Contactor derating

Has anyone out there seen or know where there is a derate table for parralled legs of a contactor. To explain better if a contactor is rated 100 amps for a 3 phase load what would be the derate factor if you parralleled single phase through all three legs. I know it would not be 300 amps (probably because 1 leg would close slightly before the others and for this msec carry all the current) but I seem to remember seeing a derate table for this scenario. I have searched the web but cannot find anything. Regards Alan Case

Wouldn't that be part specific?

For example, the AB 700PK relay has 20A contacts. They sell a kit to tandem two contacts for 35A. There is no chart just a rating on the kit.

When using Telemecanique contactors in AC-1 applications (power factor =>.95) the factors are:
2 poles in parallel: k=1.6
3 poles in parallel: k=2.25
4 poles in parallel: k=2.8

They make no mention of using parallel contacts to control AC motor loads, however they do make mention of increased contact life but not increased operating current for DC loads. (source catalog #8502CT9901R2/01 available at http://www.squared.com

The contactor closure time wont delay any more then the ramp time to obtain full current. Technically if it states 100A a leg then it can do that BUT there is always a power factor involved, all things being equal then current flowing in parallel paths should be equal.

I havent found my IEC complete listing for contactors but I found the NEMA stuff which is actually more conservative than IEC.

You can goto http://www.nema.org and do a search thru their standards (you have to register to download). OR you can get it from my website
Industrial Control and Systems: Controllers, Contactors, and Overload Relays, Rated Not More Than 2000 Volts AC or 750 Volts DC
http://mywebpages.comcast.net/rsdoran/ICS2.pdf

Hopefully this will help

Wow almost missed this one NEMA and IEC Devices for Motor Service — A Guide for Understanding the Differences

Thanks Ron. I will check it out. Alan