monitor the grounding conductor and it shuts off power when
the integrity of that conductor is compromised. Therefore,
industrial GFCIs will reduce the cost associated with the
assured equipment grounding conductor program and will
make the compliance with NEC and OSHA requirements
mentioned above much easier.
VII. APPLICATION EXAMPLE
A pulp and paper plant in Wisconsin uses a 480 V re-reeler
wind-up cart to transfer the spool of paper after it has gone
through the re-reeler to a truck trailer loading station. The
power source comes up through the floor by a cord reel
system. The cable lays and travels in one of the cart’s tracks,
therefore there is a potential for the cable to get damaged. In
this case, the cart and the cart track could be energized to
480 V; creating a high risk of an electric shock if anyone
comes in contact with the cart or the cart track. The re-reeler
wind-up cart is shown in Fig. 8.
Fig. 8 The re-reeler wind-up cart
The aforementioned hazard troubled the plant management
but due to the inexistence of a 480 V GFCI, there was no
viable solution to the problem. Since UL listed industrial
GFCIs are now available, there is a potential solution that can
minimize the risk of injuries from electric shocks.
Plant management acknowledged the potential of industrial
GFCIs and decided to install a 480 V Class C GFCI. The unit
was installed near the MCC in the plant basement. Fig. 9
shows the connection diagram of the unit, and the actual
GFCI installed is shown in Fig. 10.
Fig. 9 Connection diagram of the industrial GFCI
Fig. 10 Class C GFCI installed at the plant
Testing is currently underway to make sure that there is no
nuisance tripping. After finishing all required tests, the
expectation is to install another 480 V GFCI on the unwind
cart which has a similar power cord design. Management is
also considering different 480 V applications in the mill that
could benefit from the value of personnel protection provided
by industrial GFCIs.
VIII. CONCLUSIONS
Due to the UL 943C allowances for the design and setting
beyond the 6 mA trip level, false trips could potentially be
eliminated. Ground conductor integrity monitoring of industrial
GFCIs lessens the cost associated with testing requirements
of the assured equipment grounding conductor program. The
continuous monitoring for the electrical shock hazard afforded
by the GFCI helps to ensure a high degree of personnel
safety. For these reasons GFCIs, for use at voltage levels
other than 125 V, are a cost effective method to help assure a
high level of personnel safety from an electric shock hazard.