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690.11 dc Arc Fault Protection and 690.12 Rapid Shutdown of PV Systems


Q:

I've been reading recently about 2014 requirements for arc fault protection (690.11) and rapid shutdown (690.12). Both seem relevant for sales personnel, particularly the rapid shutdown requirements because of the potential for added equipment. Any good resources folks can recommend in this area?
 
A:
 
You are right, it is important for sales people to understand 690.11 dc arc fault protection and 690.12 rapid shutdown requirements.
 
690.11 became into play in the 2011 NEC for series arc faults. PV systems have to have dc arc fault protection and you would have a hard time finding an inverter that didn’t have dc arc fault protection.

A series arc fault is what happens if a PV connector started to come apart and there was a gap. The gap would start arcing and could start a fire if it didn’t burn itself out first.
 
If you have a large central inverter, then the inverter would have trouble detecting the arc with so many strings to keep track of and you would have to have the dc arc fault protection at the combiner.
 
690.12 Rapid Shutdown of PV Systems on or in Buildings came into play in the 2014 NEC and has been controversial. Many solar installers do not like having more rules that cost money and time. In defense of 690.12, firefighters are reluctant to climb on burning buildings that have electricity hidden in the walls when the power to the building is turned off. We hear them say “let it burn”. This is not good and Rapid Shutdown requirements are intended to be the cure.
 
The 2014 690.12 rules say that there has to be a way to make sure that there is less than 30V within 10 seconds of initiating shutdown on conductors within 10 feet of the array outside of the building or within 5 feet of the array inside of the building.
 
Rapid shutdown is accomplished 3 ways
1.    Inverter within 10 feet of the array will immediately shut down when ac power is no longer available to the inverter. This would include microinverters, ac modules or string inverters by the array.
2.    Power optimizers can perform rapid shutdown, because they are brains that can be controlled from down below. They need to be 690.12 compliant systems.
3.    A contactor is a remote disconnect that is powered from down below. Midnite solar and others make these switches that can be placed by the inverter shut-off switches and when the button is pushed, the array will be disconnected on the roof.
 
Warning: 2017 NEC Rapid Shutdown requirements will be stricter.
 
Thanks,
Sean White


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