AC300 powering APC UPS issue

When my APC UPS units are powered by my AC300 the APCs throw a wire fault warning.
But only when the AC300s provide power through the batteries. Whan the Grid powers is back on and the AC300 UPS routes the power from the grid to the APCs the fire fault goes away.
Anyone seen this issue ?

Check the ground connection . It may be open when the AC300 is supplying power from its B300 battery. I have several APC UPS devices, but I don’t have my AC300 yet to test that same fault.

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The issue is likely that neutral and ground wire is not bounded (they are floating independently) in the AC300 and therefore sophisticated electrical devices, like a UPS (or my TESLA car charger as an example) will throw a fault as it does not sense the connection of neutral and ground, like you would have in an electrical panel.

I made an easy solution for this. Purchased a male 120V plug at the hardware store and connected a small 14 gauge wire jumper between the neutral - make sure you know what is the neutral (the larger rectangular part) and the ground pin in the connector. Then I simply plugged it in to one of the receptacles on the AC200Max in my case. No issues of the devices throwing faults after that.

Just make sure to only do this if you are connecting directly to the loads, in your case the UPS. If you do this through a transfer switch into your regular breaker box, the bonding should already be done there and should NOT be done at the AC300. If it seems like the bonding is not done in your breaker box, I would call an electrician to sort it out.


thank you very much. This makes sense. I will give this a try. very helpful.

sorry i have a follow up.
Doing this works just fine when the battery kicks in. But what when the power is back and is routed through the AC300s outlets. would that shortening of ground and neutral do any damage when utility power is routed through the AC 3oo ?

No, it will not cause any damage. The ground contact is for safety and no current should be flowing through it.

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thank you so much. I don’t understand why bluetti not just route the ground from the grid power over to the ground plugs at the front outlets. It is already in the unit coming i n though the charge plug.

You will have to ask the Bluetti/MaxOak engineers that designed the AC300 electrical wiring. It may be that the Chinese use a different code than the NEC we use.

yes true. Will Prowse just did that on a delta Pro and fried it. once he put the unit back on the grid with it plugged in.

This configuration is actually true for most generators, even many gas generators do not have the neutral bonded with ground. Reason is that you should only have one ground to neutral connection per NEC and since the generator is portable you cannot guarantee where that location is. In this case, I agree with you though, the ground from incoming grounded charge wire, should in my opinion also carry over to the inverter.

Too bad, should not have damaged it. That may be a case of reverse polarity. Early AC200 units actually had that problem (see youtube), phase and neutral wires were swapped at factory. It does not matter off-grid which one is grounded, but if connected to grid and you have reverse polarity it will be a short circuit - fried equipment…