Gemini Instruction Manual I-GARD
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5
APPENDIX 1
5.1 high-Resistance grounding
Both the Canadian Electrical Code, Part 1, C22.1-98 and the National Electrical Code, NFPA 70 1999,
approve the use of high-impedance grounding neutral systems up to 1000 V. A.C. where the ground fault
current is limited to 5 amperes or less. These new changes to the electrical code allow users of the Gemini
to maintain a ground fault current of 5 amperes or less on their electrical distribution system without shutting
down because of a single ground fault, thereby avoiding unscheduled down times. Gemini users can locate,
isolate and repair faulty equipment at convenient time.
The reason for limiting ground fault current by resistance grounding may be one or more of the following, as
indicated in IEEE Std. 142-1991, IEEE Recommended Practice for Grounding of Industrial and Commercial
Power Systems
,
pp. 25-26.
1 ) To reduce burning and melting effects in faulted electric equipment, such as switchgear, transformers,
cables, and rotating machines.
2 ) To reduce mechanical stresses in circuits and apparatus carrying fault currents.
3 ) To reduce electric-shock hazards to personnel caused by stray ground-fault currents in the ground
return path.
4 ) To reduce arc blast or flash hazard to personnel who may have accidentally caused or who happen to
be in close proximity to the ground fault.
5 ) To reduce the momentary line-voltage dip occasioned by the occurrence and clearing of a ground fault.
To secure control of transient over voltages while at the same time avoiding the shutdown of a faulty circuit
on the occurrence of the first ground fault.
5.2 Definitions and Applicable Standards
Grounding means a permanent and continuous conductive path to the earth with sufficient ampacity to
carry any fault current liable to be imposed on it, and of a sufficiently low impedance to limit the voltage rise
above ground and to facilitate the operation of protective devices in the circuit;
Bonding means a low impedance path obtained by permanently joining all non-current-carrying metal
parts to assure electrical continuity and having the capacity to conduct safely any current likely to be
imposed on it;
