Most multimotor and combination-load equipment is already required by Section 440.4(B) to be marked with a short-circuit current rating (SCCR). The intent is so that the electrician and inspector can ensure compliance with NEC^® 110.9 and 110.10.

The only way to ensure the HVAC equipment is rated to handle the amount of short circuit current available is to first find out the maximum amount of Available Fault Current that could be delivered to the equipment during a short circuit condition and then to determine the SCCR of the equipment by looking at the nameplate. As long as the HVAC equipment has a SCCR equal to or greater than the available short circuit current, then the installation complies with NEC^® 110.10.

In the 2017 NEC^®, language requires motor controllers of multimotor and combination-load equipment to be installed in a location where the available short-circuit current does not exceed the SCCR of the equipment. As well, new subsection B states: “When motor controllers or industrial control panels of multimotor and combination load equipment are required to be marked with a short circuit current rating, the available short circuit current and the date the short circuit current calculation was performed shall be documented and made available to those authorized to inspect the installation”.

Knowing the amount of available short circuit current at the HVAC equipment is the first step in ensuring that the HVAC equipment is properly rated for the worst-case fault condition that it may see.

See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).