Motor short circuit and overload protection

[m sleem]

Can we use adjustable MCP for overload and short circuit motor protection?

 

[Sajid khan]

Can we use adjustable MCP for overload and short circuit motor protection?

I think, this will answer your question.

http://apps.geindustrial.com/publibrary/checkout/DER-019?TNR=Application and Technical|DER-019|PDF

 

[m sleem]

I will rephrase the question,

Is it mandatory as per NEC to use separate o.l for motor protection or the adjustable MCP Can do the job for short circuit and overload protection?

 

[Abdel Rahman Mohamed]

I think adjustable MCP is better so it could be adjusted with different conditions force the motor to draw more current.

 

[augie47]

I will rephrase the question,

Is it mandatory as per NEC to use separate o.l for motor protection or the adjustable MCP Can do the job for short circuit and overload protection?

430.42 does not include MCPs as an approved overload device.

 

[don_resqcapt19]

An MCP is an instantaneous (magnetic) only device. It cannot provide overload protection as it does not have a long time trip function.

 

[Sajid khan]

An MCP is an instantaneous (magnetic) only device. It cannot provide overload protection as it does not have a long time trip function.

Instantaneous-trip circuit breakers are circuit breakers that have a magnetic trip function but not a thermal trip function. They are designed for one very specific purpose, that being to provide branch-circuit short-circuit protection for motor circuits. The NEC permits their use only in listed combination motor controllers per 430.52 (3).

 

[Sajid khan]

I will rephrase the question,

Is it mandatory as per NEC to use separate o.l for motor protection or the adjustable MCP Can do the job for short circuit and overload protection?

According to table 430.52 both options are available i.e instantaneous trip breaker (magnetic only) and Inverse time breaker (magnetic + overload). IMO, to do both functions (sht ckt +overload) in one breaker you have to choose Inverse time breaker.

 

[m sleem]

An MCP is an instantaneous (magnetic) only device. It cannot provide overload protection as it does not have a long time trip function.

So that, any breaker provide LSI trip (long, short, instantaneous) would qualify and meet NEC requirements & no need of having separate overload protection.

 

[Dennis Alwon]

I have never seen any substantial motor that could be run without overload protection. Overload protection is very different that short circuit and ground fault protection which, I believe, is what you get from an overcurrent protective device.

 

[Abdel Rahman Mohamed]

I have never seen any substantial motor that could be run without overload protection. Overload protection is very different that short circuit and ground fault protection which, I believe, is what you get from an overcurrent protective device.

what i understand from your reply that MCP with overload protection cannot do the job and protect the motor from overload.correct me if i am wrong. :?

 

[gray.one]

Schneider's NW breakers have overload and short circuit protection combined in their trip unit


Sent from my iPhone using Tapatalk

 

[don_resqcapt19]

So that, any breaker provide LSI trip (long, short, instantaneous) would qualify and meet NEC requirements & no need of having separate overload protection.

No. A thermal magnetic breaker sized large enough to permit the motor to start will be too large to provide overload protection. Also assuming the motor is over one horsepower, a breaker is not one the overload devices that are permitted by 430.32(A).