Power Protection Devices
Both excessive current and excessive voltage can damage electrical and electronic equipment, and in so doing can cause serious harm—not only to the equipment but also to whatever depends on that equipment. The result can be lost production, damage to other equipment, loss of communications, or even danger to people or the environment.
Most popular devices to protect against these problems, in rank order, are fuses, circuit breakers, relays, disconnect switches, and
|Smaller trip currents are more common among respondents to Control Engineering’s first power protection Product Research survey.|
surge protectors. And they must be working, because nearly 20% of survey respondents expect to buy more over the next 12 months. To gauge trends in this product sector, Control Engineering and Reed Research Group, both part of Reed Business Information, asked subscribers about their views and preferences on power protection devices via an e-mail survey.
What users want in power protection
Selected results presented here are based on 362 full responses received in 2008 from subscribers who evaluate, specify, recommend, install, and/or purchase power protection devices. The largest number (59%) buy this equipment for in-plant requirements, 23% for resale, and 18% buy for both in-plant and OEM requirements. Overall 19% expect to buy more power protection devices; 69%, about the same; and 12% expect to buy fewer.
Product attributes ranking highest from a list of 40 were: safety features; standards, conformance markings, ratings, test compliance; current limiting; and inrush protection.
There is the temptation to increase the steady-state rating of an overcurrent protection device because of nuisance tripping due to inrush (where the protective device’s time-delay characteristics are more relevant). One respondent says, “Inrush is the most common reason for rework, and replacement of original specified power protection devices. Be aware of the necessity of time-delayed devices in certain applications.” Another added: “All power protection
|While respondents have knowledge of some of the standards related to power protection, most admit not to being experts.|
should be sized accordingly with the NEC and should be tested based on application.”
Downtime costs: half haven’t calculated
Given the ever-increasing cost of downtime, one would expect that most people would know just how much it costs when things shut down and use that information to justify power protection purchases. Yet 52% of respondents have not calculated downtime costs for machines, lines, or systems and don’t plan to do so. A further 21% have not yet, but plan to. Just 27% of respondents report having made the calculation.
Among general suggestions, Gerald Cook, a senior electrical engineer at Equinix in Foster City, CA, advised: “Application requirements must take priority. A ‘great design’ that does not meet the application requirements is really a ‘bad design.’” Michael C. Le Master, a facility manager at Tube Specialties Inc. in Tempe, AZ, says: “Do your homework; the wrong range can do almost as much damage as no protection at all.”
New power protection products
Listed below are suppliers of power protection products. For more suppliers, also visit www.controleng.com/buyersguide . For systems integrators with related expertise, go to www.controleng.com/integrators .
Space-saving circuit breaker
Cooper Bussmann Compact Circuit Protector offers 200 kA short-circuit current rating (SCCR) with Class CC fuses, using 1/3 of the space of equivalently rated circuit breakers and 2/3 the space required by a traditional fusible switch. At the same time it has a full-voltage rating of 600 V ac for more installation flexibility compared to slash-rated devices at 480/277 V ac, is horsepower rated for protecting motor circuits, and is UL98 disconnect rated for the protection of branch circuits with Class CC Fuses. Open-circuit indication is provided locally and remotely for fast troubleshooting and reduced downtime. www.cooperbussmann.com Cooper Bussmann
Ground fault relay
Littelfuse’s RCD300M2 Differential Current Relay provides highly sensitive protection while avoiding nuisance trips and unnecessary equipment shutdown that cause workers to increase trip points above sensitive levels. Features include an adjustable time delay (0-1.5s), fault indicator LEDs, and signal output to drive either a remote meter or PLC (programmable logic controller). Predictive capabilities show leakages as they develop, and ground faults can be detected before they become critical. www.littelfuse.com Littelfuse
Electronic overload relays
E3 & E3-Plus Electronic Overload Relay—Series C from Rockwell Automation offers protection, control, and preventive maintenance functions to deliver effective motor management. Units feature protective functions that can help prevent motor damage and provide advance notification when a motor’s performance parameters fall outside the boundaries of normal operation. Features include DeviceNet communications, integrated I/O termination of motor-related inputs and outputs, and preventive maintenance functions that can provide notification that motor maintenance is due based on hours of operation and/or number of starts. www.ab.com Rockwell Automation
Low-voltage circuit breaker
Series NRX low voltage power circuit breaker from Eaton Corp. provides the capabilities of a power circuit breaker in the compact size of a molded case breaker. Intended for use in switchgear and switchboards, the breaker features a cassette fold-up design that allows for part inspection, adding accessories or renewal parts without removing the cassette from the switchgear cell. It allows use of the breaker handle and cassette rails with a gloved hand, enabling electricians to wear appropriate personal protection equipment. Units are available with UL1066, UL489 and IEC ratings from 800–1600 amps and up to 65 kA short circuit interruption and 42 kA short time withstand ratings. www.eaton.com Eaton Corp.
