The Most Common Violation for PV systems and MLO Sub-Panels

[jar546]

What do they both have in common? Very often back-fed circuit breakers. In the PV, the inverter feeds a house panel via a back-fed breaker, and with sub-panels, sometimes people just don't like using the lugs of an MLO. There are other installations that can create this situation.

NEC 408.36(D)
(D) Back-Fed Devices.
Plug-in-type overcurrent protection devices or plug-in-type main lug assemblies that are back-fed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panelboard.

This is why I prefer commercial work and bolt-in breakers.

Based on the brand, this can be fixed for under $3

 

[wwhitney]

Breakers backfed by listed interactive power sources, such as any grid-tied only PV inverters, are exempt from 408.36(D) per (2020) 705.12(E). Pop such a back-fed breaker off the bus, and you won't have energized bus terminals on the breaker.

Cheers, Wayne

 

[jar546]

Breakers backfed by listed interactive power sources, such as any grid-tied only PV inverters, are exempt from 408.36(D) per (2020) 705.12(E).

Absolutely, and we see more and more interactive power sources in PV systems. I was schooled on that about 5 years ago by a PV installer after I failed the inspection and then read the interactive section.

 

[wwhitney]

Absolutely, and we see more and more interactive power sources in PV systems.

So it's not a common violation for PV systems, it would require an inverter that is designed to operate in grid-forming mode.

Cheers, Wayne