low voltage induction motor protection
low voltage induction motor protection
(OP)
What is the difference between using the Motor Circuit Protector (MCP) versus using the Molded Case Circuit Breaker (MCCB) for LV motor protection?. Are there any conditions for use of either option?.
Thank you.
Thank you.





RE: low voltage induction motor protection
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RE: low voltage induction motor protection
1) Cost. Since an OL relay is going to be there anyway, the MCP need only have magnetic trips and when using 10's of thousands per year, the small difference in cost adds up.
2) Adjustability. In the past, the lowest cost MCCBs had fixed magnetic trips (Instantaneous Trip or IT), usually at a value between 250 and 400% of rated current, in addition to the fixed Thermal trips (I2t). In some motor starter applications however, this ends up being too low to avoid nuisance tripping and required using unnecessarilly higher Thermal current rated breakers. For example if you have a 75HP motor with 100 FLA, you could use a 150A TM MCCB, but if it had fixed mag trips set for 250% of 150A, that is only 375A, and the starting current of that motor could be as high as 600A. So you would have to increase the TM MCCB size to 250A in order to accommodate it.
Since the NEC will allow the IT settings to be as high as 1300% if necessary, MCPs provide a way of having settings that could be adjusted much higher than would be acceptable in any other application. But many MCCBs are available now with adjustable magnetic trips even if the thermal trips are fixed, so this feature is not as important as it once was.
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RE: low voltage induction motor protection
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