High Earth voltage at Smart UPS Output on battery operation

[Anonymous user]

I understand after reading APC support (FAQ FA156549) but is it possibel to to reduce the output Earth voltage(Between Netral to Earth) for client satisfaction after doing some hardware changes with Earth, Netral or Using separate Earth or some component network?

Mukhtar

[BillP · Accepted solution]

While "On Battery," safety agencies (UL, VDE, etc.) require the UPS input connections to be disconnected from the utility input to prevent "backfeed" power/voltage from the UPS batteries being applied to the UPS input terminals. Because the Neutral must also include this "backfeed" protection (we do it by opening a relay), the output Neutral to Ground voltage will "float" to approx half the voltage between output Line & Neutral. For a 230Vac system, the N-GND voltage can be 115Vac.  This does not become a safety hazard because the output L & N conductors are not user-accessible.  They are both always considered "high voltage" conductors.

If the UPS output must have a N-GND connection for zero volts while the UPS is "On Battery," an output isolation transformer must be attached to the UPS output so that a new N-GND connection can be made without creating a ground loop. We sell isolation transformers that can be used for this, if required.