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Thread: IEC versus NEMA

  1. #1
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    IEC versus NEMA

    I’m encountering IEC equipment more and more, but I have no clue what the real differences are. I know that IEC is a European standard and NEMA is an American standard, but that’s it. I know that IEC stuff is known to be smaller, but is it less durable? Could anyone suggest some reading?

  2. #2
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    Just as the computer your are working on now is smaller than the ones 20 years ago, the IEC contactors are phyiscally smaller.

    A rule of thumb I use:

    Always size the IEC contactor for the maximum amp rating that the equavalent NEMA contactor max amp rating. the IEC will still be smaller but have higher capacity than the exact amp rated IEC contactor will be able to handle. Also verify if the IEC is rated to break the running load of the motor, Type 3 versus type 1. Type 1 is for holding current, not breaking current.

    Hope this helps.
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  3. #3
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    Main difference:
    IEC is performance based, NEMA is manufacturing based.

    What this means:
    With IEC, you can build it anyway you want too as long as it passes the tests. NEMA on the other hand, basically says that if you build it a certain way, it will perform a certain way.

    MORE IMPORTANT:
    Short circuit calculations for IEC are based on IEC 60909, which is the European methods, versus IEEE short circuit calculations. The impact is dramatic, and the short circuit numbers from the analysis mean completely different things. Therefore, you CAN NOT, and I will repeat, you CAN NOT use equipment with an IEC rating in place of NEMA rated equipment unless it has a dual rating. There is not a "factor' that can be applied to go from one to the other. Many IEEE papers have been written dispelling this myth.

    A few years back, there was a fuse manufacturer going around and showing people, by use of a video, that the IEC equipment was cheap, and could not withstand the same fault current as NEMA equipment and that's why you needed to use fuses in place of a breaker.

    The fact was, that they were showing you e.g. a motor starter that had say a 65kA rating in IEC, and a 65kA NEMA starter and the IEC equipment was destructing. The reason, 65kA in IEC does not mean the same as 65kA in NEMA.

    More and more manufacturers are coming out with dual rating equipment. Many manufacturers, for example Schneider Electric a.k.a Square D, bought companies so they could specifically offer both lines. GE did the same thing. But the bottom line, is that if doesn't have a NEMA rating, it should not be UL approved, and therefore you should stay clear.
    "Just because you're paranoid, doesn't mean they're not out to get you"

  4. #4
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    Quote Originally Posted by boater bill
    Just as the computer your are working on now is smaller than the ones 20 years ago, the IEC contactors are phyiscally smaller.

    A rule of thumb I use:

    Always size the IEC contactor for the maximum amp rating that the equavalent NEMA contactor max amp rating. the IEC will still be smaller but have higher capacity than the exact amp rated IEC contactor will be able to handle. Also verify if the IEC is rated to break the running load of the motor, Type 3 versus type 1. Type 1 is for holding current, not breaking current.

    Hope this helps.
    I would have to disagree. IEC contactors come in many many more sizes, and therfore the range is much tighter. As far as physically smaller, it has partly to do with the way IEC calculates the fault current. The 60909 method uses a decay, and therefore the current actually seen by the contacts is less then what IEEE would calculate. Unfortunately there are no cross references that allow you to switch between the equipment. You would need to run the proper analysis IEC or IEEE to determine the properly rated size, or always use at least dual rated equipment.
    "Just because you're paranoid, doesn't mean they're not out to get you"

  5. #5
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    Quote Originally Posted by 831
    I’m encountering IEC equipment more and more, but I have no clue what the real differences are. I know that IEC is a European standard and NEMA is an American standard, but that’s it. I know that IEC stuff is known to be smaller, but is it less durable? Could anyone suggest some reading?
    There are different answers for this question based on what type of product you are looking at.

