Code Change Summary: Requirements have been added for documenting the short-circuit current rating of emergency system transfer equipment.

Transfer equipment is already required to be marked with the short-circuit current rating (SCCR) per UL 1008 which covers transfer equipment. UL 1008 has many options for short-circuit protection. Transfer switches are usually marked by the manufacturer with several different combinations resulting in many options to choose from to ensure proper SCCR values.

These marked SCCR values can vary based upon the overcurrent protective device type, ampere rating and settings. The transfer switch in the image has a SCCR of 65,000 amps at 480 volts when protected by a Square D Type PJ circuit breaker not larger than 1200 amps. The same transfer has a SCCR of 200,000 amps at 600 volts when protected by a Class L fuse not larger than 1200 amps. When inspecting the specific installation, it can be confusing for an inspector to know which SCCR is valid based on the combination selected by the engineer for the specific project.

To solve this issue, in the 2017 NEC^®, the short-circuit current rating of the transfer switch, which is based on the specific overcurrent protection provided, is now required to be additionally field marked on the equipment.

The new code section doesn’t provide any insight on the type of label required.

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.