If you use the device as ups, follow the manufacturer's instructions regarding installation and safety.
http://www.apc.com/salestools/EALN-79CR5M/EALN-79CR5M_R3_EN.pdfhttp://www.apc.com/salestools/ASTE-6Z8LUC/ASTE-6Z8LUC_R11_EN.pdfAs far as rcd protection is concerned, a customer asked me this question while I was working for a major industrial UPS manufacturer.
Indeed, according to the standards of low-voltage installations in Belgium, protection by 30mA rcd is mandatory.
However, exceptions are provided, and critical load feeding is one of those exceptions.
In addition, a UPS generates many harmonics and therefore requires a heavy input filter.
During transients of the input voltage, this filter can cause a peak current to earth sometimes greater than 30 mA and thus cause unwanted triggering of the rcd .... This is not compatible with the function of a UPS .
Similarly, it is not recommended to install an output rcd from the UPS depending on whether it is supplying a critical load that can not be unexpectedly interrupted.
So, unless local regulations and laws dictate, no rcd with the UPS.
On the other hand, if you use the UPS as a simple UPS running on battery without connection to the power grid, the rules applying to UPS no longer apply.
It will first be necessary to check if such operation is possible.
Other problems arise: Can the battery be grounded?
Can the ac output be grounded too?
One may wonder if it is interesting to put the output ac to the ground.
In a low-voltage installation, the neutral of the high-voltage transformer is always grounded for obvious safety reasons.
Indeed, in case of transformer insulation fault, the high voltage could end up on the low voltage network if there was no secondary grounding.
But in this case, such a risk does not exist.
Therefore, I advise not to ground the output of the inverter.