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I have a Reliance ProTran2 manual transfer switch plugged into my Bluetti AC300 battery backup system which has a floating ground.

The AC300 is supposed to be used as a UPS backup system and pass grid power through the AC300 and then when grid powere goes off, it switches over to the battery. The AC300 has a switch to turn on AC output.

PROBLEM: If I plug the AC300 into grid power, with the AC output turned off, it charges up the batteries with no problem. As soon as I turn on the AC output, the GFCI circuit breaker that I have the AC300 plugged into pops. This happens no matter how I have the Transfer switches set in the ProTran2. They can all be set to Grid, neutral or Gen with same result.

If I unplug the AC300 from the grid, I can switch any or all of the ProTran2 switches to GEN and have power with no problem.

I have seen others who did the same thing without pluggibg into the grid without using a GFCI plug actually fry their AC300. The talk is that a different type of manual transfer switch is needed but no definite brand or model is specified.


We are not wedded to the transfer switch but are to the Bluetti AC300 battery backup system. I have asked the manufacturer to give me the name of a transfer switch that will definitely work and I'm waiting for a response.


The transfer switch was installed by an electrician specifically for the backup system and the backup system is supposed to be used as a UPS backup system with grid power being passed through and when grid goes out, the system is supposed to switch over to the battery.

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  • Imagine some grid power(a few volts/milli amps) is being pass though plus the battery power and it is enough to trip/confuse the GFCI. It is suppose to work with grid power being completely off/out.
    – crip659
    Jul 3 at 18:33
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    Was this transfer switch installed specifically for it? Who specced the transfer switch? Jul 3 at 18:40
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    After looking at it quickly it it touted as a UPS / solar backup system but it sounds like there is an issue when trying to provide a true output while on grid, this could be from the different sources not being tied at the same ground potential so there is an imbalance and this caused the GFCI to trip. I have seen (computer)switching supplies have issues when the neutral was at a higher level than the communications grounding including frying the computers, this was on the same source not a separately derived system, in this case you may have to switch your neutral so the inverter can be grou
    – Ed Beal
    Jul 3 at 19:11
  • Continued, so the inverter ground is at the same point and not a parallel path. In short what I think is happening is there are 2 different levels of ground and this alone can cause the imbalance if the inverter has both a floating output and a solidly grounded input with the control electronics running on the output side but being charged by the input if that makes sense. Or this would be my first place to check.
    – Ed Beal
    Jul 3 at 19:17
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    Thanks, but please don't post responses as answers. These should be posted as comments, or relevant details edited into your question. Now is there some reason you NEED to have the Bluetti both plugged in to charge, and also attached to the transfer switch at the same time? Can you add SIGNIFICANT detail as to what exactly you have and how it is wired? Jul 3 at 23:17

2 Answers 2

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You can't double-plug it

What you want is to leave it both plugged in to charge, and plugged in to feed the house, all the time 24x7. You can't do that. (at least not without some kit).

You need to unplug the charger before plugging into the transfer switch. And vice versa.

And since you have a manual transfer switch anyway, that's not a huge inconvenience for you. Oh. Hey. Did you know that??? This thing is NOT automatic. You must manually throw it over.

The reason this is necessary is faults (cheapness) in the machine's design, where they didn't bother to isolate things they could and probably should have isolated. (namely: neutral from input to output). You could work around it with an isolation transformer (NOT to be confused with a step-down transformer).

"I can make it work if I plug it into a Non-GFCI outlet" yeah, but it's still a dangerous Code violation if you do. Just the GFCI has been "keeping you honest".


The lack of isolation where isolation is needed tells me either it was never UL Listed (because UL would never approve "leaving that bit out" like that). Or, you are using it contrary to its instructions, which is a Code violation NEC 110.3. I don't see anything in the instructions that says to leave both the charge and feed connections connected at once, except in one diagram where you are using their subpanel, but maybe that subpanel fixes the isolation problem.


I don't know if you're trying to feed this panel as 120/240V split-phase... but that is NOT easy to do with this inverter, and requires significant additional kit from them, like 3x the gear you have now. It is likely possible to wire the ProTran to work in 120V-only mode.

As an observation, I note we often see people try to pull off battery systems with too little knowledge and too much money (yet, not enough money to hire a competent pro to do it "soup to nuts"). A competent pro will force you to use better quality/pricier stuff, because they have to stand behind it. And then, it will just work. You must either learn the knowledge, pay experts, or buy products with the expertise built in, such as a Tesla PowerWall.

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After looking at the mfg info. it is touted as a UPS / solar backup system but it sounds like there is an issue when trying to provide a true output while on grid.

this could be from the different sources (code calls them separately derived sources) not being tied at the same ground potential so there is an imbalance and this caused the GFCI to trip.

I have seen (computer)switching supplies have issues when the neutral was at a higher level than the communications grounding including frying the computers, this was on the same source not a separately derived system,

in this case you may have to switch your neutral so the inverter can be at the same point and not a parallel path.(or provide a 1:1 transformer to feed the charging side this isolates the primary and the secondary’s are connected no imbalance)

In short what I think is happening is there are 2 different levels of ground and this alone can cause the imbalance if the inverter has both a floating output and a solidly grounded input with the control electronics running on the output side but being charged by the input if that makes sense. Or this would be my first place to check. Creating the isolation is how some hospitals eliminate this issue in operating rooms.

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