UL 1703 When do I use the 125% factor for MAX OC on a PV string?

[Stuart Cooley]

Our inspectors contend that to compute Maximum Open Circuit Voltage on a string of photovoltaic panels, you take the Max. OC voltage of the panels added together, multiply by 125% (before ANY calculation he says, and here he is citing UL 1703) and then apply any other calculations, which in our case is a 1.1 X factor for the 33 deg F "cold" temperatures here in Santa Monica. That calculation exceeds 600 V for a 7-module string of 63.8V modules.

Is this an NEC safety factor? Is it applied correctly in this case?

Do other jurisdictions apply the 125% in cold climate conditions as well as operating current situations in warm climates?

Thanks for any (quick) response.

-Stuart

 

[tom baker]

Thats a great question and if you don't get an answer try John Wiles he writes for home power mag and is the principle author of the PV article in the NEC.