can anyone please tell me what code article I would find information on about generator interlock switches. i'm looking to install one of those interlock switches that mounts on the panel cover itself and allows for a portable generator hook-up, but wanted to make sure that it meets the NEC. thanks in advance!
Most information on interlocks and their requirements are found in the standard for transfer switches - UL 1008. The NEC requires an approved transfer switch and reverts to UL 1008 / UL 67 for the requirements of such equipment.
My suggestion would be to only use the offered interlock by the panel maker you have, it has to be listed on the cabinet label with its part number. According to UL 67 standard for panel boards, any mods (parts/accessories) to a panel have to be listed on the panel label. I'm sure that there are numerous cases of subjectively less significance where this (in general) isn't a concern to a lot of people, such as adding a GE breaker in a Siemens panel. But the lock out mechanisms for a feed in generator breaker are quite more important in my opinion compared to a different brand of breaker in a different brand of panel.
Aftermarket kits (not made by the panel companies) are not listed by NRTL's and could be defeated pending their design and could also void the listing of the panel board if installed.
Yet these aftermarket kits still probably pass inspections in various cases, but I believe a conclusion can be made that all aftermarket kits violate the NEC since it results in a modified panel board with an unlisted accessory not made by the company that made the panel board.
That is news to me. You can often get one from the panel maker.
For example Square D sells interlock kits for its own panels.
Exactly. Most panel makers offer they own proper interlock kits as accessories and they are always listed on the panel labels as part numbers. Of course not all panels have this option, if they are older or the panel maker didn't have the foresight or make the decision to offer an add on accessory bracket for a generator breaker. This is where the after market 3rd party interlocks come into play, but I have YET to see anything in this regard that is NRTL listed that would meet code.
About the only thing that specifically applies is 702.5.
702.5 is pretty general about transfer equipment, it must work according to the reason for its requirement (isolate primary and alternate power supplies at all times) it really doesn't go into any specific methods or types of equipment beyond a few bits and pieces of load side overcurrent protection.
UL 1008 is the go to, and also requires that the mechanism itself cannot come off with the dead front if it's removed, and it MUST be bolted to the cabinet so that it can't be defeated with the dead front off unless someone intentionally removes the interlock mechanism to allow both input breakers to be ON. The GEN breaker also cannot be removed unless the interlock is removed intentionally, the point is UL doesn't want it to be easy to defeat an interlock. Some of the aftermarket interlocks (not made by panel makers) do not meet these requirements, and again, none I know of are listed equipment.
