P54x/EN AP/La4 Application Notes
(AP) 6-88
MiCOM P543, P544, P545 & P546
AP
7. HIGH BREAK OUTPUT CONTACTS
The high break contacts allow the elimination of auxiliary relays. This in turn helps in the
provision of cost effective solutions, minimizing space, wiring, commissioning time, etc..
According to the model selected, in addition to standard output relay boards, one or two ‘high
break’ output relay boards can be fitted. Each houses four normally open output contacts
suitable for breaking loads higher than can be broken with the standard contacts. The
performance and possible application scenarios of these contacts are described in the
Technical Data (TD) and Firmware Design (FD) chapters of this manual.
8. AUXILIARY SUPPLY FUSE RATING
In the Safety section of this manual, the maximum allowable fuse rating of 16 A is quoted.
To allow time grading with fuses upstream, a lower fuselink current rating is often preferable.
Use of standard ratings of between 6 A and 16 A is recommended. Low voltage fuselinks,
rated at 250 V minimum and compliant with IEC 60269-2 general application type gG are
acceptable, with high rupturing capacity. This gives equivalent characteristics to HRC "red
spot" fuses type NIT/TIA often specified historically.
The table below recommends advisory limits on relays connected per fused spur. This
applies to MiCOM Px40 series devices with hardware suffix C and higher, as these have
inrush current limitation on switch-on, to conserve the fuse-link.
Maximum number of MiCOM Px40 relays recommended per fuse
Battery nominal
voltage
6 A 10 A fuse 15 or 16 A fuse Fuse rating > 16 A
24 to 54 V 2 4 6 Not permitted
60 to 125 V 4 8 12 Not permitted
138 to 250 V 6 10 16 Not permitted
Alternatively, miniature circuit breakers (MCB) may be used to protect the auxiliary supply
circuits.
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