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Siemens AG
Entry type: FAQ, Entry ID: 30550697, Entry date: 07/28/2008
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Difference Between Overcurrent Protection and Overload Protection

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QUESTION:  

What is the difference between overcurrent protection and overload protection?
 

ANSWER:

Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. It generally operates instantly. Short circuit is a type of overcurrent. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection.

Overload protection is a protection against a running overcurrent that would cause overheating of the protected equipment. Hence, an overload is also type of overcurrent. Overload protection typically operates on an inverse time curve where the tripping time becomes less as the current increases. Overload relays as well as “slow blow” fuses are commonly used to provide overload protection.

Some devices provide both overcurrent and overload protection. A thermal-magnetic circuit breaker has both thermal (overload) and magnetic (overcurrent) elements. Both elements operate as described above. Likewise the dual element fuse has both instantaneous and inverse time characteristics in the same fuse providing both overcurrent and overload protection.

 

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