Industrial GFCIs help meet OSHA grounding requirements
How can workers be protected against electric shock when working with temporary wiring? While the safety provisions necessary for the normal wiring system in a plant are widely known, the same cannot be said for the temporary wiring used during scheduled shutdown maintenance or, as OSHA puts it, "construction-like activities including certain maintenance, remodeling, or repair activities involving buildings, structures, or equipment." OSHA cites, as examples, minor building repairs using temporary wiring and water-blasting (hydro-cleaning) of heat-exchanger tubing.
OSHA requires that these and similar activities incorporate ground-fault circuit interrupters (GFCIs) per 29 CFR Part 1910 Subpart S. Usually, this is done by using a portable distribution board (spider box) or portable power outlet with a GFCI inside it, but there has been a problem when the voltages involved exceed 125 V, single-phase. Until recently, there were no GFCIs approved for higher voltages, and for these situations OSHA added the requirement 1910.304(b)(3)(ii)(C) for an assured equipment grounding conductor program.
This requirement says, in part, "In industrial establishments only, where conditions of maintenance and supervision ensure that only qualified personnel are involved, an assured equipment conductor program … shall be permitted for only those receptacle outlets used to supply equipment that would create a greater hazard if power were interrupted or having a design that is not compatible with GFCI protection." This same requirement is in the NFPA 70: National Electrical Code (NEC) in Article 590.6(B)(2).
The requirements for such an assured equipment grounding conductor program are strict. They include a written description of the program, including the specific procedures adopted by the employer; the designation of a competent person to implement it; a daily visual inspection of each cord set, attachment cap, plug, and receptacle of cord sets and any equipment connected by cord and plug, except cord sets and receptacles that are fixed and not exposed to damage; and electrical tests for continuity and correct attachment of the equipment grounding conductor. These tests must be done before first use; before equipment is returned to service following any repairs; before equipment is used after any incident that can be reasonably suspected to have caused damage (for example, when a cord set is run over); and at intervals not to exceed 3 months-with the exception being cord sets and receptacles that are fixed and not exposed to damage must be tested at intervals not exceeding 6 months. Results of all such tests must be recorded and kept available for inspection.
What’s more, this work must be done by a qualified worker (as defined by OHSA 1926.32(f) and 1910.399) who demonstrates skills and knowledge related to the electrical equipment and has received safety training to recognize and avoid the hazards involved.
This is burdensome, time-consuming, and expensive—especially if many cords are involved. But GFCI technology has advanced since the standard was written, and a close look shows that the assured equipment grounding conductor program is required only in cases where a suitable GFCI is not available—which leads to a potential solution to the problem.
Solution to the problem
While there were no readily available GFCIs for voltages greater than 125 VAC when the OSHA requirements were written in 2007, there are now industrial-voltage GFCIs on the market that both provide shock protection and continuously monitor the integrity of equipment grounding circuits, shutting off the power if there is a problem (fig. 2). UL calls them special-purpose GFCIs (SPGFCIs) and divides them into three classes, per UL 943C.
- Class C covers GFCIs for use in circuits with no conductor over 300 VAC to ground where reliable equipment grounding or double insulation is provided. ·
- Class D covers GFCIs intended to be used in circuits with one or more conductors over 300 V to ground, and with specially sized, reliable grounding to provide a low impedance path so that the voltage across the body during a fault does not exceed 150 V.
- Class E covers GFCIs for use in circuits with one or more conductors over 300 V to ground but with conventional equipment grounding provided for the protected equipment in the system or double insulation.
These units can eliminate the need for periodic inspection and testing required in the assured equipment grounding conductor program while providing personnel protection at the same time, which can mean great savings in time and labor.
There are situations in which the 20 mA trip current of a SPGFCI is too low. In these cases, equipment ground-fault protection devices (EGFPDs) can be used. EGFPDs are similar to GFCIs but have trip levels adjustable up to 100 mA, thus they cannot be classified as GFCIs. They are intended mainly for protection of equipment, rather than people. But they still provide all the ground circuit monitoring of a SPGFCI.
Examples from the field
One major oil company has begun experimenting with SPGFCIs by installing a Littelfuse Shock Block SPGFCI in a mobile NEMA 3R enclosure that feeds 480 V, 3-phase power to a portable sump pump. This has eliminated the need to conduct an assured equipment grounding conductor program on the wiring for this piece of equipment, saving several hours of labor during each shutdown and freeing up qualified workers for other tasks.
A typical medium- to large-size refinery may devote 1 to 2 man-years on an assured equipment grounding conductor program. With a comparatively small investment in grounding devices, refineries and other plants having maintenance shutdowns may achieve considerable labor savings.
Managers will need to calculate the payback period by considering the number of temporary receptacles used with loads above 125 V, the number of SPGFIs needed to protect those receptacles, and the labor cost of inspections and documentation. SPGFIs may be reused for each shutdown and relocated if needed.
At this refinery, managers noted an additional benefit: compliance is automatic and does not depend on human behavior.
Two other loads were connected to a distribution unit, and immediately proved the value of a GFCI. The first was an arc welder; as soon as it was energized, the GFCI tripped. A sensitive clamp-on current meter showed a ground current of 52 mA, which was more than enough to trip the GFCI in less than 1 second.
The second instance was a plasma cutter, which was similarly connected through the GFCI. Everything was normal when the unit was turned on, but as soon an arc was struck the GFCI tripped, with ground current in excess of 20 mA.
These last two experiences provide good examples of applications in which an EGFPD would be appropriate. As stated, and EGFPD does not qualify as a GFCI, but its ground conductor monitoring function fulfills the requirement for an assured equipment grounding program.
Meeting the requirements
OSHA regulations require an expensive and time-consuming assured equipment grounding conductor program in cases where a suitable GFCI is not available for temporary wiring used in "construction-like" activities in industrial installations. The recent introduction of industrial special-purpose GFCIs has made it possible to eliminate these programs in many cases, and extend GFCI protection to places where it was not previously available. In cases where a GFCI cannot be used because of excessive ground current during normal operation, an EGFPD can often be used at a considerable savings in money and effort.
Nehad El-Sherif is technical product specialist for Littelfuse Startco in Saskatoon, Saskatchewan, Canada.