"250.112(I)  Power-Limited Remote-Control, Signaling, and Fire Alarm Circuits.  Equipment supplied by Class 1 power-limited circuits and Class 1, Class 2, and Class 3 remote-control and signaling circuits, and by fire alarm circuits, shall be grounded where system grounding is required by Part II or Part VIII of this article."

    For AC circuits that are 50 volts or less:  "250.20(A) Alternating-Current Circuits of Less Than 50 Volts. Alternating-current circuits of less than 50 volts shall be grounded under any of the following conditions:  
    (1) Where supplied by transformers, if the transformer supply system exceeds 150 volts to ground
    (2) Where supplied by transformers, if the transformer supply system is ungrounded
    (3) Where installed as overhead conductors outside of buildings" 

    However, SHORT SECTIONS OF RACEWAY, do not always have to be grounded. Section 250.86 Exception No. 2 - "Short Sections of metal enclosures used to provide support or protection of cable assemblies from physical damage shall not be required to be grounded."


Most two wire transformers are a separately derived Alternating Current System requiring a grounding electrode conductor.  Section 250.30 has the rules for this type of grounding.  Separately derived AC systems are grounded when required to be grounded by Section 250.112.

250.30(A)(3) Exception No. 3 states "A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the system grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134."

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