Technical Overview

All Power-Zone 4 switchgear are 100% rated and are assembled and tested in an ISO 9001 facility to applicable standards including:

Power-Zone 4 switchgear has been tested for applications according to the following codes and regulations:

• IBC (International Building Code)

• ASCE 7–10

• NBCC (National Building Code of Canada)

• CBC (California Building Code)

• OSHPD (Office of Statewide Health Planning and Development)

Equipment must be anchored properly to fully comply with zone 4 installations. Additional information can be found in Bulletin No. 80298-002-05, Power-Zone 4 Low Voltage, Metal-Enclosed, Drawout Switchgear with MasterPacT Low Voltage Power Circuit Breakers. Structures are slightly modified with an additional bracket on the base of the structure which are provided for the purpose of seismic anchoring.

When Power-Zone 4 switchgear with MasterPacT circuit breakers is installed at a location greater than 6600 feet above sea level, the equipment ratings must be de-rated (see Altitude Correction Factors per ANSI C37.20.1 par. 8.1.3).

A Wye system is the most common type of three-phase distribution system for low voltage switchgear. Wye systems are either three- or four-wire distribution systems that are grounded, either in the equipment (see Four-Wire Wye Distribution (i.e. with Neutral Bus)—Solidly Grounded System - 3 phase, 4 wire), or at the transformer source (see Three-Wire Wye Distribution (i.e. without Neutral bus)—Solidly Grounded System - 3 phase, 3 wire).

Four-Wire Wye Distribution (i.e. with Neutral Bus)—Solidly Grounded System - 3 phase, 4 wire

Three-Wire Wye Distribution (i.e. without Neutral bus)—Solidly Grounded System - 3 phase, 3 wire

When the system is grounded in the equipment and the neutral phase is carried through the equipment, the system is described as a four-wire solidly grounded system with neutral connections available to supply single phase-to-neutral loads, such as lighting loads. Neutral bus is available for distributing the neutral conductor to the loads and can be rated at 50%, 100%, 150% or 200% of the phase bus ampacity depending on bus size.

When the system is grounded at the transformer source and no neutral phase is carried through the equipment, the system is described as a three-wire solidly grounded system (3W Equipment, Neutral Terminated at Source). No neutral connections are available; all loads must be three-phase (or single “phase-to-phase”) loads.

In some cases, the neutral is delivered to the service entrance where it is bonded to ground similar to the four-wire solidly grounded system but the neutral bus is not provided for neutral loads (3W Equipment, Neutral in Incoming Section only).

Delta three-wire systems are rarely used in low voltage distribution systems. Delta three-wire distribution systems can be grounded or ungrounded services. Generally, Delta systems are ungrounded. In some cases, they are grounded on the “corner” of the delta or some other point. Ungrounded Delta systems do not have a reference point or ground. Corner or Grounded B Phase Delta distribution systems do provide a reference point but require one phase to be connected to the ground.

Low voltage drawout switchgear with MasterPacT circuit breakers is designed and built to ANSI C37.20.1 and is tested for single phase-to-phase faults. They can be applied on “corner” grounded Delta distribution systems. Power-Zone 4 switchgear with MasterPacT circuit breakers is suited for corner grounded or ungrounded systems.

Three-Wire Delta Distribution—Ungrounded - 3 phase, 3 wire

Although ungrounded systems have been used for many years, they are not recommended in newly designed low voltage distribution systems. Ungrounded power systems may be unstable. High Resistance Ground Option are recommended for use in newly designed low voltage distribution systems.

Ground fault protection is available as an option on MasterPacT circuit breakers with MicroLogic 6.0X, 6.0Xi, 6.0A, 6.0P or 6.0H trip units. MasterPacT circuit breakers offer three different ground fault sensing options: residual, ground-source return and modified differential. The sensing options make it possible to match the number and location of current sensors to the application. The pickup and delay settings for ground fault are adjustable locally with the dial settings or through the key pad. The pickup and delay settings for ground fault are also adjustable remotely over a computer network on MicroLogic 6.0 and higher trip units. A neutral current sensor (NCT) must be installed in the neutral if ground fault trip is used on a three-phase, four-wire system.

