[JRaef]

I couldn’t find any reference to that motor designation, but “E-Line” makes me think this is an energy efficient (EE) motor design. It’s well known that many EE motors attain their high efficiency by messing with the magnetics, often resulting in very high magnetic inrush currents which can blow fuses and trip breakers. It will appear random because there are other factors involved in allowing it to happen, but when it is a repeating event like this, that is my suspicion.

This is the reason why an exception was added to 430.52 to allow mag trip settings to go as high as 1700% if it is demonstrated that lower settings result in nuisance tripping. As for fuses, you absolutely must use time-delay type, but often you must go to the maximum allowable fuse size to avoid nuisance clearing. Given the thorough investigation you have already done to eliminate other obvious issues, these measures are warranted IMHO.

 

[JRaef]

I looked at the spec sheet and the motor is indeed a "Premium Efficiency" motor so that seems to be the cause.

I found an ABB white paper on the subject so I have attached it if anybody is interested in learning more. I didn't know about this until @JRaef brought it up. Apparently the new energy efficient transformers also have higher inrush currents than previously seen.

thanks to everybody for the help.

You are not alone in discovering this the hard way...

Back in the early 90s I got pulled into a lot of projects where people were getting utility rebates for changing out old motors for new EE motors. But right away, we started seeing a LOT of tripping circuit breakers and blown fuses, as in 75% of installations! The utility rebates were being pushed by the US Dept. of Energy under a program called "Motor Matters" and they got involved right away to have someone study it. That study was done by the Electric Power Research Institute (EPRI) who was already doing a lot of studies on motor efficiency and failure rates at the time. EPRI concluded that the change in magnetics (and air gap reduction) to attain the higher energy efficiency also had the side effect of lowering the winding resistance and initial impedance (before the motor starts to rotate), resulting in much higher magnetic inrush than had been previously seen. Most of the papers now released by motor manufacturers and others in North America are all based on the study done by EPRI in the 1990s. I know this because I was so deeply involved in the rebate programs in the Pacific Northwest at that time, I was given an associate membership in EPRI and was able to access their papers. But I no longer am and have to pay-to-play like everyone else, so I don't have the name of that study to link to it any more. But papers like the one previously linked are probably using that data (although ABB being a foreign company, appear to claim it all came from Europe...). But here is a much later (2012) paper from the successor of the Motor Matters program in the DOE, dealing with just the Mag-Only Breaker issue, the problem extends to fuses too.

https://www.energy.gov/sites/prod/files/2014/04/f15/avoid_nuisance_motorsys_ts6.pdf

 

[JRaef]

Lol, yeah I had a few uncomfortable conversations about the slight change in speed too. On most fans it took a simple sheave change to correct for it, but direct drive pumps were harder to deal with. We had to have them add throttling valves if they didn’t already have them, which represented an energy loss, so the net change in energy use was often zero or close to it. Trimming the impellers was the real solution in some, but they had to wait to take them out of service for a PM to get that done. As I said, “uncomfortable”…