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Motor Current?


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#1 honeywell

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Posted 24 February 2004 - 07:09 PM

I have a motor connected to a pump for low pressure hot water (62 dec c) on the data plate the motor says 400V 50Hz 1450 rpm 7.5Kw 0.82cos 15.20 amps delta connection. But when I connect my clamp on amp meter the current drawn is 18 amps why is this when the motor is rated at 15.20 amps is this rating not true power??

Thanks for any help


Paul Kav
Honeywell Controls

#2 grobert

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Posted 26 March 2004 - 09:39 PM

"current drawn is 18 amps why is this when the motor is rated at 15.20 amps


If this is the case, and you are sure that your amprobe is in proper working order, the motor is being overloaded.

Please remember if the input voltage is higher than the motor nameplate rating the current will be proportionately higher. You may not be over working the motor depending on it's service factor, however it sounds like you have a problem.

I would remove load from motor. I bet this will lower the amps below nameplate. Check to load for mechanical problems.

#3 marke

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Posted 26 March 2004 - 11:19 PM

QUOTE

Please remember if the input voltage is higher than the motor nameplate rating the current will be proportionately higher

If the motor is loaded, and the voltage is increased, the current will actually drop, not increase. You can treat the loaded motor as a roughly contstant power device provided that the shaft load does not change and the speed is constant. Increasing the voltage can however cause problems with increasing iron loss and resultant overheating.
Reducing the voltage will cause the loaded motor current to rise.
In the case of a completely unloaded motor, reduction in the voltage will reduce the current and increasing the voltage will increase the current.

I would suggest ensuring that the clamp meter is not being influenced by the magnetic filed from the motor. Repeat the measurement at the switchboard or starter and check for the same readings. If the motor operatied continuously with this overload, it would run hot and fail early.

Best regards,




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