Question 1

How do I select the correct NZM frame size for my application?

Accepted Answer

Select the frame size based on the required rated current and breaking capacity. NZM1 covers up to 125 A (50 kA at 415V), NZM2 up to 300 A (150 kA), NZM3 up to 630 A (120 kA), and NZM4 up to 1,600 A (65 kA). The frame size determines the physical dimensions and maximum ratings. Within each frame, specific current ratings are selected via the trip unit. Electronic trip units (available for NZM2-4) provide adjustable protection curves for precise coordination.

Question 2

What is the difference between thermal-magnetic and electronic trip units?

Accepted Answer

Thermal-magnetic trip units use a bimetallic strip (overload) and electromagnetic solenoid (short circuit) with fixed or limited adjustment ranges. They are reliable and require no power supply. Electronic trip units use current transformers and microprocessor-based logic, offering independently adjustable long-time (Ir, tr), short-time (Isd, tsd), and instantaneous (Ii) settings. Electronic units also provide energy measurement, fault logging, and communication interfaces.

Question 3

How does SmartWire-DT integration work with NZM breakers?

Accepted Answer

A SmartWire-DT communication module clips onto the NZM breaker's auxiliary contact. The module connects to the SmartWire-DT flat cable network, which links to a gateway module on the PLC. The gateway transmits breaker status (on/off/tripped), trip cause, load current, and energy consumption to the PLC without dedicated wiring for each signal. Remote switching commands can also be sent from the PLC to the breaker's motorized operator.

Question 4

What accessories are available for NZM circuit breakers?

Accepted Answer

Key accessories include: shunt trip release for remote tripping, undervoltage release for automatic disconnection on power loss, auxiliary contacts (up to 4 NO/NC) for status signaling, motorized operator for remote switching, rotary handle for door-mounted operation, terminal extensions for rear or side connection, and arc fault detection modules. Phase barriers and terminal covers provide additional safety during maintenance.

Parameter	Value
Frame Sizes	NZM1 (125A), NZM2 (300A), NZM3 (630A), NZM4 (1600A)
Current Rating Range	20–1,600 A
Breaking Capacity (NZM2, 415V)	Up to 150 kA
Trip Unit Types	Thermal-magnetic / Electronic (NZM2-4)
Rated Voltage	Up to 690 VAC
Number of Poles	3-pole or 4-pole
Mounting	Fixed, plug-in, or withdrawable
Communication	SmartWire-DT, Modbus RTU (electronic trip unit)
Operating Temperature	-25 to +70 °C
Standards	IEC 60947-2, UL 489, CSA C22.2

Eaton NZM Molded Case Circuit Breaker

Specifications

Key Features

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Applications

Frequently Asked Questions

References & Citations