Selecting a contactor for power control 2

[dxjenkins]

I am trying to select a contactor that will feed 3 circuit breakers. The CB's feed three servo motor drives. Two 20A CB's and one 15ACB. The CB feeding the contactor is 60A.

Since this contactor is being used in a power on/off application for the drives and not directly to the motors, what Contactor rating is critical AC1 or AC3? Can I size the contactor at the potential max load or do I need to consider max scc of feed?

Thanx
Dxjenkins

 

[PaulBr]

Forgive my ingnorance. What is AC1 rating and AC3 rating of contactors.
Thanks
PaulBr

 

[dxjenkins]

AC1 & AC3 are ratings refer to the type of load.
An AC1 rating of X amps states that the contactor is rated for X amps with an Inductive load. Or "Slightly Inductive load" as they state it. AC3 rating I think is for non- jogging motor applications. There are other categories as well.

I am not sure of all the specifics oo whcih situation they apply to, which is the main reason I posted the question.

Sorry not much help but enough to get you started like me!

 

[fangas]

AC1, is for an AC load that is essentially resistive,
PF >.95
AC3, is a typical motor contactor designed to handle inrush when closing & FLA when opening.

My rule of thumb with IEC contactors is to look at the AC3 curves and go up 1 frame size.

However, if your purpose with this contactor is as a Master Contactor, simply to supply power to the drives and act as disconnect, after the motors have been stopped by the drives. *Not* to control the motors themselves (leaving that to the drives), I'd say you would be safe choosing an AC1.

*If* your drives are going to remain enabled and you're going to use this contactor to operate the motors via supplying power to the drives. I suggest you don't. Your drives won't like it. I also suggest that you don't use it to cycle power to the drives either, whether the motors are running or not. They won't like that either.

Refer to your drive manuals and/or the Mfg's for some advice on this type of application.

Hope that helps

Ed