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3 phase motors

MrJack96
I’ve got two questions regarding maintenance on motors. The first one is is there any hazards lubricating a motor in service I know obviously there will be mechanical safety to be aware of but electrical is there any issues. 


my second question is with motor overloads how bad for the motor is having a 1.8amp 10a overload on a motor with 1.75FLC I know it can still be overloaded by 50ma but is it a concern. 


thanks again guys!
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    MrJack96:

    I’ve got two questions regarding maintenance on motors. The first one is is there any hazards lubricating a motor in service I know obviously there will be mechanical safety to be aware of but electrical is there any issues. 


    my second question is with motor overloads how bad for the motor is having a 1.8amp 10a overload on a motor with 1.75FLC I know it can still be overloaded by 50ma but is it a concern. 


    thanks again guys! 


    Greasing motor bearings is an art and a science. There should be no problem in greasing the bearings in service, actually this may help to distribute the grease inside the bearing. Do not over grease though, as this creates friction and heat and may damage the bearing by grease degradation. Some bearings should only be filled to a thirty per cent capacity. It is essential to use the correct viscosity  grease. Slow shafts need a heavier grease than faster rotating shafts. Consult the manufacturers of the machines. There are some good Youtube videos covering machine and motor lubrication.


    Electric Motor Bearing Greasing and Lubrication (machinerylubrication.com)



    Z.


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    my second question is with motor overloads how bad for the motor is having a 1.8amp 10a overload on a motor with 1.75FLC I know it can still be overloaded by 50ma but is it a concern. 


    thanks again guys! 


    Such a small difference should do no harm. The motor may take many times F.L.C. at start up or under heavy loads for short periods.


    Z.


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    A very small overload on a motor will in practice be fine except uder otherwise adverse conditions. It is not amps as such that kills motors, but temperature rise.

    If a motor rated for 40 degrees ambient is slightly overloaded at 20 degrees it should be fine. If however it is designed for up to 40 degrees ambient, but then overloaded, even slightly at 50 degrees ambient, then it may have a reduced life.


    fluctuations in mains voltage or in mechanical load may result in the overload being a little more or a little less than expected. The actual tripping current of a thermal overload relay also varies due to manufacturing tolerances and the ambient temperature around the starter.


    For a new installation, I would consider it a poor design that permits of overloading a motor, fit a smaller overload relay, or a larger motor.

    For an existing installation that shows no signs of trouble I would be inclined to accept it.
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    And more on the lubrication issues....

    https://www.bing.com/videos/search?q=youtube+bearing+lubrication&docid=608016719548254206&mid=0DA2D178291


    Z.

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