inverter fused inputs


Senior Member

I am designing a job with traditional string inverters and was asked about the fused input rule. It has been a long time since I have been asked or have needed to be concerned with that code rule, which I think has since been taken out of the code? There is an inverter we are working with that is a 50kw and allows for 12 string inputs, 2 strings per MPPT circuit input. It is the SMA Core1. I thought the old code was a maximum of 3 string inputs into the inverter. Can somebody help me out with this and reference a code section for me to give to the plan checker?

Thanks ahead of time for your help!


Senior Member
AFAIK the code never specified a max number strings. What it said was that you needed overcurrent protection on source circuits unless (exceptions) there were no parallel sources (one string, no batteries) or all wiring and equipment is rated for the sum of parallel sources. Practically speaking, this meant you could do two, maybe three strings without upsizing wire. The max fuse rating of the solar panels sets a limit on how many parallel strings you can have.



Senior Member
The code does not say how many can be put in parallel without OCPD, it just provides guidance on how to determine how many based on the equipment you are using. It's usually limited by the PV module series fuse rating and with modern modules, the limit is usually 2 strings in parallel without having to add fuses. Go back 10 or 15 years and there were modules with much higher series fuse ratings and you could get up to 4 or 5 strings in parallel before needing fuses. The good old days.