The Industrial Shock-Block (ISB) from Littelfuse is a personnel protection device designed to meet the new requirements for special-purpose ground-fault circuit interrupters (GFCIs) defined by UL 943C. ISB is the first and only permanently connected Class C and Class D GFCI on the market. Class C GFCIs are introduced to be used on systems where the line-to-line voltage is 480V or less with a trip level of 20mA, while Class D GFCI is intended to be used on 600V systems. These improvements to the standard Class A GFCI (6mA trip level used on 240V or less systems) were made to allow the use of GFCIs in industrial facilities.
ISB is also available with adjustable protection settings as an equipment ground-fault protective device (EGFPD). The EGFPD models can be set to trip at 6, 10, 20 or 30mA. This offers more flexibility, since GFCI devices are not allowed to have an adjustable trip level.
ISB (GFCI & EGFPD) is available for voltages from 208 to 600V, with a maximum full load current of 100A, and a built-in over current protection supplied by Littelfuse Class T fuses. The load can be single-phase (line-to-line) or 3-phase, however, it cannot have a neutral. The power system can either be solidly-grounded or high-resistance grounded.
Two options for enclosures are available: 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.
The ISB also monitors the ground wire (load-ground) connection between the ISB and load. This is a required feature for GFCI devices and is optional for EGFPD devices. If the connection is broken, the ISB will provide an alarm by changing the state of the alarm contacts. This monitoring circuit includes an extra wire (pilot wire) between the ISB and load (since the monitoring current is low, only a small wire is required). At the load, the pilot wire is connected to a termination device. The other end of the termination devices is connected to the load ground (typically the enclosure).
Littelfuse SB6100 Industrial Shock-Block GFCI
Littelfuse Technical Datasheets