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Tips/Techniques Thermal overload relay

Tips/Techniques
Working on setting up my diy phase converter. Legs are balanced. Pony runs smooth. The issue I am tracking down is the thermal overload relay tripping. It now takes about 3 mins to trip and cut power to the machines and used to trip out in 30 seconds or less.

I will assume the relay is stock. It only adjusts to 4amps but motor FLA is 6.5 amps. I do not own a clamp on meter yet but may have to buy one. The motor is 3 phase and claims 2kw but says HP so either 2 or 2.5 hp. Pony is 5hp.

Should the thermal overload relay not be sized bigger? Does anyone know running amps of a 2hp 3phase motor not under full load? This lathe came from a school and I did find loose wiring in some spots. Could this be wiring gremlins? The twist lock plus seems kinda loose and wonder is current loss could be there?
 

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CEC 28-306 Rating or trip selection of overload devices

...if of the adjustable type, shall be set to trip at not more than the following:

a) 125% of the full load current rating of a motor having a marked service factor of 1.15 or greater; or

b) 115% of the full load current rating of a motor that does not have a marked service factor or where the marked service factor is less than 1.15.
 
The one caveat to Rule 28-306 is found in Appendix B of the CEC:

The manufacturer's instructions should be consulted to determine how to match the trip setting or rating information to the full load current rating.
 
Here’s the data sheet for a typical Baldor 2HP 230/460 3-ph motor. Full load rating is 5.6A @ 230 volts. The bottom chart is for 460 volt, double the current draw for 230 volt.

IMG_0051.jpeg
 
In the example @whydontu gave, the manufacturer already gives the S.F. (service factor) amps to be used for determining the overload settings at each voltage.

S.F. = FLA @ 230 V = 5.6 = 6.3/5.6 = 1.125 <- so this specific motor's S.F. is 1.125 vs 1.25 or 1.15.


@Hollow-Grind

If your motor's nameplate doesn't give the already calculated S.F. Amps then you would follow the CEC rule as shown above to determine the overload setting.
 
I will assume the relay is stock. It only adjusts to 4amps but motor FLA is 6.5 amps. I do not own a clamp on meter yet but may have to buy one. The motor is 3 phase and claims 2kw but says HP so either 2 or 2.5 hp. Pony is 5hp.

Follow what elektrishun has posted. AS you can not adjust to that level then you will likely need a new overload and make sure that the contactor can also handle the increase in current.

If your building this type of project it is a good idea to borrow or buy a decent clamp on meter as you may have a high leg or some other anomalies in your build.
This is the one I recommend to my budget minded apprentices. https://www.homedepot.ca/product/kl...r-ac-auto-ranging-400amp-with-temp/1001545933
 
Thanks for all the advice. It just bothers me that this was probly designed to work the way it is and I can’t make it yet. I will buy a clamp on meter to test with. Rona plus has a Fluke for half price 🙂


Pic of lathe motor name plate for reference.
 

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Bought a cheap clamp on Fluke meter and it arrived today. Should have bought one sooner. I’ve played with caps but can’t get the amps down. Best I can do is T1 5.1 amps, T2 4.9 amps and ghost leg 4.2 amps. Voltages under lathe load are T1-Ghost 235, T2-Ghost 245, T1-T2 244

Adding caps just up’s the amp load. Currently I only have 70 and 35 UF caps to play with. Still well under the 6.5 FLA nameplate of the lathe motor but over the 4 amp thermal overload.

Not throwing in the towel yet…
 
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