All MasterPacT circuit breakers with MicroLogic 3.0X/Xi, 5.0X/Xi or 6.0X/Xi with optional Ground Fault Alarm Digital Module, 5.0P or 5.0H trip units have the ability to sense and report a ground fault alarm through the optional programmable contact module (M2C or I/O Module) or communication network. A neutral current sensor (NCT) must be installed in the neutral if ground fault alarm is used on a three-phase, four-wire system.

The pickup and delay settings for the ground fault alarm are adjustable locally through the key pad on the trip unit or remotely over a computer network.

Residual ground fault sensing systems use one current sensor for each current-carrying conductor. The trip unit vectorially sums the secondary outputs from each sensor to determine if there is a ground fault and the magnitude of the ground fault. The following diagram shows the current sensors for a three-phase, four-wire system. There is a current sensor on each phase and the neutral.

Typical Residual Ground Fault Sensing System with Phase Conductors

The sensors for the phase conductors A, B and C are inside the circuit breaker. The neutral current transformer is installed in the neutral circuit.

Ground source return ground fault sensing systems use one current sensor on the ground conductor. The current sensor measures the ground current flow. The following diagram shows the current sensor for a three-phase, four-wire system. Ground source return can also be used on three-phase, three-wire systems.

Typical Ground Source Return Sensing System with Ground Fault Interface Module and Current Sensor

Ground-source return sensing systems require the use of the optional ground fault interface module and a sensor installed in the ground circuit.

The current sensor and ground fault interface module must be wired per the installation and wiring instructions included with the ground fault interface module.

A modified differential ground fault system (MDGF) is used for multiple sourced systems. Normal residual and ground-source return systems will not correctly sum all of the circulating currents caused by the multiple neutral paths and multiple grounds. The following diagram shows a typical main-tie-main system. Each source transformer is grounded, and the service entrance neutral is bonded to ground. Multiple neutral paths allow neutral current to circulate and return to the supplying transformer by several different paths. The ground fault system must be capable of correctly summing these circulating currents.

Typical Modified Differential Ground Fault System with Ground Fault Interface Modules

The modified differential ground fault sensing system requires the use of ground fault interface modules and current sensors installed in all normal current-carrying conductors.

The current sensors and ground fault interface modules must be wired in parallel and the polarity of the current sensors must be maintained per the installation and wiring instructions included with the ground fault interface module.

The resistor unit consists of a group of industrial resistors arranged to provide the proper resistance and capacity to dissipate heat under all operating conditions. The resistor unit may be mounted in an internal compartment in the low voltage equipment. When mounted in the low voltage equipment, the compartment is adequately ventilated to dissipate the heat developed during ground fault conditions. If the desired compartment cannot be sufficiently ventilated, or if one is not available, the equipment resistor unit is mounted on top of the equipment or in some remote location. An example of a ventilated resistor enclosure is shown below in Typical Resistor Assembly

Typical Resistor Assembly

Door Component Locations below illustrates the door-mounted components of a typical high resistance ground unit.

Door Component Locations

Each main circuit breaker connects to a utility source or one main circuit breaker connects to a utility source and the other man circuit breaker connects to a generator source. When the normal source becomes unavailable, the system transfers to the alternate. If the system comes equipped with a preferred source selector option, the system reverts to the preferred source automatically once it is available. Without the selector, automatic retransfer does not occur.

Optional listing to UL 1008 for both closed and open transition transfer schemes is available. When an open transition UL 1008 listed transfer scheme is specified, a mechanical interlocking cable is provided between the two main circuit breakers (main-main or main-generator) to assure that at least one circuit breaker is always open. This way, one circuit breaker is open prior to closing the other main.

Main-Main (or Generator) Circuit Breaker Configuration

The PLC based, breaker-based automatic transfer design from Schneider Electric are designed to meet Underwriters Laboratories (UL) 1008 and to be applied on National Electrical Code^® (NEC^®) 700, Emergency Systems. They are also applicable to NEC 701, Legally-Required Standby Systems and NEC 702, Optional Standby Systems.

Both main circuit breakers, connected to a utility source, are connected together by means of a normally open tie circuit breaker.

Main-Tie-Main (or Generator) Circuit Breaker Configuration

Layout Arrangement for Main-Tie-Main Power-Zone 4 Lineup Automatic Transfer PLC Solution

Full Sequences of Operation for these pre-engineered PLC Automatic transfer Systems can be obtained by contacting Schneider Electric.

The diagram is shown with circuits de-energized, all devices open, connected and charged and relays in normal position.

