The Fundamentals: Five Practical Considerations When Choosing Arc-Resistant MCC'S

Kathy | January 1, 2007


Arc-resistant motor control centers (MCCs) help protect employees from dangerous arc flashes while reducing the risks of the high costs related to these incidents. Before you invest, make sure you take the following equipment and installation aspects into consideration. They definitely can impact your safety, your maintenance and your costs.

  1. Arc-resistant MCCs should be tested to relevant standards such as:
    • IEEE C37.20.7.
    • IEC 62271-200 (Annex AA).
    • EEMAC G14-1.
  2. Ask to see the Certified Test Report to corroborate the results that are claimed by the manufacturer. Passing IEEE C37.20.7 testing means that if an arc flash occurs:
    • Doors and covers do not open.
    • No parts are ejected from the equipment.
    • The arc does not burn any holes in the exterior of the tested structure.
    • Cotton indicators (150 g/m2), which represent typical industrial work suits,must not ignite.
    • The grounding connections remain effective.
  3. To ensure equivalent evaluation of arc-resistant motor control equipment, be aware of the test condtions used by each vendor, including the voltage, arc current and arc duration, whether a plenum was used and the number of structures tested simultaneously (tests performed on a single structure are more onerous, compared to testing of multiple structures).
  4. Know the accessibility level of the equipment.Under IEEE standards, Type 1 Accessibility offers enhanced protection at the front of the MCC; Type 2 steps up the coverage to the front, rear and sides.
  5. Also consider installation requirements when purchasing arc-resistant equipment.
    • Where will it be installed?
    • Is there overhead clearance and accessibility for external exhaust?
    • Does the area have existing cable, conduit or HVAC ducting?

Arc-resistant equipment can be a vital part of your safety program.Making the right choice requires knowing what to look for.

Redirecting Dangerous Arc Flash Energy

0107_fundamentals_arc_img1Rockwell Automation offers Allen-Bradley® CENTERLINE® ArcShieldTM medium and low-voltage arc-resistant motor controllers for rugged process control that are compliant to the IEEE C37.20.7 standard, Type 2 protection. The medium-voltage equipment maintains this level of protection, even when the low-voltage door is open during simple maintenance procedures. During an arc flash, the ArcShield controller redirects arc flash energy out the top of the unit and away from personnel.ArcShield is part of Rockwell Automation’s Intelligent Motor Control solutions that provide solutions like remote monitoring and real-time troubleshooting without the need to open unit doors, using IntelliCENTER software.

Rockwell Automation
Milwaukee, WI

Pre-Verify Electrical Isolation With “No-Touch”Voltage Portal

Installed on an electrical panel, the Chek- Volt™ interface, from Grace Engineered Products, allows maintenance personnel to use a non-contact voltage detector “pen” to check line voltage before and after they open the main disconnect. The ability to pre-verify electrical isolation before opening a panel puts an additional safety measure between electricians and hazardous voltage. 0107_fundamentals_arc_img2The ChekVolt simply extends the line voltage from the main disconnect (or other voltage source) through a wire into an encapsulated non-metallic assembly fastened to the enclosure exterior. The single point ChekVolt R-1A has 6’ leads, mounts into a 0.50” (13mm) drilled hole, and can be ordered with a full line of bright yellow nameplates. Non-contact voltage detectors typically operate from 50/90-1000VAC, which allow users to apply ChekVolt to single or 3-phase AC power systems. Optional bright yellow nameplates remind personnel to pre-verify every voltage point before accessing the panel interior. Nameplates offered include various power system graphics or generic single-phase/3-phase nameplates. ChekVolt is a UL listed 600V device and rated for use in NEMA 4/4X/12 environment.

