Shared AC bus on kinetix 5500 drives

I'm working on a project using a few kinetix 5500 drives, and I can't seem to get a straight answer from co-workers on power setup. I know you can use a shared AC bus, but AB literature states that you can only do so if the drives are the same (i.e. you can't put an H003 drive on the same power bus as an H008 drive). My co-workers said that it's not an issue and they've been doing it for years, so I'm trying to figure out if it's actually ok and just rockwell being overcautious or if there's a legitimate reason you shouldn't do it.

Do you mean a common DC bus but with each drive also receiving its own AC supply or do you mean no shared bus but a shared AC supply?

In the first case you want matched drives but in the second case it doesn't matter.

Does each drive have its own circuit protection or is that what you mean by "shared AC"?

Keith

Yes, I think you are missing that the “no mismatch” rule applies to shared Dc bus setups.

That's what I thought, but per AB's literature:



What I've been told is that it's fine to share the AC bus and control bus on a single breaker without sharing the DC bus, but as you can see above, AB states you can only do that if the drives are all the same, hence my confusion.

I wonder if what they are stating is that to use the proper input protection fusing/breaker, in the single feeder/multiple drive configuration, the drives must be the same rating. Otherwise, the input protection would be too high or low.

I can only assume this applies to an application where only one drive is motoring at a time. If the DC bus were shared, 2 could be motoring while 1 was regenerating.