690(A)(1)(2) Photovoltaic Source Circuit Currents


New User
San Francisco
Project Engineer
As of late, I have come across this article and I'm not 100% sure how to apply it to the protection calculation. The following is the final part of the article listed in the title.

The calculated maximum current value shall be based on the highest 3-hour current average resulting from the simulated local irradiance on the PV array accounting for elevation and orientation. The current value used by this method shall not be less than 70 percent of the value calculated using 690.8(A)(1)(1).

My questions are, can someone provide detail as to why 70% is considered here? Also, going forward with the calculations, how would l calculate the protection, should I still do a multiplier of 125% twice for the DC, is another method considered here for protection?


Senior Member
They allow you to calculate an alternative value for 1.25*Isc, and then subsequently use this value in place of everywhere else you would use 1.25*Isc. This includes 1.25*(1.25*Isc), to size the OCPD, when we replace what I've put in the parentheses. One of the 1.25 factors still applies, as it is the continuous load factor that applies to every standard rated OCPD. It is the other 1.25 and Isc that I grouped, that has the opportunity to get replaced with your simulated value. The calculation that is a safety factor for a "super sun" (i.e. >1000 W/m^2) of irradiance being incident on the array.

You still can use the 1.25*Isc calculation as you always have been doing. Its just that this allows you the possibility of reducing it, if it is worth it to you to jump through a few extra hoops in your design effort. If it is not worth your effort, just go with 1.25*Isc.

The compounding of the 1.25 and 0.7 factors becomes 0.875. So "shall not be less than 70 percent of the value calculated using 690.8(A)(1)(1)" is an indirect way of saying "shall not be less than 0.875*Isc". What this is saying, is that there is a limit to how much you can take credit for your simulation calculation of maximum continuous current. Put your modules "in the basement", and your "max continuous current" is still no less than 0.875*Isc.