Contactor Current Breaking rating

[cherry2000]

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.

 

[dpc]

Well, 10 times rated load current is pretty specific, since the contactors are rated up to a certain maximum horsepower and maximum motor FLA. I'm not sure what you are complaining about. I don't have the NEMA standards in front of me, but they give a maximum motor FLA rating for each size contactor

In general, a NEMA contactor will be much bigger than an IEC contactor for the same horsepower rating.

 

[cherry2000]

Many of the NEMA manufacturer's do not publish the breaking current data for their magnetic contactors. In contrast, in IEC, there are very specific utilization categories, which give precise values for make & break ratings. Now NEMA ICS 2-2000 clearly mentions in Sec 8.1, : "..shall be 10 times the rated full load current for 10 operations..". A little later it says :"Ten times MFLCis not a rating " !!! Now the life of the contactor itself is not very clear at 10 times the current.
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...

 

[dpc]

If you like the IEC specs, then buy IEC contactors. I've never heard of anyone with a real-world issue related to the make/break capability of a NEMA contactor used for motor control, even on energy-efficient motors. I know many of instances of problems with IEC contactors due to misapplication of the lighter duty units.

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.

 

[jraef]

First off, NEMA cannot "enforce" anything. They are not a testing authority, they are a manufacturer's organization, more like the BPFOAEPP (Benevolent Protective Fraternal Order of American Electrical Parts Producers), but that probably was too long of an acronym. So although they publish standards to which manufacturers SHOULD conform, and most if not all do, there is no methodology inherent in the process to enforce that. Compliance is essentially voluntary.

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):

We are setting our MCP instantaneous setting pretty high since we have premium efiiciency(sp) 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.

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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[cherry2000]

jreaf..you are absolutely right regarding the role of NEMA & UL. I have to check the certifications and ask the correct questions to the vendor. Regarding your last comment, I am not very clear. The concern is for high impedence faults where the Fault level falls down to a value LESS than the instantaneous setting of the Motor circuit protector. Here, the only protection available is our humble Class 20 relay which will ask the contactor to open ones the trip time is over.As said earlier, 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.