Thermal overload connection of motors

[StewG]

At my mfg plant, a number of our blowers we make (up to 60 hp) are returned for repair or replacement of motors which have failed in one way or another. In many cases, it seems that thermal overloads in the motors were never connected into the motor control systems. I would have thought that a properly engineered system, this would be part of the wiring diagram/schematics. Are these devices just not used, or are they not used in lieu of overload heaters? Or is this just not understood in general even though they are clearly marked on the lid of the terminal boxes.

 

[mcclary's electrical]

At my mfg plant, a number of our blowers we make (up to 60 hp) are returned for repair or replacement of motors which have failed in one way or another. In many cases, it seems that thermal overloads in the motors were never connected into the motor control systems. I would have thought that a properly engineered system, this would be part of the wiring diagram/schematics. Are these devices just not used, or are they not used in lieu of overload heaters? Or is this just not understood in general even though they are clearly marked on the lid of the terminal boxes.

The original motor may not have had the internal thermistor. In comes a replacement with two extra leads and nowhere to land them. It happens alot.

If it's not on the plans, no electrician is gonna run the extra wires needed to incorporate those contacts into the electrical plan.

You can incorporate them into your existing scheme rather easily

 

[weressl]

At my mfg plant, a number of our blowers we make (up to 60 hp) are returned for repair or replacement of motors which have failed in one way or another. In many cases, it seems that thermal overloads in the motors were never connected into the motor control systems. I would have thought that a properly engineered system, this would be part of the wiring diagram/schematics. Are these devices just not used, or are they not used in lieu of overload heaters? Or is this just not understood in general even though they are clearly marked on the lid of the terminal boxes.

Hmmm... Klixons are not often seen on those sizes, unless they are Class I/II/III, Div. 1 rated XP motors. In that case it is MANDATORY to use them in ADDITION to the separate overload element required per Art. 430.

The ASD applications to motors that are not suitable for them or thge misapplication of the same is probably the most common cause of early motor failure. (I presume that is the case since you are the manufacturer of the blowers and that is why they returning them to you.) Could it be that your blanket supplier is the low-bid offshore motor manufacturer?

 

[augie47]

Other than the XP motors Mr. Weress mentions, my experience has been that few electricians see internal thermal protection. By habit, most rely on thermal or electronic units inherent with the starter.
I'd say you are fighting lack of knowledge, resistance to installing control wiring not already present (as McClary mentioned) or the age old "it was good enough for years" attitude.

 

[StewG]

While we are beginning to transition to offshore motors, we have been using the Ft. Smith Arkansas and its assorted plants. We have had more issues with bearing to bearing and shaft dimensions than anything electrical. When I asked them for an officially published tech sheet, they really didn't seem to come up with much for connecting the thermals. It is really a very simple thing to connect, it just seems no one bothers. I have no idea where I learned it.