Star-Stop Motor

It depends on what the motor manufacturer says, and also on how severe the starting conditions are. Some commonly seen values are around 6-10 starts per hour, but I have some screw compressors in my plant that are limited to 3 per hour.

I'll back that up, there are no general "rules" when it comes to large MV motors, everything depends on the original tender offer and what was requested. So the only viable answer will have to come from the motor mfr by providing them with a serial number.

I don't think 6-10 starts per hour is a very common spec for MV motors, it's usually much less. Looking at a couple of projects I did, the motor data sheets say 1 hot start plus 2 cold starts per hour on two of the motors. This is the NEMA MG-1 basic spec, but you have to keep in mind that this is based on the LOAD INERTIA that the specific motor was designed for. So if your load inertia is different that that of the original intent of the motor when manufactured, then those numbers mean next to nothing. And that is even assuming the motor was designed to that standard, which itself is not guaranteed. I remember working on one motor that someone bought used off of a fan and he wanted to put it on a rubber shredder. I paid Westinghouse for the old archived data sheets and discovered that it had been designed for 1 cold stat + 1 hot start PER DAY!

Right if we're going for bombproof totally indestructible motors then look for "foundry rated crane motors". Best of luck, I don't think they're made as far as I know now a days!

It took me the best part of a month to find out how to get the end bells off one!

Best bet would be the motor data sheet.

Thanks, J, for the further note. I kind of overlooked the MV and was speaking more toward "garden variety" LV motors. (I've been around some MV gear, but never have operated or designed any.)

same. The difference is, with LV you have to find it and touch it to get hurt. With MV it finds you if you are just close, and with HV it hunts you down!