You are having problems with the ground conection in the outlet in wich you have pluged the UPS.
You must call an electrician! But before you may want to try conecting the UPS in other outlet to vheck, or replace the input cable.
If the problem is in the outlet, the reason could be the conection inside the outlet box or in other splice-box from wich the outlet line was feeded. On the other extreme, the problem could be in the electrical pannel.
If the problem occurs in every outlet the problem could be the neutral-to-ground bonding.
If you need future help just letme know!
Jose P. Mir.-
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Jose P. Mir
jpm@jpmir.net