DaveBones...
Some advocates of Soft-Start controllers claim that the number of starts/hr is (without concern about size) "virtually" unlimited!
It's unfortunately true that some people say this, but they are wrong! You CANNOT increase the Starts-per-Hour capability of a motor by adding a soft starter. It does nothing to change the physics involved in acceleration nor the energy that goes into it. The curve of energy is the same in either case; Across-the-Line starting is a very high steep curve of short duration, Soft Starting is a lower curve but much wider. All you are doing is trading height for width, the area of the curve, representing the energy (and thereby the heat) going into the motor, is always the same no matter what.
For conventional starting methods, I would consider 10 per/hour as extreme!
Regardless of the starting method employed in this situation (testing?) I would contact the motor manufacturer!!
Phil
Phil is right, 10 starts/hour on a 150HP motor is extreme for sure, the standard design would be for around 3 starts/hour. But that is
IF the load actually requires 150HP. If you NEED more starts per hour out of a motor, you can de-rate the motor. So if this is a 50HP load but they want to start it every 6 minutes, THAT may be why it has a 150HP motor on it. We just can't say from here, even the motor mfr can't answer that question, only the machine designer knows that for sure.
Nonetheless, the FUSE may be the weak link in this scheme anyway because IT requires a certain amount of time to cool down from the inrush and starting current. The fact that it only blows occasionally means that it is close to working reliably, just not quite there. One way you could possibly help it is to address what gar said about the fact that sometimes they are likely not waiting at all, so it's not really every 6 minutes. Get a motor protection relay that has a programmable "Minimum Time Between Starts" feature, or make one from a timer. Set it for 6 minutes and prevent them from restarting that motor too quickly, most likely that will solve the occasional fuse clearing. Give them a little light on the front panel that goes green when they can start it again.
I would not do it, but if you do decide to increase the fuse size instead, make sure it fits within the NEC rules, but also read the information on the overload relay. They are designed to be used with a maximum fuse size and if you exceed it, you are putting it at risk.
I'd be looking for the starter to pass me as I was running.