Plug in solar and GFIs

[peatmoss]

I'm seeing a lot of ads for plug in solar these days. The companies that promote it are saying plug your system into a GFI outlet. There is an old thread on here but its not really conclusive. https://forums.mikeholt.com/threads/can-you-back-feed-a-gfci-breaker-in-a-sub-panel.92576/

The schematic of a GFI shows there is a current sense coil over both hot and neutral lines. The way they work is if there is current outside these lines on return a current is generated in the coil. If you backfeed a GFI I don't see how it knows the difference as long as there is no current leakage.

What a ground fault circuit interrupter does and what it does not do | EEP

A ground fault circuit interrupter (GFCI) monitors the current balance between the ungrounded “hot” conductor and the grounded conductor.

electrical-engineering-portal.com

Anyone have experience or thoughts on this? How about GIF breakers?

 

[don_resqcapt19]

I approved this since it is not asking for DIY how to information.

 

[jaggedben]

I don't believe plug-in solar is actually legal anywhere in the US under utility rules, notwithstanding what ads might tell you. It's legal in parts of Europe, maybe it should be here too, but it's not.

As far as backfeeding a GFCI, there has long been the requirement in the NEC that circuit breakers be suitable for backfeed. (705.30(D) in the 2026 NEC). GFCIs have not typically been suitable for backfeed and a manufacturer's instruction that runs afoul of the NEC in this way is prohibited by the NEC and may not pass an inspection.

There are other safety issues that would make safe plug-in solar not really plug-in, as well.

The products you are looking at, do they say they're listed to UL1741? I have heard of some plug-in products maybe getting listed but I'm honestly a bit baffled at how that can be.

 

[peatmoss]

Thanks for the reply. It appears the new NEC requires it to specifically state it can be backfed.

Here is where I cam across it brightsaver.org/net-metering-expansion-backyard-solar

Their inverters are UL1741.

 

[winnie]

I don't believe plug-in solar is actually legal anywhere in the US under utility rules, notwithstanding what ads might tell you. It's legal in parts of Europe, maybe it should be here too, but it's not.

Utah has apparently passed a law that requires utilities to allow 'plug in solar'. I don't know the details. Press article:

Power To The People: Plug-In Solar Now Legal In Utah Homes - CleanTechnica

New legislation in Utah introduces a new category for small, portable solar generation devices, allowing residents to integrate plug-in solar systems into their homes more easily.

cleantechnica.com

 

[kwired]

The GFCI doesn't know which direction flow is coming from, it is only monitoring whether what current goes out on one conductor is coming back on other conductor(s) that are also protected.

GFCI's that have line/load reversal lockout (which is a listing standard for receptacle types AFAIK) usually will still function with it reversed but once tripped will not reset if supply volts is not on the actual line side.

 

[ramsy]

The GFCI doesn't know which direction flow is coming from

If it violates GFCI listing, or trips, there are duplex outlets without GFCI under most windows

There are other safety issues that would make safe plug-in solar not really plug-in, as well.

Without supplemental OCP, like reset button on most power strips, device or fixture wiring must be rated for 15A, or 20A branch circuits

If device uses a NEMA 5-15, any adapters to 2-prong outlets will violate listings, and NEC 250.114

If fire marshals find listing or safety code violations among the ashes, insurance Non-Renewal & Cancellation may result in total loss