Power-Zone 4 Arc Resistant Switchgear with ArcBlok Technology

An arc flash occurs when insulation or isolation between electrified conductors is breached or can no longer withstand the applied voltage. As employees work on or near energized conductors or circuits, movement near or contact with the equipment may cause a phase-to-ground and/or a phase-to-phase fault. Temperatures of more than 5,000 degrees Fahrenheit and a powerful explosion can be produced in an arc flash incident. OSHA has begun to enforce the NFPA 70E safety guidelines for arc flash safety. The guidelines:

• provide analysis detailing arc flash incident energy, boundary distances, and the Personal Protective Equipment (PPE);

• state that PPE must be provided;

• mandate proper worker training;

• provide procedures for safe work practices;

• state that tools for a safe work environment must be provided; and

• state that equipment be installed in accordance with the safety requirements of the National Electrical Code (NEC).

Protecting Your Personnel and Equipment from an Arc Flash

Power-Zone 4 arc resistant switchgear with MasterPacT MTZ2, 3 and NW ArcBlok technology offers patented, superior arc flash protection for operators and maintenance personnel. Power-Zone 4 arc resistant switchgear offers arc flash containment features unique to the industry in both the circuit breaker compartment and the structure.

This offer is engineered with an internal arc gas management system designed to channel dangerous arc flash energy through a pressure relief mechanism in the top of the equipment. This mechanism is comprised of either top mounted baffles (standard) or plenums (as option). The standard top mounted baffles contain roof flaps, which open to relieve pressure and allow for ejection of harmful gasses and plasma away from personnel and equipment. Optional plenums can be provided as an option to safely isolate and exhaust these gasses to a user specified location either internal or external to the facility.

• MasterPacT MTZ2, 3 or NW circuit breakers with patented ArcBlok technology (up to 5000 A)

• 60 in. (1524 mm) deep x 22 in. (559 mm) wide (smallest arc resistant footprint in the industry)

• 22 in. (559 mm), 36 in. (914 mm) section widths (30 in./762 mm section width not available)

• 60 in. (1524 mm), 72 in. (1829 mm), 80 in. (2032 mm) section depths

• Internal arc gas management system for optimized cooling

• ANSI C37.20.7 Type 2B Rating when racking into Disconnected, Test or Connected position with door closed.

• NEMA 1 enclosures

• Bus ratings up to 5000 A

• MicroLogic trip units

• Baffles (roof and floor)

• Bottom plates

• Floor dampers

• Rodent barriers

• Ground bus

• Up to 100 kAIC, 635V short circuit ratings are available

• 4 high per section breaker construction available. (Arc Resistant construction does not lower continuous current rating from standard Power-Zone 4 Switchgear ratings.)

• Insulated copper bus

• Zone selective interlocking

• High-resistance grounding

• Energy reduction maintenance switch

• Section barriers (rear, cable, and side)

• Overhead circuit breaker lifter

• Circuit breaker remote racking

• Rear covers, hinged doors

• ANSI Type 2B rated arc plenum exhaust

• Arc resistant prepared spaces

• ANSI Type 2B rated instrument compartments

• Front Door Gasketing (gasketing for side and rear covers or doors are standard)

• Arc Resistant Power-Zone 4 Switchgear is not available in NEMA Type 3R Walk-In or Front Accessible Enclosures

Power-Zone 4 arc resistant roof comprised of specific designed top covers with reinforced seams and additional hardware for additional strength and support. The roof comprises of three separate pieces: the cell roof, the bus compartment roof, which contains either a top-mounted baffle (standard) or plenum (optional), and the cable compartment roof.

Each arc resistant section comes standard with top-mounted baffles containing pressure-relief flaps, which prevent pressure build-up on front, back, and the sides of the enclosure and allow for venting of arc fault gasses out of the top of the equipment and away from personnel. The pressure relief flaps have perforated edges that are designed and calibrated to open within 5-15 milliseconds of the initiation of the arc fault and the exhausted plasma is directed up and towards the rear of the equipment. The perforated edges allow the pressure-relief flaps to remain open to prevent secondary pressure build-up. Baffles are also a critical component to the thermal ventilation system, which allow for continuous airflow and should not be obstructed. Rail-mounted, circuit breaker lifters are compatible with arc resistant baffles. Baffles ship separately and are to be installed on site. Conduit entry space is not sacrificed with arc resistant baffle assemblies.

