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OPM_LPS_33E_60K_M12_2GB_V010.doc
Operating Manual
LP 33 Series 60-80-100-120 kVA / S2
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
.