Motor Inrush Current
Motor Inrush Current
(OP)
We have several in-house publications citing that an electric motor in-rush current should be 500% of rated current. Is this rule derived from some obscure agency specification I can't find or just someone's rule of thumb for a good design basis.





RE: Motor Inrush Current
Inrush is technically just the magnetizing current which could be much higher but very short lived.
The LRA is the inherent characteristic of a general purpose induction motor. It is not "required" by any standards but natural characteristic of the beast. For a 3 phase motor it is generally between 500% to 700% of its rated load current.
There are design aspects that can be tweaked to change the LRA somewhat, generally at expense of something else such as available torque, efficiency, etc. They are standardized (categorized) by NEMA code letters, A through V, which relate to the designated multipliers ranging from 3 to 22. Most common being the F, G and H (5, 6 and 7).
The starting current changes (reduces) with reduced voltage starting but at the expense of available torque.
Rafiq Bulsara
http://www.srengineersct.com
RE: Motor Inrush Current
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Bill
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