440.9 Grounding and Bonding.
Code Change Summary: A new code section was added to address HVAC equipment grounding and bonding when metal raceways are involved.
Several public inputs were submitted this code cycle to require a wire type equipment grounding conductor for rooftop HVAC equipment. There are many types of equipment grounding conductors permitted in 250.118 ranging from a wire type conductor to using certain types of metal raceways as the actual equipment grounding path.
Electrical metallic tubing (EMT) is one type of acceptable equipment grounding conductor listed in Section 250.118. When installed properly and the fittings are made up wrench-tight, EMT is an excellent equipment grounding conductor.
For the 2017 NEC®, a new section was added to address proper equipment grounding of multimotor and combination-load equipment installed outdoors on rooftops. Most rooftop air conditioners and other types of HVAC equipment are considered multimotor and combination-load equipment due to the nature of the equipment and multiple loads incorporated into each unit.
The new code section states: Where multimotor and combination-load equipment is installed outdoors on a roof, an equipment grounding conductor of the wire type shall be installed in outdoor portions of metallic raceway systems that use non-threaded fittings.
The intent is to address a common occurrence where a non-threaded raceway such as EMT is installed and the fittings either come loose or were never made up wrench-tight to begin with. In this case, the equipment grounding path is compromised and the metal raceway may not provide a reliable return path during a ground-fault condition.
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 2017 NEC® edition of NFPA 70.
2017 Code Language:
N 440.9 Grounding and Bonding. Where multimotor and combination-load equipment is installed outdoors on a roof, an equipment grounding conductor of the wire type shall be installed in outdoor portions of metallic raceway systems that use non-threaded fittings.