Thermal Protection Rating on small electric motors

I appreciate all the help and guidance. These recent answers have been clear and easy to understand. Hopefully this is my last question on small motors for a while (if not, I'll need more humor, but am willing to learn).
Can anyone educate me on "Thermal Protection" Rating on electric motors. Old motor is "AA", second motor canabalized from a friend's old spa is C1 (works well on low speed, but overheats in 30 minutes to an hour on high speed), Store recommended and purchased motor is "MA" and overheats even on low speed -- not good.
Tony & Ron, you got me to understand Insulation Class, Thanks, If someone can educate me on "thermal protection" ratings or point me in the right direction to look, I should hopefully know enough to take the new motor back (it appears undamaged, just gets warm after use and shuts itself off, electrical connections and windings look clean and new) and exchange for the correct motor. The salesman seemed clueless on these ratings and he is the "technical guy" for the store. By process of elimination, I'm guessing the ratings have something to do with why the motors are over-heating. I can't find an electric motor repair place in my area to take the motor in to so I am at the mercy of the spa store. I'd at least like to be knowledgable so I get the right motor.
The cord and control box are the other common links in the problem. When I moved the cord from the original motor to the others I examined it -- Condition look's good. Opened control box, some minor corrosion, from damp air over time but not sure what to check in here. Nothing looks badly damaged, overheated or burned. I did remove a moderate sized cobweb attached to one electrical component. If the next motor has problems I will have to suspect the control box. It seems easiest to try to get a new motor that matches the old on thermal protection (already matched all the other specs except minor difference on amps and 3.1 vs 3.5 as I understand it shouldn't matter, just means newer motor is more efficient, correct me if I'm wrong), but "has the rating terminology for thermal protection changed over the last ten to fifteen years" (best guess at age of original motor based on info on plate, hard to read). If someone can educate me I'll at least know what to look for in the way of thermal protection.
All the motors meet the specs you all explained for Insulation Class, and ambient temperature for where used (and match to the old motor). Thermal protection code on each is different.
Thanks in advance, Andy
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P.S. I'll try to match Amps exactly on the new motor, but am still concerned about the "thermal protection ratings".

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1_Patriotic_Guy wrote:

No, dont do that. Get a motor with the same HP, Voltage, RPM, Frame and Duty ratings. Forget about thermal protection ratings and amps. The amps will be lower on newer more efficient motors, thats a good thing. you dont need to go find a motor that draws more to match the old one. As people have been trying to tell you, the problem is in the load on the motor, the pump or something is loading the motor to heavy. You're trying to make a simple problem complex - it isnt. Eric
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1_Patriotic_Guy wrote:

Hi, Sounds like your motor is running too hot or under rated to do the job. Thermal protection is when motor gets too hot, the temp. sensing switch removes power from motor to keep it from burning out. It can happen when motor is under powered(not enough torque or Hp) or temp. is too high. Two types of sensors, one self resets when motor cools off, the other you have to push a button. Are you sure, the pump is OK? Like bearing is going out or something putting extra drag on the motor? Tony Tony
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Replacing these motors is not rocket science. The fact that you have replaced motors and they are not working has nothing to do with thermal protection, which is a symptom and not the problem. If you replaced it with the correct HP and speed, which any shop that sells spa parts should be able to provide, then the motor should work. There isn't anything particularly unique about these motors, the same one will fit many spas. Have you checked the voltage on the motor while it's running to make sure it's getting full voltage? And have you inspected the pump to make sure it's turning freely and not binding? Is the water flowing freely without obstruction? Those are the only things that will cause it to overheat.
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I tend to agree with Chet. The motors should be rated for continuous duty and would be stated on the nameplate. If they are rated for intermittent duty, then they are not suited for a spa.
I wouldn't be overly concerned about the ampere ratings on a new motor compared to an older motor. The new motors are more efficient and have less "Losses" then older motors. As long as FRAME, VOLTAGE, HP, RPM, and DUTY are the same the motor should operate correctly.
Low voltage or too much of a workload will cause a motor to overheat. Have you been using the same pump or did you get a new one? I hope that you are not running the pump while it is dry.
The control box may be your problem. The contacts on the motor relay(s) may be corroded and causing a lot of resistance to be in the motor feed and consequently a low voltage condition. Try running the motor directly off of an extension cord (One rated for the load) and see if it overheats.
John Grabowski http://www.mrelectrician.tv

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I'd love to plug the pump into a standard 110 volt exension cord to try that but the plug isn't a standard plug (no it's not a 220V plug) but it does have 4 prongs which match to the outlet on the control box. I can wire the pump to a standard plug if that is safe? But obviously could only connect low speed or high, but not both due to being 1 wire short with a standard plug -- This is why I was asking about how the 2 different speeds are powered, e.g. is voltage only on the black wire when operating on high -- I guess I can test this if it is safe to run without water for 30 seconds or so. Patiently awaiting a reply, Andy

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