Thread Starter

Martin Lowe

Although I understand the benefits of NEMA panel control gear (contactors, overloads etc.), it still has the apperance of something befitting a museum rather than a tech piece of equipment and costs a lot of space. Is NEMA control gear on it's last legs and about to rollover to the more integrated IEC control or is it here to stay?
IME, you need to upsize your IEC gear from the nameplate rating if you want a reasonable life. IEC contactors are designed with a finite life in mind. Nema does take up panel space, and its not always in a nice cubic package, but it is far from being on its last leg.

Bob Peterson

An interesting question. It seems more and more people are going the IEC route because of the cost savings involved. But, most of the automotive world seems to prefer the NEMA stuff because it lasts forever. My guess is that the NEMA stuff will be around for a while, but the IEC stuff will garner more and more of the market share until the market size is such that it is no
longer practical to supply NEMA stuff because the demand is so low.

My guess is this could take 20 years or more, but thats just a guess.

Bob Peterson

Steve Myres, PE

I agree with T. Connolly. The basic difference is that the NEMA stuff is rated MUCH more conservatively than the IEC stuff. This will translate into greater life, especially when switching frequently. I've found that the IEC components survive well, if you derate them significantly during engineering. Even after doing this, the IEC units are usually cheaper and take less space, as well as having a better selection of accessories.
Another difference is that typically the IEC stuff comes from the factory in little pieces and you have to assemble it, whereas much of the NEMA
equipment (switches and lamps in particular) comes assembled to a catalog configuration and you just mount it and wire it. At least, that was the reason that my electricians gave (at my last job) when they professed dislike for IEC components and preference for NEMA. I think that in many cases today, that's no longer valid- vendors will work with you to deliver configured components, and AB sells an IEC line that has as many little pieces as, say, IDEC.

That said, I often use IEC stuff because of the configurability and because it is cheaper and better looking. I have always thought that on ratings, the IEC stuff is rated for use just barely up to the current/duty cycle speced- especially definite purpose rated equipment- whereas NEMA is either conservative or the rated duty cycles are so extreme that most of us never
approach them and thus the "lasts forever" factor comes into play for NEMA equipment. It is also beefier (due to the conservative ratings?) and so in plant use, it doesn't fracture when an electrician cranks onto the terminal screws, mounting rings or whatever with the biggest screwdriver or pliers they can fit. Again, that's why some of the electricians I've worked with
prefer NEMA.

Other thoughts/stories/ramblings? <g>

Paul T

Steve Myres, PE

I hope you're talking about starters when you say IEC stuff is better looking than NEMA stuff. If you're referring to the pushbuttons and disconnects, I'll think we may have to schedule you a short visit at Bellevue! The IEC pushbuttons and disconnects look sleazy and cheap to me, and experience with them has borne out my fist impression. I think for durability, as well as fit and finish, you just can't beat Allen-Bradley NEMA pilot devices and disconnects. On contactors, I tend to concur, if sized properly.

Rich Waskowitz

We have run into more problems with IEC stuff than it seems to be worth in some cases. If you are going to take the IEC route, then you better understand the proper methods of short circuit and overcurrent protection to go along with them. For instance, You can put a 20 amp thermal mag trip breaker in front of a NEMA size 1 starter and run #12 AWG to a 1 HP motor and keep NFPA 70 and 79 happy. An IEC contactor might not be (probably will not be) listed for use with that type of breaker and now you have to go to a properly coordinated fuse or a more expensive current limiting breaker to keep the IEC things from blowing up if a short occurs downstream. IEC components are built pretty flimsily (for a reason) and do not have the energy withstand ratings that NEMA devices have.

The other problem we run into all the time when you start getting into that whole European / IEC mentality is 24 VDC control. There's a can of worms for sure. For instance, 24 VDC PLC input cards draw about 8 mA per input. You better make sure that every relay contact, limit switch, starter auxilliary contact, overload realy contact, etc. has contacts SUITABLE for reliably passing such a low current and voltage...........NOT ALL DO, especially when you start mixing NEMA componets in the same system.

Richard Neff

I did not see any specifics when people commented, so here are a few.

For many applications the IEC contactors will last virtually forever. In my main application, we start a pump twice a day and operate it for about 6 hours. Under that condition the IEC contactor will last "forever". When we have a jockey pump, we upsize the contactor to add life.

The NEMA starters provide no phase loss protection in 3 phase systems. A phase monitor is a must, but phase monitors are constant sources of problems and fail frequently. The IEC overloads have built in phase loss protection that is impeccable. Our company has built many thousands of pump stations with IEC overloads and we have to the best of our knowledge never lost a pump on "single phasing". The trip curve is dramatically shortened by a tilting trip bar when a phase is lost. When one of our customers doubts that we pull them into our shop and prove it. The last test we ran showed the motor overload tripping in about 3 seconds on phase loss.

The NEMA starters are difficult to install properly because of the multitude of heaters available, and no one will ever know if they work properly or if the heater was selected properly.

The IEC overloads appear by our experience to be very accurate.

The IEC equipment is more friendly to automation because the overload can be set to automatically reset itself, and then our PLC holds the pump off until someone presses the door mounted reset button. This simply cannot be done with a NEMA overload. With a NEMA overload the door would have to be opened and the overload reset button depressed, or a through the door pushbutton would have to be installed, and sometimes the heaters will not reset once tripped because the melting alloy disappeared.

For system designers the IEC system is easily configured, flexible, and often results in a superior system because it is more flexible, NEMA stuff has to be special ordered, the heaters have to be carefully selected and ordered.

In jogging situations (constant on/off actions) the contactors can be easily oversized. In light duty applications the IEC contactor is far more sensible than installing both a huge NEMA contactor with 1,000 years of life and a phase monitor installed that is another source of trouble.