CHAPTER 3: INSTALLATION WIRINGL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-1333.3.2 Dielectric strengthDielectric strength is the maximum electric strength that can be sustained without breakdown. It is measured in volts.The table shows the dielectric strength of the UR-series module hardware.Table 3-1: Dielectric strength of UR series modules3.3.3 Control powerThe power supply module can be ordered for two possible voltage ranges, and the L90 can be ordered with or without aredundant power supply module option. Each range has a dedicated input connection for proper operation. The rangesare as follows (see the Specifications section of chapter 2 for details):• Low (LO) range — 24 to 48 V (DC only) nominal• High (HI) range — 125 to 250 V nominalThe power supply module provides power to the relay and supplies power for dry contact input connections.The power supply module provides 48 V DC power for dry contact input connections and a critical failure relay (see theTypical Wiring Diagram earlier). The critical failure relay is a form-C device that is energized once control power is appliedand the relay has successfully booted up with no critical self-test failures. If on-going self-test diagnostic checks detect acritical failure (see the Self-Test Errors section in chapter 7) or control power is lost, the relay de-energizes.For high-reliability systems, the L90 has a redundant option in which two L90 power supplies are placed in parallel on thebus. If one of the power supplies becomes faulted, the second power supply assumes the full load of the relay without anyinterruptions. Each power supply has a green LED on the front of the module to indicate that it is functional. The critical failrelay of the module also indicates a faulted power supply.Module type Module function Terminals Dielectric strengthFrom To1 Power supply High (+); Low (+); (–) Chassis 2000 V AC for 1 minute1 Power supply 48 V DC (+) and (–) Chassis 2000 V AC for 1 minute1 Power supply Relay terminals Chassis 2000 V AC for 1 minute2 Reserved N/A N/A N/A3 Reserved N/A N/A N/A4 Digital contact inputs/outputsAll Chassis 2000 V AC for 1 minute5 Analog inputs/outputs All except 8b Chassis < 50 V DC6 Digital contact inputs/outputsAll Chassis 2000 V AC for 1 minute7 G.703 All except 2b, 3a, 7b, 8a Chassis 2000 V AC for 1 minuteRS422 All except 6a, 7b, 8a Chassis < 50 V DC8 CT/VT All Chassis 2000 V AC for 1 minute9 CPU All Chassis 2000 V AC for 1 minuteFilter networks and transient protection clamps are used in the hardware to prevent damage causedby high peak voltage transients, radio frequency interference (RFI), and electromagnetic interference(EMI). These protective components can be damaged by application of the ANSI/IEEE C37.90specified test voltage for a period longer than the specified minute.Control power supplied to the relay must be connected to the matching power supply range of therelay. If voltage is applied to the wrong terminals, damage can occur.The L90, like almost all electronic relays, contains electrolytic capacitors. These capacitors are well-known to deteriorate over time if voltage is not applied periodically. Deterioration can be avoided bypowering up the relay at least once a year.
