Hi,
When adding ATS or Breakers to spare cubicles/sections of MCC, how does contractor typically connect new equipment to existing bus? It seems like the easiest way would be to drill and mount lugs onto existing bus and run cables from the terminals of new device to/from the bus. Another alternative would be to measure out the length from the device terminals to the bus and then procure bus segments, assuming we've got a nice symmetry.
Perhaps this is typically contracted out to system integrator who specializes in the MCC retrofits and they figure out the best approach for application.
Thanks,
EE
You are describing something that is trickier than most people realize.
Any modifications done to the
power structure of an MCC by anyone other than the mfr of the MCC will void the UL845 listing not just of the unit that was modified, but if any one unit is voided, it voids the listing of the entire lineup.
That said, people do it all the time because once an MCC is installed, inspected and passed, the UL listing of it becomes less critical,
to the installer. It might still be an issue for the
end user because their insurance company may have a requirement that all electrical equipment be UL listed. UL stands for "Underwriter's Laboratories", as in
INSURANCE underwriters. That's what their original purpose was and continues to be.
Most ATS units are not UL845 listed at all, ever, so that's why what you usually see in an MCC from a factory is that an ATS is put into a section that has no bus bars and is cable connected to the MCC bus using factory bus lugs. If there are no bus bars in a section, it doesn't need UL845 listing, so the ATS will have it's own UL1008 listing applied to it.
Feeder breakers will be plug-in up to a certain size (some stop at 250A, a few go to 400A with a plug-in). Above that there will be no legal way to add a breaker to an existing section, you must buy a new section with the large breaker factory mounted and either add it on to the end of the lineup or swap out an existing section (which gets tricky if there are shipping spits involved).
Most System Integrators cannot modify POWER connections in MCCs either (although some don't seem to know that). Panel shops usually have UL508A listing, which allows them to modify CONTROL circuits in an MCC,
but not power. That's partially because EVERYTHING that is in the power circuit MUST be tested for short circuit AND withstand IN THE MCC, regardless of whether it has been tested and listed elsewhere. It also must pass the MCC's temperature rise requirements, which is why a lot of things often seem to have more space than we might think necessary when ordered from the mfr.
There are a FEW SIs across the country (maybe 3 or 4?) that have made arrangements with one or two MCC manufacturers to act as MCC assembly facilities under THE MANUFACTURER'S license for UL845. But most mfrs will not do that because it is VERY risky for them. If the SI makes a blunder in something they do and UL catches it, the MANUFACTURER can lose their ability to apply UL845 labels to EVERYTHING they make anywhere! As it so happens, one of the few SIs in the nation that have this arrangement is in California where you are, so maybe you have been talking to them, I don't know. But it does not mean they can do anything they like, they can still only do what the MCC mfr has ALREADY listed in their own files and they can of course only modify MCCs made by that one mfr.
