OPM_LPS_33E_10K_30K_4CN_V010.doc 27/82 Operating Manual LP 33 / 10-20-30 kVA
4.7.1 Fuse discrimination (co-ordination of breakers tripping)
In order to ensure the circuit selectivity in case of short- circuit at load level, special care must
be taken in choosing the fuse ratings installed in the output distribution.
When a short-circuit on the output occurs, if the mains voltage does not exceed the admitted
tolerances, the load is instantly transferred to the mains through the automatic bypass, taking
advantage of the higher short circuit power.
To ensure a correct co-ordination of the breakers tripping, the fuses supplying the bypass line must
be at least 1,6 time bigger than the largest fuse in the output distribution.
If the selectivity must be ensured also in case of mains failure (that means inhibit automatic
bypass), the largest fuse in the output distribution must be lower than 20% of the UPS rated
current for each phase.
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