I-GARD Gemini Instruction Manual
10
250-36. High-impedance Grounded neutral Systems
High-impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits
the ground-fault current to a low value shall be permitted for 3-phase ac systems of 480 volts to 1000
volts where all of the following conditions are met.
1 ) The conditions of maintenance and supervision ensure that only qualified persons will
service the installation.
2 ) Continuity of power is required.
3 ) Ground detectors are installed on the system.
4 ) Line-to neutral loads are not served.
High-impedance grounded neutral systems shall comply with provisions (a) through (f).
a )
Grounding Impedance Location
The grounding impedance shall be installed between the grounding
electrode conductor and the system neutral. Where a neutral is not available, the grounding impedance
shall be installed between the grounding electrode conductor and the neutral derived from a grounding
transformer.
b )
Neutral Conductor
The neutral conductor from the neutral point of the transformer or generator to its
connection point to the grounding impedance shall be fully insulated.
The neutral conductor shall have an ampacity of not less than the maximum current rating of the grounding
impedance. In no case shall the neutral conductor be smaller than No. 8 copper or No. 6 aluminum or
copper-clad aluminum.
c )
System Neutral Connection
The system neutral connection shall not be connected to ground except
through the grounding impedance.
d )
Neutral Conductor Routing
The conductor connecting the neutral point of the transformer or
generator to the grounding impedance shall be permitted to be installed in a separate raceway. It shall
not be required to run this conductor with the phase conductors to the first system disconnecting means
or overcurrent device.
e )
Equipment Bonding Jumper
The Equipment bonding jumper (the connection between the equipment
grounding conductors and the grounding impedance) shall be an unspliced conductor run from the first
system disconnecting means or overcurrent device to the grounded side of the grounding impedance.
f )
Grounding Electrode Conductor Location
The grounding electrode conductor shall be attached at any
point from the grounded side of the grounding impedance to the equipment grounding connection at the
service equipment or first system disconnecting means.
CSa Canadian electrical Code Part 1, C22.1-98
Pg. 105-106
10-1100 Scope.
Rules 10-1102 to 10-1108 apply to the use of neutral grounding devices used for the purpose of controlling
the ground fault current or the voltage to ground of an alternating-current system.
