Micro Inverter and Plug and play inverter

ZakarumeZakarume Solar Expert Posts: 143 ✭✭
Micro Inverter and Plug and play inverter?

Are these safe to use? If so which 1 is safer?
1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter

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  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Micro Inverter and Plug and play inverter
    Zakarume wrote: »
    Micro Inverter and Plug and play inverter?

    Can you clarify a bit? There are (in the US):

    Central Inverters: big 3-10+ kWatt GT inverters connected via the high voltage DC wiring to a large solar array.

    Micro Inverters: small ~200-250 Watt GT inverter connected to a single (generally) solar panel--And ~17 or so of these inverters are connected to a 240 VAC circuit brought up to the roof.

    Plug and Play GT Inverters: generally smaller inverters (few hundred to 500 to 1,000 watt or so) GT inverters that are intended to plug into a nearby 120 VAC (usually) house hold standard three prong outlet.

    The first two (Central and Micro) GT inverters are UL/NRTL listed inverters classes and considered "safe" when installed correctly. You can argue which type is "safer" in the abstract (probably micro inverters are safer than central inverters due to issues with DC arc faults--DC current sustains arcs and can start fires much easier than similar AC voltages).

    And in the US/Canada, there is (as far as I know) no "legal" / UL / NRTL Listed plug and play GT inverters. The issue being that standard AC outlets cannot share AC loads (like in a bedroom or garage) and a GT Inverter power source. When a GT Inverter is plugged into existing wiring, you have the current from the AC breaker (typically 15 or 20 Amps) plus the current from the GT inverter (could be another ~12-16 amps from several GT inverters plugged into the same branch circuit. This means that you can pull ~27 amps or more and overheat your 14 or 12 AWG wiring).

    As far as I can see, there is no way to make plug and play inverters "code safe" in an existing home.

    Plus, because no Plug and Play GT inverters can get NRTL Listed--Their quality seems to be pretty poor and overheating failures seem to be pretty common with some vendors of P&P GT inverters.
    Are these safe to use? If so which 1 is safer?

    Central and Micro GT inverters are both "safe" if properly installed. I think (guess) that Central Inverters are possibly more reliable and easier to repair vs Micro Inverters (easier to fix one inverter on a garage wall, vs going on a roof to find/pull a failed micro inverter).

    On the other hand, as I said, DC Arc faults are a recognized safety issue with GT Solar Arrays (and NEC has worked to create Arc Fault remedies--Some better than others). Roof fires are uncommon with GT Systems, but they do occur. I would guess that Micro Inverters are going to be a bit "safer" or less likely to Arc Fault/start and start a fire that way (again guessing).

    It is possible, if you do it right (more discussion needed), for a plug and play inverter to be installed correctly/safely. But you could not do it per code and not get a signed off building permit (and legal GT agreement with most utilities). I would not suggest that anyone use P&P GT inverters.

    Does the answer your questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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