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690.11 dc arc-fault protection brought to you by the 2011 NEC


Q:

Sean - so how do inverters handle those short fluctuations in current (irradiance)? Are there times when the inverters Arc Fault Protection mistake this short burst of current as an arc and shut down temporarily?

A:

Hi Chris,
690.11 Dc arc-fault protection first came out in the 2011 NEC and when states started adopting the NEC, nobody had figured out reliable dc arc-fault protection yet. There were many false trips on the original systems. Apparently this same thing happened with ac arc-fault protection when the Code required it.
After reliable dc arc-fault protection was available, then the AHJs started requiring it. The NEC allows for this and AHJs cannot require things that are unavailable.
Now dc arc fault protection is very reliable.
The quick decreases and increases in current from clouds and shading do not cause trouble with the inverters. There are some that think that clouds could cause troubles with a saturated grid and that is something that energy storage and energy management could fix if it were a problem.
There was a total eclipse in Germany about a year ago and there was big news about people forecasting that the shutting down of the PV systems will cause havoc on the grid. What happened is nothing, just like at sunset and just like Y2K.
Thanks,
Sean White


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