Breaker for motor
- Thread starter mannyb
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jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
Using T430.250 for a FLA of 40A and T403.52 for a max of 250%, the breaker would be a max size of 100A for a standard inverse time breaker.
I appreciate the answer. If I were to use a breaker with magnetic trips would the 100a be the same? I always assume thE wire size wouldn't handle that higher amperage breaker if something happened to wiring which is why I lack confidence with breaker being larger thaN wire Thanks again.
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- Occupation
- Licensed Electrician
430.52 is about sizing for ground fault and short circuit protection, which when that happens the amperage goes from thirty amps up to three hundred thousand amps and trips the breaker, so wire size by table 430.250 is not going to be a problem. If it were we would have to size all our wires at locked rotor amps.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
What ActionMan said and see 430.52(C)(3).
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
You can’t use a mag-only breaker on your own anyway, they can only be used as part of a listed assembly like a combo motor starter. In that case, the OL relay protects the wires, so the mag-only breaker can be whatever size is needed to get the mag trips that follow the applicable rules.
Please let me know where i am wrong. If I size the motor per discussion and use the 100a with thermmag trips for motor starter combo What type breaker can i use panel for feeder circuit to combination starter? Would I need to 100a breakers same type. I have done starters, motors, and start/stops in a while and the more i discuss its coming back but I do struggle with this a bit.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Is the motor the only thing on this feeder? If so, the same rules apply.
Yes only thing on feeder. What I need 2 breaker one for feeder and one for starter?
- Location
- Illinois
- Occupation
- retired electrician
You need a breaker at the supply end of the conductors and you need a disconnect within sight from the motor controller (starter). In some cases the breaker at the panel can satisfy both requirements.
The controller is inside a control panel with the typical on or off switch hamdle. Would that qualify as disconnect? I'm not trying to get away without doing it right way but I am trying to be not to cost customer alot of money.
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The real problem as to why so may questions about motors. I need a 100a breaker. The panel is 1200a siemens 480 3p panel. The current installation has fuses for motor controller. The customer wants a breaker not fuses. Siemens doesn't make 100a for motor protection and no one carries 100a only 150a . The 150a in Odessa Tx is $3600. Per our conversation I need 2. Thats my situation. If you guys have any suggestions please let me know.
- Location
- Illinois
- Occupation
- retired electrician
You don't use any kind of special breaker. Just a standard thermal magnetic breaker at the supply end of the conductors that feed the motor controller.
If the control panel switch turns off the actual power to the motor controller, that can serve as the required within sight controller disconnect.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If you have a feeder breaker in the switchboard that is feeding nothing but that motor starter, you do not need another breaker or fuses at the motor starter, but you may need a disconnect switch. But non-fused disconnects have very low SCCR values, ie 10kA, and most industrial applications will have more than that available. Since you cannot retrofit with an MCP (legally), a Thermal-mag Breaker would be easier.
After this question this subject will end BUT What if I wanted to use fuses instead breaker at motor starter. I would just use T430.52 for fuses and If I used breaker I would only need the breaker to be thermo mag if I wanted to use breaker starter?
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