacy PV array. This would not be opening a high voltage fault; the fault isn't cleared until the Classic's GFP opens. Unfortunately, there is no way to know ahead of time how long a breaker-based GFP will take to operate. If the fault current is small it can take a long time. I observed over five seconds in one system.
A second solution would be to replace all of the existing charge controllers. If you think that doesn't sound like a waste, try to sell that to your customer with legacy MPPT charge controllers.
Another solution is to use an external high-voltage GFP, anyone know of a 300-volt GFP that can handle three PV arrays? In panel mount format? Remember it's a legacy system.
Quote from: Kent0 on January 31, 2011, 03:07:51 PMIf the GFP in the Classic 200 were activated in addition to the external GFP, the GFP system would still work, it would be less sensitive; but there are worse problems. If the Classic's GFP is faster than the external breaker-based GFP, it will always be the first one to open. That leaves the external GFP possibly exposed to a ground fault in the high-voltage array - a condition for which it isn't designed and thus a code violation. If the external GFP is abandoned then any ground fault will trip the GFP protection in the Classic, but the legacy charge controllers remain connected. While the fault may have cleared, the system is clearly in violation of 690.35(C).
If an external GFP is installed in the usual way in the BOS box, how about just pulling the GFP jumper in the Classic an let the one GFP do the interrupting?
Since the Classic looks at voltage between negative and ground, then, if there is any fault voltage left over between ground and negative, the Classics will see this and shut off with a GF error.
Quote from: Kent0 on January 31, 2011, 03:07:51 PM
On first though it seems like a solution would be an option to slow the Classic's GFP function down so that the external breaker-based GFP opens first and disconnects the legacy PV array. This would not be opening a high voltage fault; the fault isn't cleared until the Classic's GFP opens. Unfortunately, there is no way to know ahead of time how long a breaker-based GFP will take to operate. If the fault current is small it can take a long time. I observed over five seconds in one system.
This is certainly possible too (delay)... Simple matter of programming (SMOP) and we can talk about that one too.
Quote from: Kent0 on January 31, 2011, 03:07:51 PM
A second solution would be to replace all of the existing charge controllers. If you think that doesn't sound like a waste, try to sell that to your customer with legacy MPPT charge controllers.
Another solution is to use an external high-voltage GFP, anyone know of a 300-volt GFP that can handle three PV arrays? In panel mount format? Remember it's a legacy system.
I'll let Robin, Ryan and others (and myself) chew on all of these a bit.
Thanks Kent,
boB
boB,
The problem with the external GFP is that the 1/2-A breaker needs to be rated for the maximum Voc of the highest voltage array. The Classic can shut down the new PV array when the negative-ground bond is interrupted, that saves the need for another set of contacts on the external GFP. But the external GFP breaker has to successfully interrupt the fault first. Bolt the PV positive to ground, open the GFP, and what voltage appears across the GFP's 1/2-A breaker contacts - the entire array voltage.
So when we add a Classic 200 to an existing system with an external GFP, it'll need a new GFP rated for 250 or 300 volts.
I have another solution. Get the other manufacturers' charge controllers to shut down on loss of negative-ground bond. Not much chance of that.
I think a legacy system GFP compatibility section needs to be included in the Classic manual.