I have been looking at an APC 3000VA and 7500VA 240V SmartUPS's and have notice that the inverter output has a floating neutral. When either UPS is in bypass mode running from mains they have the normal MNE readings but when the output is coming from the batteries or if the 7500VA is set the full double conversion mode the neutral measures between 90-120 volts to earth and the active is 160-120 volts to earth. With no load the neutral reads about 90 and active 150 but the balance out to 120 each way once there is a load.
I believe this is due to the way the inverter circuit works where the +48v DC from the battery is connected as 0v AC and the the battery DC negative is flicked between the high and low to give 96V AC which is then fed through smoothing circuit, transformers, etc.
Should the inverter output have a neutral earth bond, I fear this would likely the damage the inverter.
Interested to hear other thoughts on this.
Regards,
Jordan
I have no direct experience with APC UPS' of that size.
But on the couple of UPS's that I have wired up in that size range they have been terminal strip for the connections.
And depending on what output voltage you want (straight 120 volts, 120v/240 split phase, 240 or 208) you can connect things to different terminals. One of the options is if you want a neutral to ground Bond.
Depending on which output voltage configuration you use the neutral to ground Bond would need to be on different connections so it could be left out from the factory.
Again this is all just my past experience with UPS is in that range. I have no idea what UPS you have. Take all of this with a grain of salt.
I would consult the manual for your ups and see what options it lists.
Sent from my Nexus 6 using Tapatalk