Fuse Discrimination (Co-Ordination Of Breakers Tripping) - GE LP 33 Series Operating Manual

5.7.1 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.
Modifications reserved Page 33/103
OPM_LPS_33E_60K_M12_2GB_V010.doc Operating Manual LP 33 Series 60-80-100-120 kVA / S2