[KenB]

Does a 2 speed motor have to have a mechanically interlocked starter?
I have a piece of packing equipment, screw packer, that is continual blowing the 480v fuse(s) that feed the panel. Two separate starters low speed and high speed. They are electrically interlocked only. Change fuses and it takes off.
This happens intermittent. Can't find any other source of the problem. Thinking one starter may not be dropping out in time and both are engaged for a second pulling locked rotor?

 

[micromind]

If both high and low speeds are energized at the same time, the current will be quite a bit higher than normal locked-rotor.

If the starters are mechanically interlocked, and both coils are powered at the same time, they'll very likely jam up.

I'd install a time-delay relay on each coil. That way if one coil was energized before the other one dropped out, they wouldn't both be closed at the same time.

 

[sparkywannabee]

What exactly is a 480v fuse. Are you sure your 'interlocked starters' is not just a forward/reversing motor starter and the speed is controlled some other way, because i have never seen speed controlled through the starter, usually you have a drive or maybe resistors.

 

[JRaef]

Does a 2 speed motor have to have a mechanically interlocked starter?
I have a piece of packing equipment, screw packer, that is continual blowing the 480v fuse(s) that feed the panel. Two separate starters low speed and high speed. They are electrically interlocked only. Change fuses and it takes off.
This happens intermittent. Can't find any other source of the problem. Thinking one starter may not be dropping out in time and both are engaged for a second pulling locked rotor?

Depending on the type of two speed motor, changing speeds too fast can cause this. If you have only 2 contactors, it is a 2 speed 2 winding motor. If you change from High to Low too quickly, the magnetic field in the motor is still there from the High speed winding and when you energize the Low speed windings, the relative frequency is higher than that of the low speed winding and the motor regenerates, but out of phase with the line. It creates a massive spike that can take out fuses, if not twist off shafts. You need a delay of at least a half second when transitioning from High to Low, it's standard fare if you bought an official 2S2W motor starter or if there was a mechanical interlock it forces the time delay, but if people "roll their own" they often miss that detail.

 

[JRaef]

What exactly is a 480v fuse. Are you sure your 'interlocked starters' is not just a forward/reversing motor starter and the speed is controlled some other way, because i have never seen speed controlled through the starter, usually you have a drive or maybe resistors.

Seriously? You've never heard of 2 speed motors?

There are two types, 2 speed 2 winding (2S2W), which is almost like having two separate motors, or 2 speed 1 winding (2S1W) where there is one set of windings that are reconfigured externally with a set of 3 contactors. 2S1W motors then come in 3 types, depending on the speed ratio you want and/or the torque differences.

 

[KenB]

Good info thanks. This panel definitely has been "tweaked" over the years. This really seems a likely issue with the starters.

Simply meant the fuse on 480 panel feed.
It's a 2 speed motor no doubt.

 

[sparkywannabee]

Thanks for the educamation JRaef. I don't get out much, never came across a motor using different windings for different speeds.