Contactor Current Breaking rating
Contactor Current Breaking rating
(OP)
Can any one tell me if NEMA specifies the current breaking rating of NEMA rated magnetic LV contactors?
IEC has very specific utilization categories and the Life cycle tests specify both making & breaking currents & power factors. IEEE 242-2001 in Sec 10.4.1.4 says that " NEMA rated magnetic contactors are tested to break up to 10 times the full load current..."
In my opinion a min. value should be enforced by NEMA and then manufacturer's are free to equal or exceed these values and then publish them.
IEC has very specific utilization categories and the Life cycle tests specify both making & breaking currents & power factors. IEEE 242-2001 in Sec 10.4.1.4 says that " NEMA rated magnetic contactors are tested to break up to 10 times the full load current..."
In my opinion a min. value should be enforced by NEMA and then manufacturer's are free to equal or exceed these values and then publish them.






RE: Contactor Current Breaking rating
In general, a NEMA contactor will be much bigger than an IEC contactor for the same horsepower rating.
RE: Contactor Current Breaking rating
My specific problem is : We are setting our MCP instantaneous setting pretty high since we have premium efiiciency motors having high first cycle inrush. This means that the contactor will be asked to interrupt much higher currents viz. 15-17 times the FLA of the motor. IEEE 242-2001 in Sec 10.4.1.4 Page 354 cautions the user for such a situation and asks for validation of the contactor breaking rating; hence the question...
RE: Contactor Current Breaking rating
The NEMA approach to motor contactors is vastly different from IEC. The NEMA approach is to make contactors "application-forgiving" - the brute force approach.
Going from memory, I don't believe NEMA requires any specific performance testing from manufacturers to verify the contactor meets the life-expectancy requirements in the standards. I'm sure some testing is done, but I've never seen any published data from manufacturers.
Some new contactors carry both NEMA and IEC listings, IIRC. So that might give you a point of comparison.
RE: Contactor Current Breaking rating
But UL on the other had IS a testing and listing authority and there are indeed specifications to which UL tests devices for making and breaking capacity, in this case UL508C. For any manufacturer, those test reports are available. You may not be able to get them from UL, but you can insist that the manufacturer provide them to you, they are going to have them somewhere. If they say they don't or can't share them, don't use their products because they likely have something to hide.
Secondly, I have a small problem with the following (emphasis added): When you are specifying the instantaneous short circuit trip settings of a magnetic only CB, the CONTACTOR is not going to be doing the interrupting! The BREAKER will clear the fault, the contactor will not open up until after the power is cut off from the coil. In fact, if the coil power source is not fed from the load side of said breaker, it may never open up.
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RE: Contactor Current Breaking rating