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Unread June 24th, 2019, 09:14 PM   #1
kalabdel
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Troubleshooting single phase motor intermittent tripping breaker

Good day everyone,


Single phase motor,3/4 Hp, capacitor start, dual voltage wired for 115VAC with Allen Bradley reversing contactors and 10 amp circuit breaker. It runs a machine via V-belt and very simple mechanics.


It intermittently(could be weeks) trips the breaker and after resetting the breaker everything works fine for days and often weeks.



I have two such cases on two different sites and one customer provided specific information regarding their motor (the machine is two months old/new) that it tripped after having moved for a 7-8 seconds. Not on start-up. And I can eliminated the possibility of mechanical cause.



I've had similar problems over the years and always were resolved after a few trips by replacing the motors but would love a more knowledgeable approach to troubleshooting.


  • What tests can I perform on the motor?
  • If the centrifugal switch does not open after the motor reaches the required speed what happens, how is the motor, capacitor, winding etc. affected?
  • I removed the capacitor cover and the capacitor looked quite good but there was a very thin layer of red dust sort of like rust that was inside the cover and also on the part of the motor that was covered by the capacitor cover. Could this have come from inside the motor though the 1/2" hole the capacitor wire go through? If yes what would it be?
Thanks
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Unread June 24th, 2019, 09:30 PM   #2
duckman
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If the centrifugal switch doesn't throw out, the start winding stays in the circuit so both run and start are pulling current, so that is a very likely cause of the over current.
You should hear the switch click back in place when the motor slows and when after getting up to speed.
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Unread June 24th, 2019, 09:41 PM   #3
kalabdel
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Thaks ducman. How long would you say it would run without the switch opening before tripping the breaker? I think the motor draws 8 Amps and the breaker is 10 Amps.
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Unread June 24th, 2019, 09:45 PM   #4
Cow
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Your breaker is undersized. Who determined it needed a 10 amp?

Down here in the states, the NEC considers that a 13.8 amp motor at 115 volts.

We'd probably try it on a 20 amp breaker first, with the option to take it up to a 35 amp breaker if necessary due to starting issues. The NEC would even allows us to go even higher if it still had trouble starting.
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Unread June 24th, 2019, 09:48 PM   #5
kalabdel
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The manufacturer of the equipment. It's was bought and installed as is about two months ago. I will contact them in the morning and ask that question.
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Unread June 24th, 2019, 11:01 PM   #6
kalabdel
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Sorry, my mistake. the motor is 1/2 Hp.
Attached Files
File Type: pdf motor.pdf (46.9 KB, 8 views)

Last edited by kalabdel; June 24th, 2019 at 11:25 PM.
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Unread June 25th, 2019, 02:38 AM   #7
BryanG
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Unless you get some data you are just guessing. Connect a logger to the system that will store current and preferably voltage against time, sampling maybe every second. You can buy off the shelf units, or you can make your own with a spare PLC. Better still if you could trigger the logging as the motor starts, then you could grab the data with a higher frequency and not run out of storage.
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Unread June 25th, 2019, 06:16 AM   #8
EICS
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not sure about North American electrics but in Australia the standard curve Breaker is a C Curve for general Applications, for Motor starting a D Curve Breaker is recommended as it has a longer time delay curve for motor starting applications.



the Breaker is designed to protect the Cable so it should be sized for this NOT the Motor, the motor is protected by a Thermal (or Electronic) Overload.


check if its a Motor Starting Breaker as if its a general purpose that could be you intermittant tripping issue.
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Unread June 25th, 2019, 08:00 PM   #9
kalabdel
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Quote:
Originally Posted by BryanG View Post
Unless you get some data you are just guessing. Connect a logger to the system that will store current and preferably voltage against time, sampling maybe every second. You can buy off the shelf units, or you can make your own with a spare PLC. Better still if you could trigger the logging as the motor starts, then you could grab the data with a higher frequency and not run out of storage.

Thanks Bryan it sounds like a good project. I've been thinking of something of that sort and prefer your latter suggestion with PLC just need to make it as compact as possible and versatile to reuse with similar issues.
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Unread June 25th, 2019, 08:08 PM   #10
kalabdel
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Quote:
Originally Posted by EICS View Post



check if its a Motor Starting Breaker as if its a general purpose that could be you intermittant tripping issue.

Thanks EICS. I posted a link to the datasheet in my first post and it is general purpose for sure.


From the datasheet;
"The CLB-Series is a compact, single pole, push-to-reset family of thermal circuit breakers designed to protect
equipment. Utilizing simple, precision design with few moving parts, these breakers offer cost effective,
extremely reliable circuit protection with high resistance against shock and vibration."
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