Note for room layout: The switchgear requires a minimum switchgear base to ceiling height of 10 ft. (3 m) with no obstructions above the supplied equipment. The roof baffle must be inspected to assure it is in place and is free of damage. The temporary shipping cover must be removed to install the roof baffle before applying power to the equipment. Refer to Figure above for typical roof baffle construction. To maintain the Arc Resistant rating, the switchgear requires a minimum clearance of 3 inches from the front, rear or sides to the nearest wall or obstruction (see note below for Code required aisleways for equipment). Equipment directly coupled to the switchgear is allowed. A close coupled transformer, such as in a unit substation, is acceptable and all sections in the Power-Zone 4 Switchgear will retain their Type 2B arc resistant rating. The transformer equipment connected adjacent to the switchgear through a direct bus connection is not covered by the arc resistant rating of the switchgear. When installing the equipment, consider the aisle space required at the front and rear of the equipment, as well as space at the ends of the lineup.

As an option, UL witnessed, ANSI Type 2B rated plenums can be added to redirect and exhaust arc fault gasses and explosive energy to a secure, customer-specified location, away from equipment and personnel. Plenums can be configured to exit the top of the gear in rear or sides and modular extensions are available for custom routing up to and flush with any wall, but not through the wall. Because ventilated plenums require a complex, maintenance intensive design with dampers that can fail in the event of an arc fault, eliminating them provides users with clear benefits of reduced maintenance and increased safety. Power-Zone 4 Arc Resistant Plenums are the only non-ventilated plenums in the industry, minimizing arc fault debris, gasses, or soot from escaping into unwanted areas. Baffles are not available to be used in conjunction with plenums. Plenums are required to exit every other section to facilitate normal state heat exhaust and cannot contain bends (i.e. must be straight runs to exhaust to prevent back pressure).

Plenum Assembly Components

Plenum Elevation Drawing

NOTE: 10 ft./3 m minimum unobstructed ceiling height from base of switchgear required to install plenum and exhaust duct.

Side covers are 14 gauge steel and are designed with interlocking flanges and seams around the perimeter and in the middle of the equipment to provide additional structural integrity and improved strength. Multiple L-brackets are installed to overlap the top and side covers for added support. Insulating barriers are installed on the inside of the end covers to protect against phase-to-ground faults within the bus compartments. These insulating barriers cover the entire bus compartment end cover preventing faults from propagating from section to section. Sealing plates placed between sections also improve protection from fault propagation.

Side Cover Assembly (R) with Sealing Bracket Assembly

Due to the arc extinguishing capabilities of the patented MasterPacT circuit breakers with ArcBlok technology, front mounted arc resistant switchgear doors require no additional fasteners, hinges, or increased thickness and ultimately utilize the same doors as standard Power-Zone 4 switchgearDoors of half height have had vents removed vs. non-Arc Resistant construction to mitigate venting out of the front of the structure.*. This allows for reductions in weight and cost. Rear mounted arc resistant doors are reinforced with thicker steel (22 inches wide are 12 gauge and 36 inches wide are 10 gauge), and are structurally reinforced for additional strength.

Typical Front Door Construction

Typical Rear Door Construction

The bus compartment of each arc resistant section contains a spring-loaded floor. The floor is comprised of several compression springs, steel covered with fire retardant polypropylene insulator barrier, and a perforated base plate that allows for thermal ventilation during normal operating conditions and closes under the event of an internal arcing fault, preventing dangerous energies from escaping the bottom of the equipment. Ventilation in the floor damper assembly, allows for fully rated bus.

Arc resistant switchgear structures have been modified to include an internal baffle compartment and a repositioning of front and rear door vents to the base of the equipment for improved ventilation and convective cooling.

The internal baffle assembly employs a chamfered design which maximizes air velocity and optimizes the cooling capacity of incoming air. The baffle is designed with louvers that are covered with a chamfered bracket that also allows ground connections. All arc resistant switchgear sections contain louvered vents mounted near the base of the equipment on the rear.

The ArcBlok system is comprised of 2 primary interworking components, cluster shields and cradle barriers. The cluster shields provide isolation and protection of circuit breaker stabs in the connected, test, and disconnected positions. These cluster shields are attached to the rear of the circuit breaker and work in concert with the cradle barriers to create a labyrinth effect. This purposely designed labyrinth system helps to prevent the opportunity for faults to occur at the stabs. In the event of an arc fault, the cluster shields and cradle barriers are engineered to extinguish the arc much faster than standard switchgear.

Cluster Shields

The cradle barriers are attached to the rear of the cradle and each of the phase isolation barriers interlock with the cluster shields on the rear of the circuit breaker to complete the ArcBlok system. The cradle barrier assembly is comprised of a thermo set body and a Formex^® cover located on the top and back surfaces which make no direct contact with any grounded metal components. The Formex cover contains perforated venting slots which both allow for additional ventilation of the stab connections and transfer the arc fault away from the breaker and out the top of the gear. ArcBlok cradle barriers are provided on all circuit breakers and prepared spaces in Power-Zone 4 Arc Resistant Switchgear.

Cradle Barriers Front View	Cradle Barrier Rear View

MasterPacT Cradle with ArcBlok showing cradle barriers