Grace Engineered Products, Inc.
Davenport, IA

New Enclosed Disconnect Switches

0107_fundamentals_arc_img3Ferraz Shawmut’s new line of Enclosed Disconnect Switches is designed to meet plant maintenance operators’ requirements for compact and durable individual disconnecting means.Available in fusible and nonfusible versions, they provide safety, high performance for many environments, operational convenience and easy installation. According to their manufacturer, the Enclosed Non-Fused Disconnect Switches are often employed as motor disconnect switches to comply with NEC Article 430 for ‘line of sight’ applications. Other applications include using the Fusible Enclosed Disconnects for panels with no incoming disconnection provision, and employing them to help mitigate the risk of arc flash hazards.


Ferraz Shawmut
Newburyport, MA

Electrical Safety And Compliance Training Material

A complete collection of advanced electrical training publications and e-training modules are now available from authorized Cooper Bussmann distributors, or online, to help reduce downtime, improve workplace safety and address code compliance issues. Developed for contractors, industrials, OEMs, inspectors and educators, the materials provide a training resource to help electrical industry workers comply with the latest NEC® and industry standards; select and apply overcurrent protective devices; determine fault current levels; and analyze and improve electrical system performance and stability.

Cooper Bussmann also offers an Express Member Service that provides a range of additional services: unlimited access to all technical training downloads; a free copy of the company’s innovative Selecting Protective Devices; a free Specification Grade Protection DVD; and exclusive memberonly offers and discounts.

Cooper Bussmann
St. Louis, MO

Arc Flash Calculation Software Upgrade

Advantica has added a valuable arc flash calculation tool to its SynerGEE® Electric software to help engineers develop strategies to minimize burn injuries resulting from arc flash incidents. Housed in SynerGEE’s robust Protection Coordination module, the new arc flashover analysis is based upon the IEEE 1584-2002 standard and fully integrated into the core electric software like other SynerGEE analyses.Advantica’s arc flash analysis determines the amount of potential current flow through a point in a distribution or transmission system and the time required for the nearest upstream protective device to function in the event of a fault.

Mechanicsburg, PA

Power Distribution Analysis System Helps Calculate Arc Flash Potential

ZMeters’ ZM100 Distribution Analysis System utilizes time-synchronized, multipoint measurement and correlation techniques to characterize the0107_fundamentals_arc_img5 impedance of distribution systems in industrial, commercial or medical facilities. According to the manufacturer, since its introduction last year, the product’s unique, two-meter impedance measuring system also has been found to be well suited to making empirical measurements of the impedances required to perform arc flash potential calculations. The ZM100 system consists of two or more ZM100 Distribution Analyzers, each connected to a salient point in the facility’s electrical distribution system. Each of these devices is equipped to make time-synchronized and highly accurate measurements of voltages and currents for all phases and neutral.Measurements are made and data are gathered over a time period that characterizes the range of operating conditions that typically exist in the facility. The data is then communicated to a PC using Bluetooth wireless communications. The ZM100 Windows-based software performs a range of calculations and cor r e l a t i o n s resulting in a characterization of the distribution system’s i m p e d a n c e (both at line frequency and harmonics). Using the resultant characterization, distribution impedance abnormalities can be readily identified and necessary corrective measures can be prescribed.

Z Meters, Inc.
Baltimore, MD

Playing It Safe With Wireless

0107_fundamentals_arc_img6ProSoft Technology’s inRAx Wireless Ethernet/IP Communication Module (MVI56-WA-EIP) acts as a wireless bridge, enabling remote connectivity between a ControlLogix processor and 802.11 wireless devices including: PCs, Laptops, radio modems such as the RadioLinx Industria HotspotTM and other MVI56-WA-EIP modules. Keeping users safe from arc flash incidents is just one of this product’s many benefits.With approximately 10 arc flash explosions in the U.S. each day and nearly five severe burn victims associated with each explosion, the costs saved by avoiding these incidents can be substantial. The MVI56-WA-EIP allows access to needed data without staff having to enter into mandated flash boundary zones and without them having to touch processors.

ProSoft Technology
Bakersfield, CA






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