    IEC starters and contactors can be tested to the same UL HP ratings and operations standards as NEMA devices. The IEC wiring terminals are designed to be used with a minimum of 75C wire so they are smaller and run hotter than NEMA devices which are rated for 60C. IEC contactors are typically rated closely to UL HP values while NEMA devices are based on old automotive sizes which allowed "no thought" applications (a UL Listed IEC 10HP 480V contactor may be rated for 18A continuous while the equivalent NEMA Size 1 device is rated for 27A). But smaller does not always mean less durable (look at an HVAC contactor).

    Comparing electical enclosures is a bit more complicated. Among other things UL/NEMA requires strength (i.e. thickness of materials) and IEC may not.

    Personally I have no problem using IEC contactors. If I want equivalent performance I chose them based on continuous amps not just HP.
    Just because you can, doesn't mean you should.

  6. #6
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    Quote Originally Posted by kingpb
    But the bottom line, is that if doesn't have a NEMA rating, it should not be UL approved, and therefore you should stay clear.
    So are you saying the voluntary NEMA standards are more important than "certified" third party (i.e. UL) testing?

    The fact is, an IEC device may have a UL tested fault rating even though it does not meet NEMA standards.
    Just because you can, doesn't mean you should.

  7. #7
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    A few years back, there was a fuse manufacturer going around and showing people, by use of a video, that the IEC equipment was cheap, and could not withstand the same fault current as NEMA equipment and that's why you needed to use fuses in place of a breaker
    http://www.bussmann.com/apen/pubs/NoDamage.asp
    NEMA has a withstand / SCCR (stand-alone) of 10k amps usually, and you size it to FLA of the motor. Contacts and overloads are accesable & replaceable
    IEC has a withstand / SCCR (stand-alone) of 5k amps, and you size it to the amount of total actuations. Contacts & overloads are not accesable or relaceable and are considered "throw-a-way". I have heard that AB now has replaceable contacts.
    With both NEMA and IEC, there are "Type-2" coordinations, with "No-damage" UL listings. Type 2 Coordinations come from the IEC world of 60204-1, adopted by NFPA-79.
    and is now in the NEC under article 670.
    Just my $.02
    Last edited by davidr43229; 04-09-07 at 06:17 PM.
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  8. #8
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    Quote Originally Posted by 831
    I’m encountering IEC equipment more and more, but I have no clue what the real differences are. I know that IEC is a European standard and NEMA is an American standard, but that’s it. I know that IEC stuff is known to be smaller, but is it less durable? Could anyone suggest some reading?
    In addition to what others have said, usual overloads used with NEMA products are class 20, usual with IEC are class 10. Be aware of that if your motors are hard to start. In our opinion, the IEC frame motors were better protected by the class 10's; in addition, many incorporated thermocouples, a rarity to us at the time in smaller NEMA frame motors (our applications were normally 10HP and smaller). We experienced some nuisance tripping of IEC class 10 overloads starting NEMA motors that didn't occur with class 20 overloads, and which didn't APPEAR to overheat the motors.

    Far ago and long away, we found that NEMA contactor ratings applied to plugging, reversing, and inching service. We found that IEC devices had to be oversized at least one size, often 2, to operate well in that environment.

    We found that IEC contactors worked well at their rating MOST of the time, at lower cost, and at lower panel cost, because of smaller size. When we needed plugging and inching, we usually used NEMA rather than IEC. We used class 20 or class 30 overloads if we were plugging/inching.

  9. #9
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    Iec

    my experience mirrors GeorgeB's.
    I might add, from my experience, that unless you carefully select you short-circuit/ground fault protection ahead of the IEC components you will find a higher ration of welded contacts and "self-destructed" units than you would find with comparable NEMA components.

  10. #10
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    For my two cents. I think the terminal blocks are a pain in the tushie, either my eyes are failing or the terminatal blocks are sized for pure frustration, as far as the contactors, when you take them apart the contacts just do not appear to by as substantial as a simialr sized NEMA contactor.
    Brian John
    Leesburg, VA

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