Code Change Summary: A new code section was added to address the short-circuit current rating (SCCR) for elevator control panels.

“Available short-circuit current” is the amount of fault current that can be delivered to the equipment during a short circuit condition originating at the equipment. A movement is occurring throughout the NEC^® to raise awareness of available fault current, short circuit current ratings (SCCR) and proper application of NEC^® 110.9 and 110.10 which have existed rather silently in the NEC^® for quite some time.

Section 620.16(A) now requires elevator control panels to be marked with their SCCR.

The intent is so that the electrician and inspector can ensure compliance with NEC^® 110.9 and 110.10. These code sections require a close look at things like overcurrent device ampere interrupt capacity (AIC), circuit impedance, circuit characteristics and SCCR’s of equipment. This is to ensure that the overcurrent device protecting the equipment is rated properly so that it can eliminate the fault condition before extensive damage occurs to the equipment.

Two options are given in order to determine the amount of available short-circuit current at an elevator control panel:

• Use a listed and labeled control panel assembly that is already marked with the SCCR.
• Establish the SCCR by an “approved method”.

The new informational note mentions UL 508A-2013 Supplement SB as an example of an approved method.

UL 508A Supplement SB requires a 3-step process to determine the SCCR of an industrial control panel:

• First, find out the lowest SCCR of any component in the control panel.
• Second, see if there are current limiting devices ahead of the control panel that will limit the actual amount of current available at the control panel during a short-circuit condition.
• Third, label the control panel with the SCCR based on the values obtained from steps 1 and 2.

620.16(B) is new and requires action based on the SCCR values marked on the control panel. An elevator control panel shall not be installed where the available short-circuit current exceeds its SCCR. This new rule aligns with the language in 110.10 that was first introduced into the NEC^® in 1965.

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

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.