MicroLogic Trip Unit Accessories

External Neutral Current Transformer (CT)

The sensor is installed on the neutral conductor for neutral protection and metering and residual current ground-fault protection for equipment.

For SGR System: The sensor is installed around the connection of the transformer neutral point to ground and connects to the MicroLogic 6.0A, 6.0P or 6.0H trip units. SGR requires a modified differential ground-fault (MDGF) sensor and MDGF interface module to connect to the trip unit.

For MDGF System: An MDGF sensor is installed on each phase and neutral of each circuit breaker and connects to the MicroLogic trip unit through an MDGF module. See MDGF Instruction Bulletin 48049-182.

Toroidal Current Transformers (CTs) for W-Frame Circuit Breakers

Metering current transformers are optional and are mounted on the NW UL or ANSI cradle. They permit connection to the standard metering device. All metering transformers are accurate with the 0.3% accuracy class, 5 A output ratio at full load (for example, a 1600 A metering CT would send 5 A at the full load of 1600 A). A standard wiring harness is also included for factory-installed MCTs. Not available for neutral pole on a four-pole circuit breaker. Not available on cradles with ArcBlok technology.

Voltage Measurement Inputs

Voltage measurement inputs are required for power measurements. As standard, the trip unit is supplied by internal voltage measurement inputs placed on the bottom terminals of the circuit breaker. On request, the internal voltage measurement inputs may be replaced by an external source.

Adjustable Rating Plug

Eight interchangeable rating plugs are available to limit the long-time threshold setting range for greater versatility.

External Power Supply Module

Power supply modules are available in six input voltages: 24/30 Vdc, 48/60 Vdc, 125 Vdc, 110/130 Vac, 200/240 Vac, and 380/415 Vac (all +10%, -15%). The output voltage for each is 24 Vdc; the output power is 5 VA/5 W (ripple < 5%). The modules are not UL Listed.

When used with the MicroLogic A, P, and H trip units, a power supply module makes it possible to:

• Display currents less than 20% of sensor (I_n).

• Maintain display of tripping causes after opening of the circuit breaker (P and H trip units only).

• Store the value of the interrupted current (P and H trip units only).

• Power the M2C module (P and H trip units only).

External Battery Backup Module

The external battery backup module provides up to 12 hours of backup power for the power supply module.

M6C Programmable Contact Module

M2C Programmable Contact Module

These contacts are used with the MicroLogic P and H control units, and indicate the type of fault and instantaneous or delayed threshold overruns (i.e trip unit protection pick-up, current/voltage unbalance, under/over voltage, reverse power, phase rotation, under/over frequency, and load shedding). The M2C unit is powered from the control unit’s 24 Vdc source (100 mA consumption); the M6C unit requires an external 24 Vdc power supply (100 mA consumption).

They are programmed via the control unit using a keypad or via a supervisory station with the COM communication option. They may be programmed:

• with instantaneous return to the initial state;

• without return to the initial state;

• with return to the initial state following a delay.

Zone-selective interlocking (ZSI) is used to reduce the stress on electrical distribution equipment during fault conditions by reducing the time it takes to clear the fault, while maintaining system coordination between overcurrent protective devices.

During a short-circuit or ground-fault condition on a ZSI system, the device directly ahead of the fault sends a signal upstream via control wiring to restrain upstream circuit breakers from tripping and then trips with no intentional time delay to clear the fault. Upstream devices which receive a restraint signal obey their short-time and/or ground-fault delay settings to maintain coordination in other areas of the system. Upstream devices that do not receive a restraint signal trip with no intentional time delay.

For ZSI to work, trip settings must be coordinated so a downstream circuit breaker will trip before an upstream circuit breaker under overload, short-circuit or ground-fault conditions. (Effective coordination requires a system coordination study.)

Fault 1—The upstream circuit breaker (A) will clear the fault with no intentional delay, regardless of its time-delay setting. Fault 2—Circuit breaker (B) will inform upstream circuit breaker (A) that it is clearing the fault. This will prevent circuit breaker (A) from tripping instantaneously. Circuit breaker (A) will trip at the end of its time delay setting if the fault is not cleared during this time.

Restraint Interface Module (RIM)

The restraint interface module (RIM) is used to allow zone-selective interlocking communications between circuit breakers with old Square D MicroLogic, Merlin Gerin™, or Federal Pioneer™ trip units and GC series ground-fault relays.

Downstream circuit breakers with MicroLogic 2.0A, 5.0A, 5.0P, 5.0H, 6.0A, 6.0P, and 6.0H trip units can restrain up to 15 upstream circuit breakers with MicroLogic 5.0A, 5.0P, 5.0H, 6.0A, 6.0P and 6.0H trip units without requiring a restraint interface module. If the number of upstream circuit breakers exceeds 15, then a RIM is required.