I recently found something while troubleshooting that I am now having a (putting it politely) heated conversation with a co-worker about.
Equipment: 1.5 hp, 3 phase, 480 volt electric motor, line started, connected to a gearbox, further connected to a fairly constant load. The starter is powered directly by a momentary pushbutton used to jog a small part of the machine into place. Starter is fed by a Littlefuse 3-pole indicating fuse holder. The load on this motor is rarely above nominal current.
The operators complained that the motor would occasionally not respond to the pushbutton but it seemed random and might only last for one or two pushes of the button. It would then work properly for some time. One of the guys on another shift then mentioned that he had changed one of the fuses out a couple of times and that seemed to make the problem go away for awhile. This had been going on for some time before I had the opportunity to take a look at it.
The first time I was called for this I found that one of the poles of the fuse holder was lit indicating a blown fuse. However, the light did not look "right" to me, it seemed to be dimmer than I would expect. The really odd thing is that the motor was still operating normally, even though the fuse was showing blown. I shut the machine down and traced the circuit, finding a very old wirenut where the plastic cap had vibrated off exposing the coils in a conduit bodythat was very moist and rusty inside.
I replaced the conductors and cover on the conduit body (eliminating the splice) and have had no problems since. My theory is that the exposed wirenut was occasionally shorting to ground, causing the fuse to blow and that the motor was still drawing power through the indicator of the fuseholder. I wish I had experimented with this a little more before I repaired it but I needed to get the machine running again.
My co-worker says I'm full of @#$%. We don't see eye to eye on much, mainly due to, again putting it politely, the amount of motivation he shows and I really want some backup on this. Can anyone provide some insight on this? Am I crazy?
Equipment: 1.5 hp, 3 phase, 480 volt electric motor, line started, connected to a gearbox, further connected to a fairly constant load. The starter is powered directly by a momentary pushbutton used to jog a small part of the machine into place. Starter is fed by a Littlefuse 3-pole indicating fuse holder. The load on this motor is rarely above nominal current.
The operators complained that the motor would occasionally not respond to the pushbutton but it seemed random and might only last for one or two pushes of the button. It would then work properly for some time. One of the guys on another shift then mentioned that he had changed one of the fuses out a couple of times and that seemed to make the problem go away for awhile. This had been going on for some time before I had the opportunity to take a look at it.
The first time I was called for this I found that one of the poles of the fuse holder was lit indicating a blown fuse. However, the light did not look "right" to me, it seemed to be dimmer than I would expect. The really odd thing is that the motor was still operating normally, even though the fuse was showing blown. I shut the machine down and traced the circuit, finding a very old wirenut where the plastic cap had vibrated off exposing the coils in a conduit bodythat was very moist and rusty inside.
I replaced the conductors and cover on the conduit body (eliminating the splice) and have had no problems since. My theory is that the exposed wirenut was occasionally shorting to ground, causing the fuse to blow and that the motor was still drawing power through the indicator of the fuseholder. I wish I had experimented with this a little more before I repaired it but I needed to get the machine running again.
My co-worker says I'm full of @#$%. We don't see eye to eye on much, mainly due to, again putting it politely, the amount of motivation he shows and I really want some backup on this. Can anyone provide some insight on this? Am I crazy?
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