Absolute Noob Emergency Stop Controller Question

[Eng8492]

I am using an emergency stop controller. When the emergency stop control is triggered, the output from the control should open a 2 pole contactor carrying split-phase 240VAC and a 3 pole contactor carrying 3ph power. Because I cannot find an e-stop control with any pilot duty ratings (ie UL508 Axx, Bxx, Cxx) which guarantees it can drive the contactors directly, I was planning on using pilot duty relays in between the controller and the contactors. Is there any problem with this approach?--safety requirements are minimal-- ie IEC Sil Level 0). Basically the customer just wants a visible E-stop function.

 

[davidbeach]

Why not just use breakers with an Under Voltage Release and run a voltage circuit through normally closed contacts of the E-stop? When the E-stop is pressed, the voltage is interrupted and the breakers open.

 

[Eng8492]

I think that is an alternate solution if the voltage through the Estop buttons is within the rating of the switch AND is non-hazardous. But now, instead of picking out an Estop controller, I have to check out those two factors and search for undervoltage breaker. Then paint the breaker handle green and make it externally accessible with a restart label...too much for my application. Great idea though.

Since I have posted this, I have done much research and learned that this approach is acceptable for some categories of protection. The universal recommendation is that any relay or contactor used to augment the voltage/current/isolation rating of the safety controller's contacts is performed with force-guided contactors or force-guided relays.

Force-guided relays/contactors cannot have any poles in a mismatched state. I am not sure what the purpose of this requirement is, if someone could treat this as my second question.

 

[LionelHutz]

How big are these contactors and what are the coil requirements? The E-stop buttons I use have heavy duty contacts capable of directly operating the coils of most typical contactors in use.

 

[Eng8492]

Thanks for your interest Lionel. The total load is 3A to guarantee pull in. Im looking for a din rail transorb to prevent arcing.
But I am going to use the controller because it implements e-switch contact monitoring, voltage monitoring, and manual restart with a minimum of wiring.

 

[norcalnewb]

My personal preference is to make e-stop circuits as simple as possible. I want to know they are going to work when needed. Your original approach will work, but look at the number of devices you are adding to this system with a controller and additional interposing relays. On the larger motors I work with with electronic motor protection relays, I let the relay handle almost all starts and stops, such that everything is an input into the relay and all logic is done inside the relay. The one function I don't wire through the relay is the e-stop. I wire a contact off the e-stop into the relay to record this action, but I don't want a problem occuring that prevents a motor shutdown and use hardwire contacts off the button in the coil string to guarantee shutdown. I would agree with Lionel that the good, old simple mushroom head button is a good solution to e-stop.