What would be the target relative humidity inside an electric motor storage facility? Approx. 5000 sq ft. Long term storage for 50hp. to 3500hp motors.

Are you gonna have the space heaters powered up?
Are you gonna have oil/grease in the bearings (& periodically rotate)?
If yes to both of above, certainly humidity control is much less critical.

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We do have heaters for this facility in the Winter and will be adding air conditioning very soon. We are in the deep South where the humidity can be very high. Being that you brought up oil and grease, we are also storing other rotating equipment such as gearboxes, large hydraulic gear pumps, rotory feeders ect... We do have a program set up to rotate this equipment monthly. Also we are in the process of filling the gearboxes to the top with oil to eliminate and air space to reduce the possibility of condensate forming in the empty head space. I guess my question is with these practices in place, how much attention should we give to relitive humidity?

How about the motor space heaters... will they be powered up during storage ?

I think you should have one of the following:

space heaters energized
or
motors wrapped and stored with dessicant
or
Class A controlled climate storage environment per ANSI N45.2.6 (a nuclear standard). I'm not sure exactly what the specs are for that but it has limitations on humidity and temperature.

The above is based on my interpretation of EPRI 1009698 - "Shipping and Storage of Electric Motors"

I remember there is also some detailed guidance for motor storage in EASA's "Large Electric Motor Handbook", but I don't have mine handy.

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