disconnect interlocking

[mwklein]

Does NEC 2005 require that the main disconnect in an industrial control panel be mechanically or electrically interlocked? I cannot find it anywhere in my NEC book. The only code I can see that requires it is NFPA 79 according to 5.3.1.4 and 6.2.3. Am I missing something?

Also, is there a specific SCCR rating that an industrial control panel needs to be designed to, or is it just that the actual SCCR rating needs to be displayed?

 

[hmspe]

Does NEC 2005 require that the main disconnect in an industrial control panel be mechanically or electrically interlocked? I cannot find it anywhere in my NEC book. The only code I can see that requires it is NFPA 79 according to 5.3.1.4 and 6.2.3. Am I missing something?

Also, is there a specific SCCR rating that an industrial control panel needs to be designed to, or is it just that the actual SCCR rating needs to be displayed?

What do you mean by "interlocked"? Your first question is not clear.

On the SCCR, the panel would have to be suitable for the calculated short circuit current that the distribution system can provide at the line terminals of the panel. That will be different for different facilities, so there's no generic value that will work for all installations. If you want to be suitable for probably 98% of installations you can use 65K for a 120/208V panel and 42K for a 277/480V panel.

Martin

 

[mwklein]

By "interlocked" I mean that the door of the enclosure is not able to be opened if the disconnect power is on (see NFPA 79 6.2.3).

 

[jim dungar]

The NEC does not require an integral disconnect to be mechanically interlocked with the enclosure door. This requirement is only in NFPA79.

5kA is the minimum rating of UL Listed/Recognized electrical equipment and is to be the assume maximum SCCR value unless the manufacturer of the control panel provides a different value.