Published:
11 September 2014
Category:
Q&A
Peter asks this question about the burning out of a motor wired in star-delta formation, and where to place overload protection in the circuit in future. It has been answered by ABB (Theme – Electrical Control):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: Recently, I had an electric motor burn out on our compressor. Upon inspection, I found that we were single-phasing the motor.
It's wired in star-delta form and there is no overload in line to protect the motor, so it carried on running until it caught fire, as it couldn't trip out!
My question is, where should the overload be, in the star or delta contactor (as I'm unsure as to where to put the overload).
I don't do much star delta and would appreciate some help via experts.
Answer: We normally put an overload in line with the main contactor in the star-delta starter, and size it at 0.58 x full load current (FLC) of the motor since, when in service, it shares the load with the delta contactor.
I have attached a typical wiring diagram (shown without the control circuit diagram) – please use the link below (PDF doc – 25kB file size).
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