Protection Inside the Box

The ultimate circuit protection is normally an electromechanical circuit breaker. However, electronic techniques continue to provide protection inside enclosures, closer to where fault conditions could occur. “Communication systems such as PROFIBUS are a critical part of a customer’s operation, and downtime is unacceptable,” said Ed Doherty, product marketing manager for Phoenix Contact’s TRABTECH surge product line. To reduce downtime, designers look to suppliers for approaches to take the burden of the circuit breaker and provide protection techniques inside the expensive electronics equipment. Three non-electromechanical solutions include surge suppressors, over-current/over-voltage (OC/OV) protection devices and gas plasma arresters.

OC/OV PROTECTION DEVICE

Designed to help prevent damage to telephony communications equipment, Raychem Circuit Protection’s 2Pro device series offers integrated overcurrent/overvoltage circuit protection technology. The small device uses Raychem’s PolySwitch Polymeric Positive Temperature Coefficient Resistor (PPTC) overcurrent technology with a Metal Oxide Varistor (MOV) to help prevent power surge damage resulting from lightning and Electrostatic Discharge (ESD) with AC lines. The 2Pro devices are available in tape and reel packaging and compatible with industry standard installation procedures. The unit has a hold current of greater than 120 mA and the voltage clamp at 1 mA is approximately 270V. The protection device helps equipment comply with surge tests per TIA-968-A, IEC 60950 and ITU-T K.20/K.21. The unit targets applications in Voice over Internet Protocol (VoIP) gateways, cordless phones, security systems, Integrated Services Digital Network (ISDN) linecards and Main Distribution Frame (MDF) modules. Get more information on Raychem Circuit Protection’s 2Pro device.

GAS PLASMA ARRESTOR

Manufactured to protect highly exposed external telecommunications equipment, Littelfuse Inc.’s SL1411A series is a two-terminal Gas Discharge Tube (GDT) rated at 10 kA/10A ac that combines a high surge rating with low-voltage clamping. Using newly enhanced materials, the arresters can handle surges up to 55 kA and reduces the transient to the lowest possible level thus reducing service maintenance. With an ultra-low capacitance of typically 1 pF or less, the units can respond to fast-rising transients in the 100 to 1000 V/µSec range that can occur in induced lightning disturbances. The unit’s minimum dc breakover voltage is 184V, maximum voltage is 275V and the maximum dynamic breakover voltage is 450V. The device maintains a stable breakover voltage even with repetitive 10 kA pulsing, which helps reduce damage to outside plant applications and reduces the stress on secondary protection devices. Get more information on Littelfuse Inc.’s SL1411A series Gas Plasma Arrestor.

SURGE SUPPRESSORS

Designed for PROFIBUS-DP applications, Phoenix Contact’s D-UFB-PB surge protection is integrated into the fieldbus connector. In PROFIBUS applications, damaging surges can travel on signal lines and the integrated surge protection eliminates the need for additional protective devices and saves space. The PROFIBUS cable connects directly to the surge protector and can be used with the latest generation Siemens PLCs. Measuring 35 mm in height, the small D-UFB-PB protector can handle data rates up to 12 Mbits/sec. Response time, tA, for core to core or core to ground is less than 500 ns. The arrester’s rated voltage is 5.2V with the nominal discharge surge current, In (8/20 µSec), of 350A. The nine-position D-SUB plug uses color-coded screw clamp terminal blocks for easy installation. A slide switch at the connector easily activates the termination resistor saving installation and start-up time. Get more information on Phoenix Contact’s D-UFB-PB surge protector.