The provisions of 230.95 covering the ground-fault protec-
tion of equipment were first required in the 1971 Code due
to the unusually high number of equipment burndowns re-
ported on large capacity 480Y/277-volt solidly grounded
services. This section requires ground-fault protection of
equipment for each service disconnecting means rated 1000
amperes or more where the supply system is solidly
grounded, wye-connected, and operates at more than 150
volts to ground and not more than 600 volts phase to phase.
See the definition of ground-fault protection of equipment in
Article 100. Systems operating at 480Y/277 volts were cited
in the original substantiation for this requirement, but there
are other solidly grounded, wye-connected systems (i.e.,
600Y/347) that are covered within the parameters specified
by this section. This requirement does not apply to systems
where the grounded conductor is not solidly grounded, as is
the case with high-impedance grounded neutral systems
covered in 250.36.
Ground-fault protection of services does not protect the
conductors on the supply side of the service disconnecting
means, but it is designed to provide protection from line-to-
ground faults that occur on the load side of the service dis-
connecting means. An alternative to installing ground-fault
protection may be to provide multiple disconnects rated less
than 1000 amperes. For instance, up to six 800-ampere dis-
connecting means may be used, and in that case ground-
fault protection would not be required. Informational Note
No. 2 to 230.95(C) recognizes that ground-fault protection
may be desirable at lesser amperages on solidly grounded
systems for voltages exceeding 150 volts to ground but not
exceeding 600 volts phase to phase.
In addition to providing ground-fault protection, engi-
neering studies are recommended to determine the circuit
impedance and short-circuit currents that would be available
at the supply terminals, so that equipment and overcurrent
protection of the proper interrupting rating are used. See
110.9 and 110.10 for details on interrupting rating and cir-
cuit impedance.
The two basic types of ground-fault equipment pro-
tectors are illustrated in Exhibits 230.27 and 230.28. In
Exhibit 230.27, the ground-fault sensor is installed around
all the circuit conductors, and a stray current on a line-to-
ground fault sets up an unbalance of the currents flowing in
individual conductors installed through the ground-fault
sensor. When this current exceeds the setting of the ground-
fault sensor, the shunt trip operates and opens the circuit
breakers.
The ground-fault sensor illustrated in Exhibit 230.28 is
installed around the bonding jumper only. When an unbal-
anced current from a line-to-ground fault occurs, the current
flows through the bonding jumper and the shunt trip causes
the circuit breaker to operate, removing the load from the
line. See also 250.24(A)(4), which permits a grounding elec-
trode conductor connection to the equipment grounding ter-
minal bar or bus.
