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4.7.2 Input/output over current protection and wire sizing
The cabling of the UPS system has to be sized according to the UPS power rating.
Sizing of circuit Breakers, Fuses and cables for Input Utility, output load and Battery must meet the requirements
of local and national electrical codes.
Before connecting the UPS, verify that the Utility Voltage and Frequency, the Output Load Voltage and Frequency
and Battery Data (cells number, floating voltage, autonomy) are according to the required data.
The protection of the UPS Utility input must be exclusively with 3 pole breakers.
In 4-wire distributions (3-phase, 4-wire plus ground):
• Disconnection of the Neutral is not permitted.
The UPS needs the connection of the Neutral to the input, to guarantee the function in TN mode (Neutral-
Earth).
• Caution when using Four-Pole Circuit Breakers as protection to the UPS Load.
A potential problem exists for situations with non-linear Loads, causing the Neutral Current to be higher than
the Phase Current.
Avoid to run the input cables in parallel with the output cables to prevent them from noise induction.
The Three-Phase Utility Power supply must be symmetrical with respect to Ground (wye-connected and grounded
solidly), due to the existence of voltage surge protection devices inside the UPS.
The connection of the Battery to the UPS must be protected with fuses or similar devices according to technical
specifications and in accordance with local standards.
Note!
If you use ELCB breaker (Earth Limiting Circuit Breaker) to protect the input connections, consider
the high leakage current generated by the noise suppression capacitors.
If these ELCB breakers are strictly necessary, we suggest using the largest type suitable for non-
linear current and for delayed operations.
Specific prescriptions apply for 3-wire (3-phase plus ground) distributions; refer to the specific
section for details.
To ensure the circuit selectivity in case of Short- Circuit in the Load equipment, special care must be taken in
choosing the Fuse or Circuit Breaker ratings installed in the output distribution circuits.
Due to the relatively low short-circuit capability of the UPS Inverter, a short-circuit in the Load will cause an
immediate transfer to Utility.
The largest fuse in the output distribution should be at least 1.6 time smaller than the Fuses supplying the
Bypass line.
If circuit selectivity is required while the Load is fed from the Inverter (Bypass Utility not available), the Largest
Fuse or Circuit Breaker should be rated at no more than 20% of the UPS Output Current Rating.
Note!
The delivery and installation of fuses and input/output connections of the UPS are at the
customer's expense, unless agreed otherwise.
TLE Scalable Series 40 to 150 UL S1
UPS Installation Guide / REV-B
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