Motor Overload Protection

3 replies [Last post]
CodeBrad's picture
Joined: 2013-11-21

I have a question about the setting of an overload. We have several applications where the motor may have a SF of 1.37 or 1.4 (water pumping). The motor operates around 125% of FLA and will trip the overload after sometime of running since it is a continuous applicaiton. Is there anything in the Code that gives us some leeway to adjust this setting up just a little bit to account for the larger SF or is only 125% allowed?
Thanks in advance for any advice you can offer.

bmickler's picture
Joined: 2013-10-23

Brad, if your motor(s) are all above 1HP, and as you say are considered continuous duty, then 430.32 is the area in the Code that applies. The percentages shown at 430.32(A)(1) can be increased. 430.32(C) allows motors with a SF of 1.15 or greater to be set at 140% of the nameplate, if the 125% setting per 430.32(A)(1) is not sufficient to carry the load. If you still have some issues, you may want to look at using an integral, thermal protector, if available for your motors. That would give you another option, if needed. Hope this helps.

W A Werning's picture
Joined: 2014-02-12


I believe you were using Table 430.32(A)(1) since you mentioned 125%. Did you use nameplate ampacity?

According to 430.32(C), if the selected device calculated from that table [430.32(A)(1)] is not sufficient to start the motor or carry the load, higher size sensing is permitted and you can use Table 430.32(C) at 140% for SF 1.15 or greater and/or 40 degreeC or less.

This should do it if everything is properly sized elsewhere for the motor.


Note: Remember to use the motor nameplate ampacity, not the FLC. Yes, you may use T430.32(C)

USS Hornet's picture
Joined: 2015-01-07

USS Hornet

It sounds like you are operating your motors continuously at 25% overload. No wonder your overloads are tripping. What you need are larger motors, not resetting your relays. I'm surprised you haven't had a motor burn out yet.

Premium efficient motors may be suitable since your existing motors run for long periods of time. Size the motors so they are only loaded to 75-80% load. The efficiency at this loading will be the same as 100% loading. They will run cooler (temperature is extremely important) and they will be more able to tolerate temporary overloading, higher ambient temperatures and low voltage conditions.

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