General Information

The MasterPact™ NT/NW Universal Power Circuit Breaker is designed and tested to meet IEC 609472 and 60947-3 Standards and Certified to ABS-NVR^® (American Bureau of Shipping–Navel Vessel Rules). These circuit breakers are specifically designed and tested for shipboard use to protect electrical systems from damage caused by overloads, short circuits and equipment ground faults. All MasterPact circuit breakers are designed to open and close a circuit manually, and to open the circuit automatically at a predetermined overcurrent setting. MasterPact circuit breakers can also:

• Enhance coordination by their adjustability.

• Provide integral ground-fault protection for equipment.

• Provide high interrupting ratings and withstand ratings.

• Provide communications.

• Provide power monitoring.

• Provide protective relaying functions.

• Provide zone-selective interlocking (ZSI) which can reduce damage in the event of a fault.

MasterPact circuit breakers are manufactured and tested in accordance with the following standards:

MasterPact circuit breakers are available in Square D™ or Schneider Electric™ brands.

High Ampere Interrupting Rating (AIR)

MasterPact NW circuit breakers have an interrupting rating of 150 kA at 440 Vac without fuses.

High Short-Time Current Rating

MasterPact NW circuit breakers have exceptional short-time ratings—up to 100 kA.

100% Rated Circuit Breaker

MasterPact circuit breakers are designed for continuous operation at 100% of their current rating.

Reverse Fed Circuit Breaker

MasterPact circuit breakers can be fed either from the top of the circuit breaker or from the bottom.

Two-Step Stored Energy Mechanism

MasterPact circuit breakers are operated via a stored-energy mechanism which can be charged manually or by a motor. The closing time is less than five cycles. Closing and opening operations can be initiated by remote control or by push buttons on the circuit breaker front cover. An O–C–O cycle is possible without recharging.

Drawout or Fixed Mount, 3-Pole (3P) or 4-Pole (4P) Construction

MasterPact circuit breakers are available in drawout or fixed mounts, with either three-pole or four-pole construction.

Field-installable Trip Units, Sensor Plugs and Accessories

Trip units, sensor plugs and most accessories are field installable with only the aid of a screwdriver and without adjusting the circuit breaker. The uniform design of the circuit breaker line allows most accessories to be common for the whole line.

Reinforced Insulation

Two insulation barriers separate the circuit breaker front from the current path.

Isolation Function by Positive Indication of Contact Status

The mechanical indicator is truly representative of the status of all the main contacts.

Segregated Compartment

Once the accessory cover has been removed to provide access to the accessory compartment, the main contacts remain fully isolated. Furthermore, interphase partitioning allows full insulation between each pole even if the accessory cover has been removed.

Front Connection of Secondary Circuits

All accessory terminals (ring terminals are available as an option) are located on a connecting block which is accessible from the front in the connected, test and disconnected positions. This is particularly useful for field inspection and modification.

Anti-Pumping Feature

All MasterPact NT and NW circuit breakers are designed with an anti-pumping feature that causes an opening order to always takes priority over a closing order. Specifically, if opening and closing orders occur simultaneously, the charged mechanism discharges without any movement of the main contacts keeping the circuit breaker in the open (OFF) position.

In the event that opening and closing orders are simultaneously maintained, the standard mechanism provides an anti-pumping function which continues to keep the main contacts in the open position.

In addition, after fault tripping or opening the circuit breaker intentionally (using the manual or electrical controls and with the closing coil continuously energized) the circuit breaker cannot be closed until the power supply to the closing coil is discontinued and then reactivated.

Disconnection Through the Front Door

The racking handle and racking mechanism are accessible through the front door cutout. Disconnecting the circuit breaker is possible without opening the door and exposing live parts.

Drawout Mechanism

The drawout assembly mechanism allows the circuit breaker to be racked in four positions (connected, test, disconnected, or withdrawn), as shown in the figure below.

Reduced Maintenance

Under normal operating conditions, the circuit breaker does not require maintenance. However, if maintenance or inspection is necessary, the arc chambers are removable to allow visual inspection of the contacts and wear indicator groove (see Contact Wear Indicators for how wear is indicated). The operation counter can also indicate when inspections and possible maintenance should be done.

MasterPact circuit breakers can operate under the following temperature conditions:

The electrical and mechanical characteristics are stipulated for an ambient temperature between -13°F (25°C) and 158°F (70°C). Mechanical closing of the circuit breaker (by pushbutton) is possible down to -31°F (-35°C).

It is recommended that the equipment be cooled or heated to the proper operating temperature and kept free of excessive vibration and dust. Operation at temperatures above 122°F (50°C) may require derating or overbussing the circuit breaker. See the appropriate instruction bulletin and Temperature Correction Factors for additional information.

MasterPact circuit breakers have been tested to meet ABS-NVR Standards.

MasterPact circuit breakers meet IEC 68-2-6 Standards for vibration.

• 2 to 13.2 Hz and amplitude 0.039 in. (1 mm)

• 13.2 to 100 Hz constant acceleration 0.024 oz. (0.7 g.)

The materials used in MasterPact NT and NW circuit breakers will not support the growth of fungus and mold.

MasterPact circuit breakers have been tested to the following:

• IEC 68-2-30 - Damp heat (temperature +55°C and relative humidity of 95%)

• IEC 68-2-52 level 2 - salt mist