Grounding, Bonding, and Overcurrent Protection for Low-Voltage Systems
What this domain tests
Grounding, bonding, and overcurrent protection make low-voltage systems safe and functional. The exam tests Article 250 fundamentals, grounding electrode systems, equipment grounding conductors, separately derived systems, and overcurrent protection for Class 1 and low-voltage power supplies.
Core rules
- A grounding electrode system must be bonded together per 250.50; the grounding electrode conductor is sized from 250.66.
- Equipment grounding conductors clear faults and are sized from 250.122 based on the overcurrent device.
- Separately derived systems, such as a grounded 24 V transformer secondary, are bonded per 250.30 if the system is grounded.
- Class 2 and Class 3 circuits are generally not required to be grounded; do not create a ground connection that the listing does not permit.
- Class 1 circuits need overcurrent protection per Article 725; power supplies must be listed and protected.
Worked example
A control panel has a 24 V power supply with a grounded secondary and a 5 A output breaker. Bond the secondary to the equipment grounding bus as required for the grounded system, and size the equipment grounding conductor from 250.122 using the 5 A device. If the supply is listed as a Class 2 source, do not add a grounding connection unless the instructions require it.
Traps
- Using the neutral as an equipment ground.
- Grounding only to a water pipe without the electrode system.
- Undersizing the equipment grounding conductor.
- Adding a ground to a Class 2 circuit that is not listed for it.