Motor disconnect switch
Square D MD50 motor disconnect switch from Schneider Electric provides power connections in industrial facilities and prevents process interruption by cutting power to a motor if necessary, while not affecting the main circuit. IEC 60309-compliant technology makes it virtually impossible to plug in a power receptacle having different voltage and ampere ratings. A mechanical interlock forces an operator to insert a plug before power can be turned on and to turn power off before removing the plug. It is offered in 20 A, 30 A, 60 A and 100 A units, compatible with IEC 60309-2 plug configurations. It has a NEMA 4X enclosure. www.us.schneider-electric.com Schneider Electric
Wireless circuit breaker trip unit
Two new Bluetooth-enabled communication units from ABB allow a Bluetooth-enabled personal digital assistant (PDA) or personal computer to communicate with ABB PR122 and PR123 trip units from distances up to 15 feet without having to install a test cord or interface with the trip unit directly—even when the trip unit cover is sealed—to remotely gather information and make adjustments. Trip units on the company’s line of Emax low voltage power circuit breakers offer expansion slots, which allow installation of the specialized communication modules. An option for Emax circuit breakers may be added by the end user. The company also offers a self-powered Bluetooth communication unit for its line of Tmax molded case circuit breaker electronic trip systems. www.abb.com ABB
24 V dc fault isolator
The Sitop Select electronic diagnostics module from Siemens Energy & Automation provides fault detection for short circuit and current overload conditions without causing nuisance trips from high inrush loads. Typically, both fault conditions cannot be accomplished using a standard fuse or circuit breaker. The unit recognizes faults on 24 V dc circuits and selectively deactivates the faulted path while maintaining supply power to the remaining loads. Designed to be installed on the output of 24 V dc switch mode power supplies, it can be set for the overload trip from 2 A – 10 A per channel. www.sea.siemens.com Siemens Energy & Automation
Cable limiters protect networks
Ferraz Shawmut’s UL-listed CP cable limiters are designed to protect low-voltage distribution networks and service entrance cables, reducing system failures and increasing reliability. They prevent service outages by isolating damaged conductors that have experienced faults due to short circuits from splicing or insulation breakdowns. The Cable Limiters then safeguard the remaining cables to keep systems operational. Interrupting faults up to 200 kA, limiters are available in seven terminal variations. http://us.ferrazshawmut.com Ferraz Shawmut
Surge protective devices
Phoenix Contact’s ValveTrab-SQ surge protective devices (SPD) offer surge protection from 40,000 to 200,000 amps. The NEMA-style product series includes approximately 50 part numbers in three mountable designs designated by CC (control cabinet), SP (sub-panel), and SE (service entrance) identifiers. Available in single- and three-phase models, the line includes status LEDs, audible alarms, sine wave tracking filtration, and function monitoring. All units comply with UL1449 2nd Edition, 2007 requirements. www.phoenixcon.com Phoenix Contact
Monitoring and protective relays
Omron Electronics’ K8AB family of voltage, current and phase monitoring, and protective relays occupy less than half of the panel space needed for other types of monitoring relays, and simplify status monitoring with indicators to shorten troubleshooting. Available in single- and three-phase models, they offer two SPDT outputs in a 22.5 mm wide, DIN track mounting unit, and provide individual upper and lower limit outputs normally found only on larger 45-mm wide relays. Single- and three-phase units are available to monitor over- and undervoltage, sequencing, power loss, and asymmetry. Some units provide advanced warning of impending trip alarms. www.omron247.com Omron Electronics
Top 12 power protection suppliers
Control Engineering subscribers, using a list provided, identified the following vendors as leading suppliers of power protection devices. The top 12 follow in descending order by number of responses. The full report will be available in the Control Engineering Resource Center, free with registration: / .
Cooper-Bussmann , www.cooperbussmann.com
Littelfuse , www.littelfuse.com
Rockwell Automation , www.ab.com
Eaton Corp. (Cutler-Hammer), www.eaton.com
Schneider Electric (Square D, MGE), www.us.schneider-electric.com
ABB , www.abb.com
Siemens Energy & Automation , www.sea.siemens.com
Ferraz Shawmut , us.ferrazshawmut.com
GE Industrial , GE Digital Energy Phoenix Contact , www.phoenixcon.com
Omron Electronics , www.omron247.com
Thomas & Betts , www.tnb.com