I had more of this info posted in another thread, of which I can't find any longer. And this one too. https://www.electrical-contractor.net/ubb/Forum1/HTML/005673.html
Its a 75HP motor. 1300+ LRA on a soft start pulling 650A+ Its a BEAST! http://www.markhellerelectric.com/motordata.htm
Soft Start is a Thyssen Dover Krupp 787AC-14
Of which I can find little information on. But simular to this one: http://www.elevatordrives.com/resources/hpv100_techmanual_tm5590.pdf
Feed is about 175' as the crow flies, but I got down there to map out a path and turns out to be 230+' of 250MCM. And has some exessive voltage drop, down from 208 to 180V at start.
Anyway, this thing has been battled out a few different ways. Elevator guy says its the feed, the electrician who installed the feed says its the elevator. And owner of it is confused and going for what makes sense to him.
Elevator guy suggested the foam filled conduit idea, the same as SteveFehr. But since this feeder heats up in frequent use, and it being a bad idea anyway, I laughed hyserically when I heard it. I should then derate the run for fill at 100%? He also suggested the triplexing idea...
Then theres me: I don't think Upping the size of the conductors to 350MCM is going to do anything except a slightly lower pitched rattle. 350 and triplexed I think will help. But the high in-rush will still be there. Many other people have had various thoughts on it, and range from locked up hydro pump, pump valves opening or closing during improperly timed during in-rush below speed, reversed windings, bad starter, voltage drop, triplexing, etc. no one whats to stick a 43B with 1000A, or 3000A CT's on the main to learn any more about the problem for a few hundred bucks, but would rather spend a few thousand on changing out the wire. And our PM bit on this agaist my judgement on staying away from it. She's pricing it for a regular 350 run in exiting conduit (Probhably too low as usual), and they'll bite. So guess who gets to pull it, me and my crew.
Now on a different note: I have some interesting expeirances with large motor starting.
While in the military, we had RO machines with 100HP pumps, which ran rather well on a 60KW gen set, but start-up would rock the gen set pretty harshly. Most of the time we would paralell up 2 60's for start, and use 1 to run. The cable we used for it was 250/4. (FYI most cables are twisted/triplexed.) Which would kind of jolt a bit at start, noticable. We ran out of that once, and used 4/0-4, and it would flex like a snake very noticably for the first few seconds of start-up, kinda wriggle a bit slowly. Ran out of both on occassion, and used THW individual conductors, no conduit as it was a temp feild operation in Somalia, the conductors jumped all over the place. So I figure triplex will help, to what degree, I don't know. As this elevator feeder rattle is like nothing I have ever heard. Imagine a 20A on 12's short circuit in 1/2", 1000%.