Power For a three-pole MasterPacT MTZ circuit breaker in a power system with neutral distributed, the neutral must be connected to the Vn terminal of the MicroLogic X control unit and the ENVT configured to "Yes" to maintain the quality of power measurement.*	Control Unit

Remote Operation It is possibe to add a second MX/MX diag&com or an MN/MN diag coil. *

Indication Contacts	Cradle Contacts

Terminal Block Marking

Lineup contains only one(1) incoming main from utility, transformer, or generator. The purpose of the single main is to disconnect all incoming conductors from the source.

• Source may be connected to the lineup via Cable, Close Coupled to Transformer or Busway.

• No tie breakers are required in Single Main configuration.

Main can be top or bottom incoming. The Main can be on the left or right side of the lineup. All feeders on left located main can only be located to the right of the main. All feeders on right located main can only be located to the left of the main.

Lineup contains two (2) incoming mains from utility or upstream transformer. The purpose of the Main-Tie-Main configuration is to allow the feeders to be supplied power from 2 sources with a tie breaker disconnect between Bus “A” and Bus “B”. The normally open tie isolates the 2 buses both electrically (when open) and physically with barriers. In case one utility main is unavailable the feeders can all be fed from the remaining available source by closing the tie. The opening and closing of the mains/tie for various operating conditions are controlled by automatic source controllers or key interlocking.

• Sources may be connected to the lineup via Cable, Close Coupled to Transformer or Busway

Mains can be the same incoming direction (both top, both bottom) or be top incoming on one and bottom incoming on the other. End Fed Main-Tie-Main will have the main disconnects physically and electrically located at the left and right ends of the lineup. All feeders will be in between the mains and separated by the tie as shown in the figure above.

When both mains have incoming direction the same the tie breaker must have an additional bus transition section on its right side to properly locate the horizontal cross bus to the top or bottom.

In the case of the 2 mains having different incoming directions the addition of a bus transition is not necessary.

Multiple Tie Breakers are available by contacting the Schneider Electric factory.

Lineup contains one (1) incoming main from utility or upstream transformer AND one (1) incoming main disconnect for backup generator source. The purpose of the Main-Tie-Generator configuration is to allow all feeders in the lineup to be supplied power from Main 1 (normally closed) and the Tie breaker (normally closed). The Generator and its Main 2 (normally open) are available as a backup source in case the Main 1 source is unavailable. The Tie breaker opens during a transfer to the generator. The opening and closing of the mains/tie for various operating conditions are controlled by automatic source controllers or key interlocking.

• Sources may be connected to the lineup via Cable, Close Coupled to Transformer or Busway (

Mains can be the same incoming direction (both top, both bottom) or be top incoming on one and bottom incoming on the other. End Fed Main-Tie-Generator will have the main disconnects physically and electrically located at the left and right ends of the lineup and cannot be moved. The Generator Main can be selected to be on the right or left end of the lineup. All feeders will be in between the mains and separated by the tie as shown in the figure above.

When both mains have incoming direction the same the tie breaker must have an additional bus transition section on its right side to properly locate the horizontal cross bus to the top or bottom.

In the case of the 2 mains having different incoming directions the addition of a bus transition is not necessary.

End Fed Main-Tie-Generator allows for a maximum two (2) Main Breakers. When more than 2 incoming mains with options are required contact Schneider Electric factory.

Multiple Tie Breakers are available by contacting the Schneider Electric factory.

Lineup contains one (1) incoming main from utility or upstream transformer AND one (1) incoming main disconnect for backup generator source. The purpose of the Main-Generator configuration is to allow all feeders in the lineup to be supplied power from Main 1 (normally closed). The Generator and its Main 2 (normally open) are available as a backup source in case the Main 1 source is unavailable or there is a source 1 power failure. The opening and closing of the mains for various operating conditions are controlled by automatic source controllers or key interlocking.

• Sources may be connected to the lineup via Cable, Close Coupled to Transformer or Busway.

Mains can be the same incoming direction (both top, both bottom) or be top incoming on one and bottom incoming on the other. End Fed Main-Generator will have the main disconnects physically and electrically located at the left and right ends of the lineup and cannot be moved. The Generator Main can be selected to be on the right or left end of the lineup. All feeders will be in between the mains as shown in the figure above.

In the case of the 2 mains having same incoming directions the addition of a bus transition is not necessary.

