Special rules for ground-fault protection of equipment (GFPE) apply to healthcare facilities. Section 517.17(A) indicates that these GFPE rules apply to hospitals and other buildings (including multiple occupancy buildings) with critical-care space or where life-support equipment is used. It is also required for other buildings that provide essential utilities or services for the operation of critical-care space or electrical life-support equipment.


According to Section 517.17(B), when ground-fault protection is provided at the service or feeder disconnecting means as specified by 230.95 or 215.10, an additional level of ground-fault protection must be installed in the next level of feeder disconnecting means downstream toward the load. GFPE typically consists of overcurrent protective devices, current transformers and relays, and equivalent protective equipment that rapidly responds to ground-fault events. The primary purpose is so that a ground-fault event in the electrical system does not open the service GFPE disconnecting means. Instead, it opens the device closest to the fault, thus isolating or localizing the offending circuit, while maintaining power continuity to the rest of the facility. According to 517.17(C), additional levels of GFPE are not permitted on the load side of an essential electrical system transfer switch.


Service and feeder GFPE is required to be 100 percent selective so that, if a ground fault occurs downstream from the feeder overcurrent device, only the closest overcurrent device will open and the upstream devices will remain closed. Of course, this requirement is in place to prevent the blackout of a facility caused when a main could open for a fault that should be isolated to a single feeder. To achieve this coordination, 517.17(c) requires adequate separation between the service and feeder tripping bands. This is accomplished by adjustable settings of time and current characteristics of the equipment. 


Each level of ground-fault protection equipment must also be performance-tested when first installed. It is critical to ground-fault protection system functionality that the grounded (neutral) conductor be completely isolated from any downstream grounding connections. This is a general requirement of the NEC in Section 250.24(A)­(5) and is a specific requirement of the manufacturer’s installation and testing instructions for the GFPE [NEC 110.3(B)]. This is especially important where transfer switches and alternative-power sources are installed in the premises-wiring system. In most cases, four-pole transfer switches are installed on three-phase, 4-wire systems so as to allow the system to function properly without grounding connections to the neutral or grounded conductor downstream from the service disconnecting means that includes GFPE for that particular separately derived system.


Feeder ground-fault protection


Section 215.10 requires this protection for feeders that are of the same voltage and current rating as similar services.


This is an example of a situation where the electrical system is provided by a service or feeder with a voltage of more than 600 volts (V), say 12,470V, and has the service or feeder disconnecting means rated at that voltage level. Often part of a unit substation, a transformer then reduces the voltage of the feeder to the level where equipment ground-fault protection is required, typically 480Y/277V, three-phase, 4-wire wye-connected. The risk of destructive arcing burn-downs is the same, regardless of whether this system is a service or feeder. The same exceptions that are provided to Section 230.95 for services are also provided for 215.10 for feeders. However, care must be exercised to be certain that each new voltage system, created through transformers or other sources, has the necessary protection required. If it qualifies for equipment ground-fault protection by the voltage and ampacity level of the feeder and equipment, it must be provided.


Required testing of GFPE


Sections 230.95(C) and 517.17(C) require ground-fault protection systems to be performance-tested when first installed on-site to ensure proper operation. Experience has shown that the majority of these systems do not operate properly, or at all, when first installed. This is far more than a “push button” test. All testing must be performed in full compliance with the manufacturer’s written instructions, which are usually furnished with the equipment.


A vital part of the test is to remove the neutral-disconnect link in the service equipment and test the neutral with a continuity tester or megohmmeter to be certain that it is completely isolated from any grounding connections on the load side of the service disconnect. Accidental or intentional grounding connection to the grounded (neutral) conductor past the GFPE device can render ground-fault protection systems ineffective. Written records of the performance test are required to be made available to the authority having jurisdiction. Electrical system and equipment safety requires the GFPE to be properly installed and performance-tested.