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| Lots of times, electricians will use starters for three phase motors with only two heaters. If the phase that's gone or weak only causes high current in the phase without the heater, the motor will be sure to fry. That's most common when run from an open delta power source that guarantees unbalanced line currents. Open delta transformers sized too close to the motor rating make that worse and some utilities put too small a transformer on the wild leg making that all worse.
Then I've known electrical wholesalers when asked for the heaters for a particular motor current to look up the proper rating and then give the electrician heaters for two steps more current to prevent nuisance trips. But that leads to the "nuisance" of burned up motors without ever tripping the overloads.
Gerald J. | |
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grain bin with single phase power
