POWER LINE AND DATA LINE SPD PROTECTION – SELECTION TIPS
The Power line SPD and Data line SPDs have distinct selection principles compared to fuse/MCBs, as well as different selection criteria. Data line SPDs include all SPDs other than power line applications — viz. Communication, Instrumentation, Voice, data, Ethernet, RS 485, RS 422, etc.
Power Line — Most power line protectors used in AC power low voltage applications, especially those used in Main DB & Sub DB, are connected parallel to the load. Low voltage means any AC RMS voltage from 1V to 1000 V and DC up to 1500 V.
Data Line — All data line protectors are connected in series to the load, though the basic protection components (GDT, MOV, SAD) are always connected in parallel. In data line SPDs, the series component — generally resistors or inductors — determines the load current that can pass through the SPDs.
Power Line SPD Selection Criteria
- Voltage Protection level (Up) based on Voltage withstanding level of the equipment (Uw) — ensure Up is lower than Uw in all cases
- Nominal Discharge current
- Maximum Discharge Current
- Impulse current (for Class I SPDs only)
- Tested as per IS/IEC 61643 for Class 1, Class 2 & Class 3 applications
- Response time
Other features to consider for ease of maintenance: Pluggable modules, Local indication of failure, Remote indication of failure, DIN-RAIL mounting.
Data Line SPD Selection Criteria
Data line SPDs selection criteria is based on sub-category, but all are tested as per IS/IEC 61643-21.
- Instrumentation line protection: Control room side SPDs — DIN rail mountable, spring loaded terminals; Field side SPDs for 2-wire & 4-wire applications
- RS 232 line SPDs: Suitable for 9 PIN, 15 PIN & 25 PIN SPDs (male-male, female-female & male-female)
- RF Co-axial line protection SPDs: Consider signal amplitude, frequency band, connector type, gender type, voltage protection level, insertion loss/return loss/NEXT
Though selection of SPDs is important, installation is more crucial because SPD installation is different from Fuse/MCB installation.
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