590.8 Overcurrent Protective Devices.
Code Change Summary: New code section on reusing temporary electrical equipment.
Many electrical companies will use and reuse temporary electric panelboards, transformers and services, setting them up at the beginning of a construction project and then removing them after the project is complete. During this process, lots of wear and tear can occur.
It can be difficult for an inspector to give a green tag on a temporary power installation with used equipment that may have been subjected to something on a past job site that is not visibly obvious such as water damage or harsh environments.
In the 2020 NEC®, this was addressed with new code language. Now, where overcurrent protective devices that have been previously used are installed in a temporary installation, these overcurrent protective devices must be examined to ensure they have been properly installed, properly maintained, and there is no evidence of impending failure. This language aligns with similar language in NFPA 70E Standard for Electrical Safety in the Workplace.
Additionally, overcurrent devices for solidly grounded wye electrical services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase must be current limiting. A current limiting device will trip within the first half cycle of a sine wave during a fault condition. Tripping within the current limiting range ensures the fastest possible elimination of the overcurrent condition thus reducing the level of hazard exposure to the workers.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.
2017 Code Language:
This code section did not exist.
2020 Code Language:
N 590.8 Overcurrent Protective Devices.
N (A) Where Reused. Where overcurrent protective devices that have been previously used are installed in a temporary installation, these overcurrent protective devices shall be examined to ensure these devices have been properly installed, properly maintained, and there is no evidence of impending failure.
N (B) Service Overcurrent Protective Devices. Overcurrent protective devices for solidly grounded wye electrical services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase shall be current limiting.
Informational Note: The phrase “evidence of impending failure” means that there is evidence such as arcing, overheating, loose or bound equipment parts, visible damage, or deterioration. The phrase “properly maintained” means that the equipment has been maintained in accordance with the manufacturers’ recommendations and applicable industry codes and standards. References for manufacturers’ recommendations and applicable industry codes and standards include but are not limited to NEMA AB 4-2017, Guidelines for Inspection and Preventative Maintenance of Molded-Case Circuit Breakers Used in Commercial and Industrial Applications; NFPA 70B-2019, Recommended Practice for Electrical Equipment Maintenance; NEMA GD 1-2016, Evaluating Water-Damaged Electrical Equipment; and IEEE 1458-2017, IEEE Recommended Practice for the Selection, Field Testing, and Life Expectancy of Molded-Case Circuit Breakers for Industrial Applications.