IEC vs NEMA Contactors

[cfuller]

I'm writing a bunch of specifications for new equipment especially new bridge cranes. I've been told two different stories regarding using NEMA contactors vs IEC contactors. I've been told that NEMA contactors are superior and heavier duty but then have been told NEMA contactors are costly and not that big of an improvement over IEC contactors if the system is on a VFD. Any thoughts or experiences would be appreciated.

Thanks

 

[itsmoked]

That's pretty much true. NEMA are beasts. They also cost 3 to 4 times what IEC ones cost. They are considerably more massive being about twice the size with equal ratings and so can take screw ups and abuse much better.

They're so expensive that they are generally considered to be repairable. If one chokes you take it apart and find the damaged bits and replace them.

That's the theory anyway. I've found that to be hog-wash because finding the exactly right obscure bits and having them sent to you is a crap-shoot that can get frustrating and expensive.

If you were running a hoist via plugging, and jogging then NEMA contactors would probably be the go-to ticket. If instead the hoist is mostly controlled by a VFD then I'd not waste the space and dollars on NEMA and would grab for IEC like a person in the ocean grabs for a lifeboat.

That said I tend to always go a size bigger in the IEC than recommended. It will still be a fraction of the NEMA price.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Keith.
Some history of 'repairable' NEMA contactors.
I started in the days of all NEMA contactors and "U" frame motors.
Jogging and plugging were common.
I had one machine, an industrial lumber planer, that would occasionally jam.
If the jam wasn't cleared withing seconds the board could explode, and the machine would have to be opened to clear the wood fiber.
There was a normal start button but no stop button. The machine was stopped with a jog reverse button.
(One time the welds holding the stator to the motor housing failed and the stator spun inside the housing. I repaired the cut off leads and the millwrights welded the stator back in place and it was business as usual.)
We stocked replacement contact sets and replacing contacts was a normal task on contactors under heavy use/abuse.
Then came the "T" frame motors.
With "T" frame motors it is not possible to abuse a contactor as could be done with a "U" frame motors.
If "T" frame motors were subject to some of the abuses that were common with "U" frame motors in sawmills, you would be replacing motors weekly instead of contact sets anually.

That said I tend to always go a size bigger in the IEC than recommended.

I agree with that solution with the present class of motors. ("T" frame)

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!