Littelfuse Industrial Shock Block

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Littelfuse’s Industrial Shock Block (ISB) is designed to meet the requirements for special-purpose GFCIs defined by UL 943C.

Class C GFCIs are intended to be used on three-phase systems where the line-to-line voltage is 480 V or less with a trip level of 20 mA, while Class D GFCIs are intended to be used on 600 V systems. The ISB is available as a Class A GFCI for construction sites with wet areas to meet NEC 210.8(B).

  • Equipment ground-fault protective device: The ISB is also available with adjustable protection settings as an EGFPD. The EGFPD models can be set to trip at 6 mA or from 10-100 mA in increments of 10 mA.
  • Rating and models: The ISB is available for three-phase voltages from 208 to 600 V with a maximum full load current of 100 A. The power system can be either solidly or high-resistance grounded. UL-recognized open-chassis models are available for installation in existing electrical enclosures and UL-listed enclosed models include a NEMA-4X enclosure for stand-alone installations.

  • Ground wire (load-ground) monitor: The ISB also monitors the ground wire connection between the ISB and load.

  • UL 943 inverse time trip curve: Detects and interrupts to protect people and reduce the probability of nuisance tripping

  • Minimum trip time < 20 msec: Reduces the risk of ventricular fibrillation for leakage current of 250 mA and above

  • Selectable trip levels (EGFPD): Provides extra safety when able to operate with a setting below 20 mA (GFCI), and the settings above 20 mA can reduce nuisance tripping

  • Undervoltage, brownout, chatter detection: Ensures proper operation and prolongs the internal contactor lifetime

  • Operator interface: Shows unit status, alarm types, percentage of leakage current, and allows for test and reset capabilities


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