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Higher amperage in magnetically coupled motor pump

Higher amperage in magnetically coupled motor pump

Higher amperage in magnetically coupled motor pump

(OP)
Replaced a flex coupling on a 150 hp, 440V, 3 ph pump with a magnetic coupling. Motor controller now trips on 115% overload during startups. Magnetic coupling manufactured by Rexnord. how is the slip contributing to a higher and/or longer period of startup current?

RE: Higher amperage in magnetically coupled motor pump

The new one probably has much less slip than the replaced one. This causes the higher starting current.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Higher amperage in magnetically coupled motor pump

(OP)
The old coupling was flexible with no coupling slip

RE: Higher amperage in magnetically coupled motor pump

Ah! Then the new one could be heavier?  The inertia of the system has gone up.  A longer, higher current start.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Higher amperage in magnetically coupled motor pump

The added coupling slip (3%) is stretching out the time it takes to get the load to full speed, so the motor is working harder for longer. That is the definition of overload. Your motor was probably marginally sized to begin with, this may have exacerbated the problem.


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