End Fed Main-Generator allows for a maximum two (2) Main Breakers. When more than 2 incoming mains with options are required contact Schneider Electric factory.

Lineup contains two (2) incoming mains from utility or upstream transformer. The purpose of the Main-Main configuration is to allow all feeders in the lineup to be supplied power from Main 1 (normally closed). Main 2 (normally open) is available as a backup source in case the Main 1 source is unavailable or there is a source 1 power failure. The opening and closing of the mains for various operating conditions are controlled by automatic source controllers or key interlocking.

• Sources may be connected to the lineup via Cable, Close Coupled to Transformer or Busway.

Mains can be the same incoming direction (both top, both bottom) or be top incoming on one and bottom incoming on the other. End Fed Main-Main will have the main disconnects physically and electrically located at the left and right ends of the lineup and cannot be moved. All feeders will be in between the mains as shown in the figure above.

In the case of the 2 mains having same incoming directions the addition of a bus transition is not necessary.

If more than 2 incoming mains are required contact Schneider Electric factory.

Similar in features to the End Fed Main-Tie-Main except Center Fed Main-Tie-Main will have the main disconnects physically and electrically located in between all feeders. All feeders will be located to the right or left of the mains and separated by the tie as shown in the figure above. Feeders cannot be placed in between the mains as this would not be a Center Fed topology.

When both mains have incoming direction the same the tie breaker must have an additional bus transition section on its right side to properly locate the horizontal cross bus to the top or bottom. In the case of Center Fed Main-Tie-Main.

In the case of the 2 mains having different incoming directions the addition of a bus transition is not necessary.

Multiple Tie Breakers are available by contacting the Schneider Electric factory.

Similar in features to the End Fed Main-Tie-Generator except Center Fed Main-Tie-Generator will have the main disconnects physically and electrically located in between all feeders. The Generator Main can be selected to be on the right or left side of the tie in the lineup. All feeders will be located to the right or left of the mains and separated by the tie as shown in the figure above. Feeders cannot be placed in between the mains as this would not be a Center Fed topology.

When both mains have incoming direction the same the tie breaker must have an additional bus transition section on its right side to properly locate the horizontal cross bus to the top or bottom. Feeders cannot be placed in this additional bus transition section in the case of Center Fed Main-Tie-Main.

In the case of the 2 mains having different incoming directions the addition of a bus transition is not necessary.

If more than one Tie Breaker or multiple Generator Breakers are required contact the Schneider Electric factory.

Similar in features to the End Fed Main-Generator except Center Fed Main-Generator will have the main disconnects physically and electrically located in between all feeders. The Generator Main can be selected to be on the right or left side of the utility main. All feeders will be located to the right or left of the mains as shown in the figure above. Feeders cannot be placed in between the mains as this would not be a Center Fed topology.

In the case of the 2 mains having same incoming directions the addition of a bus transition is not necessary.

If more multiple Generator Breakers are required contact the Schneider Electric factory.

Similar in features to the End Fed Main-Main except Center Fed Main-Main will have the main disconnects physically and electrically located in between all feeders. All feeders will be located to the right or left of the mains as shown in the figure above. Feeders cannot be placed in between the mains as this would not be a Center Fed topology.

In the case of the 2 mains having same incoming directions the addition of a bus transition is not necessary.

If more than 2 incoming mains are required contact Schneider Electric factory.

Lineup contains two (2) incoming mains from utility or upstream transformer AND two (2) tie breakers. The purpose of the Main-Tie-Tie-Main configuration is to allow the feeders to be supplied power from 2 sources with two (2) tie breaker disconnects between Bus “A” and Bus “B”. In the normal state one tie is closed and one is open. The two (2) ties configuration provides additional maintenance advantages vs. one (1) tie configuration. For example, maintenance can be performed on one of the ties creating a state where it is fully de-energized on both sides by opening the other tie (assuming the ties are in separate sections and the main feeding the corresponding tie is open). Additionally, for load flexibility feeders can be added between the two (2) tie breakers to allow either bus to feed loads between the ties in case one source is unavailable. Both ties can be opened to de-energize the loads between them.

Much like the single tie configuration, in case one utility main is unavailable the feeders can all be fed from the remaining available source by closing both ties. The opening and closing of the mains/ties for various operating conditions are controlled by automatic source controllers or key interlocking.

Sources may be connected to the lineup via Cable, Close Coupled to Transformer or Busway.