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Hello all,
Before I read the manual for my 6kW LF inverter, I had thought wiring the inverter to a distribution/breaker box/panel was pretty straightforward: L1 & L2 to the respective sockets on the main breaker, and N(eutral) to the ground bar.
But the "CRITICAL WARNING FOR 240V AC INPUT" on page 8 of the manual (v1.1r4) gave me a little pause. I have no intention of connecting anything to the AC input on the inverter, because it is only going to receive DC power from the batteries. So perhaps I can safely ignore the warning. But since I'm not sure of ALL the implications of "the ubiquitous (and generally required) ground-neutral bonding on breaker panels" for my simple, off-grid setup, I wanted to consult with wiser heads before I proceed.
Let me reiterate/summarize: this is a purely off-grid setup through a standard household split-phase distribution/breaker box, fed ONLY by battery DC going through the inverter. Is my initial wiring assumption correct (see my first sentence above)? Or is there an extra step/part needed?
Thanks in advance for any advice,
Rob
Before I read the manual for my 6kW LF inverter, I had thought wiring the inverter to a distribution/breaker box/panel was pretty straightforward: L1 & L2 to the respective sockets on the main breaker, and N(eutral) to the ground bar.
Yes, that would be correct.
Let me reiterate/summarize: this is a purely off-grid setup through a standard household split-phase distribution/breaker box, fed ONLY by battery DC going through the inverter. Is my initial wiring assumption correct (see my first sentence above)? Or is there an extra step/part needed?
Yes, you are correct.
Quick question: which version control board does your inverter have? (STAT page, 2nd line should say A.1, B or C.)
The warning there on 1.1r4 (last firmware version before Rev. C!) had to do with a bit of shortsighted design...actually a shortsight that is in a LOT of Chinese LF inverters. The GS Rev A.1 and Rev. B boards only have a single pole relay for AC input disconnect. That's fine for most of the world with single-phase electricity (220 or 110). The issue comes with split-phase systems, where 3 wires are often presented to the inverter on AC input (whether on purpose or inadvertently)--and at least two of the 3 wires have to be disconnected in order to stop power flow.
That was what the warning was about. The solution was to ensure that there were no more than 2 Mains potentials connected to the inverter--and that way, it could be disconnected with the single pole relay.
I learned very quickly...Rev. C has a double-pole relay on it, and the restriction no longer applies.
If you purchased the inverter within the past few months, it should have a Rev. C control board in it. But it's good to check just to be sure 😉.
Hey, thanks for the quick reply! I haven't powered up the inverter yet, but I purchased it last year. So it's probably not Rev. C. But if I read you right, it won't matter in my use case.
Correct, if you are not utilizing AC input, then it will be just fine connected to a breaker panel in the logical manner 😉.
Just make sure you don't inadvertently dump AC mains into the output of the inverter...they tend not to like that.
By the way, I wanted to check one other minor detail. Assuming I removed the software safety governor and occasionally ran 7-8 kW through the house, if I did the math right and consulted the right wire gauge charts, I would only need 10AWG copper from the inverter to the breaker? I know the 240V is what accounts for it, but it stills seems awfully thin compared to all the other wiring in my PV-controller-battery-inverter system. Does 10 sound about right?
Wire gauge has a lot of factors to consider. Temperature rise, cable environment (free air, in conduit, direct bury etc), ambient temperatures, voltage drop over the run etc, duration of peak loading (ie, how long the wire is experiencing maximum rate of heating). 8kW at 240V is about 34A. 10AWG copper with insulation rated to 90c will do 40A. That doesn't mean you can put 40A through it and expect happiness.
You have to go back and consider all those other aspects plus add in your area's regulatory requirements on top of that. For example I can put 15A over 1.5mm2 copper in free air with 90c rated insulation and the cable will be happy. Regulation wise, not so much. The earthing requirements demands 2.5mm2 wire and for practical purposes that means I need to purchase cable where all 3 conductors are 2.55mm2 because no one makes 2x1.5+ 1x2.5 cable, it'd be silly to do it.
By the way, I wanted to check one other minor detail. Assuming I removed the software safety governor and occasionally ran 7-8 kW through the house, if I did the math right and consulted the right wire gauge charts, I would only need 10AWG copper from the inverter to the breaker? I know the 240V is what accounts for it, but it stills seems awfully thin compared to all the other wiring in my PV-controller-battery-inverter system. Does 10 sound about right?
Inverter has 10AWG wire internally--so no matter what's external, there's still 10AWG inside.
This little website gives a conservative (i.e. 60C rated, cable w/ 10AWG) ampacity of 30A * 240v = 7200W. If your wire has a higher temperature rating, you'd be able to run more amperage through it.
In the US, the electrical code restricts 10 AWG wire to 30 amps except in a narrow range of circumstances such as motors and air conditioning equipment. And then, there are de-rating factors to adjust for ambient temperature and number current carrying conductors in conduit. But generally, for the average home install, 30 amps is the max.
It's been awhile since I started this topic/thread, but I thought I'd post an update and a follow-up question.
Update: After swapping out a damaged display (thanks Sean & co), I wired the inverter to the main panel for the house, and everything works like a charm.
Question: The neutral and ground bus bars in the main panel are bridged together, which I understand is a common practice. However, they are not directly connected to the grounding rod. As best I can tell, all the end outlets/sockets/etc have individual ground wires that come together on a separate grounding bar which (in turn) connects to the grounding rod outside. My question is a two-part, contingent one:
A) Should the bridged neutral-ground bus bar(s) ALSO be directly connected to a grounding rod?
B) If the answer to A) is yes, is it okay - or even preferable - to connect it to the SAME separate grounding bar that leads to the SAME grounding rod as described above?
Thanks for all the helpful advice so far, and any more to come,
Rob
A) Should the bridged neutral-ground bus bar(s) ALSO be directly connected to a grounding rod?
According to grounding requirements, ideally yes. I'm not exactly on good terms with grounding--but that's the general idea, anyway.
You only want a single ground-neutral bond point in the entire system. (This is to prevent ground loops.) Systems that switch power out and in may need a ground bonding relay setup to avoid multiple ground-neutral bond points.
B) If the answer to A) is yes, is it okay - or even preferable - to connect it to the SAME separate grounding bar that leads to the SAME grounding rod as described above?
If I'm understanding correctly that all the outlet grounds are tied to a ground rod SEPARATE from the main panel--then yes, the ground bar inside the breaker panel should be connected to the same ground rod. Ideally, all the outlet grounds would tie to the ground bar inside the breaker panel...which would go to a ground rod. Unless there's something we're missing, the outlet grounds shouldn't be connected to a ground outside the breaker panel!