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AC circuits and systems supplying premises wiring shall be grounded as provided for in this Section.
(a) AC circuits of less than 50 volts shall be grounded under any of the following conditions:
(1) Where supplied by transformers if the transformer primary supply system exceeds 150 volts to ground.
(2) Where supplied by transformers if the transformer primary supply system is ungrounded.
(3) Where installed as overhead conductors outside of buildings.
(b) AC systems of 50 volts or more shall be grounded under any of the following conditions:
(1) Where the system can be so grounded that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts.
(2) Where the system voltage is rated 3-phase, 4-wire wye-connected in which the neutral is used as a circuit conductor.
(3) Where the system voltage is rated 3-phase, 4-wire delta-connected in which the midpoint of one phase is used as a circuit conductor.
(4) Where a service conductor is uninsulated.
Exceptions: AC systems of 50 volts or more are not required to be grounded under any of the following conditions:
1: Electric systems used exclusively to supply industrial electric furnaces for melting, refining, tempering, and the like.
2: Separately derived systems used exclusively for rectifiers supplying only adjustable speed industrial drives.
3: Separately derived systems supplied by transformers that have a primary voltage rating less than 1000 volts provided that all of the following conditions are met:
a. The system is used exclusively for control circuits.
b. The conditions of maintenance and supervision assure that only qualified persons will service the installation.
c. Continuity of control power is required.
d. Ground detectors are installed on the control system.
4: Isolated power systems that supply circuits in health care facilities.
5. The system is a high-impedance grounded neutral system in which a grounding impedance, usually a resistor, limits the ground-fault current to a low value for 3-phase ac systems of 480 volts to 1000 volts provided all of the following conditions are met:
(a) The conditions of maintenance and supervision ensure that only qualified persons will service the installation;
(b) Continuity of power is required;
(c) Ground detectors are installed on the system; and
(d) Line-to-neutral loads are not served.
Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.
1. Repealer and new section filed 3-20-79; effective thirtieth day thereafter
(Register 79, No. 12). For history of former section, see Register 75, No. 42.
2. Editorial correction filed 11-2-83 (Register 83, No. 45).
3. Change without regulatory effect amending subsection (c) filed 8-1-94 pursuant to section 100, title 1, California Code of Regulations (Register 94, No. 31).
4. Amendment of section and Note filed 5-5-2008; operative 5-5-2008. Submitted to OAL for printing only pursuant to Labor Code 142.3(a)(3) (Register 2008, No. 19).
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