Need Guidance regarding E-stop implementation per NEC and UL508C

[larryg]

Hello all,

I am in the midst of a redesign and am coming up against some problems with management regarding E-stop (emergency stop) implementation in a motor drive amplifier. Could someone who has experience with this particular facet of the NEC or UL comment? I originally asked this question before in terms of a PCB mount contactor. However, it is clear that there are facets of the code that I don't yet understand. Here are the details:

We manufacture both a controller and amplifier designed to drive three-phase brushless motors. Our amplifier runs off of 120VAC (3 ph) and provides a bus voltage of 140DC at 20 A cont. (40A pk).

Our existing E-stop circuitry involves connecting the E-stop button to a AC Contactor that supplies the drive power (120VAC) to the amplifier. If the button is pushed, the contactor opens, the drive power is removed and the motors will coast to a stop (I believe this is a Category 0 stop).

There is a push to integrate this E-stop circuitry into the amplifier itself, thus making it Plug-n-play, so to speak. However, the physical size of a force-guided contactor (which I believe is required for this application)designed to carry the 40A makes it impossible to integrate into the unit.

So, the big question is, are there alternative methods available that would meet the safety standard, but would allow for smaller components or implentation at a different point? Management is not willing to give up the idea unless I can provide some sort of documentation that specifically states it must be done externally and in a specific way.

I apologize for being so long winded, but I felt it was necessary to provide as much information as possible.

Thanks for any assistance. BTW, I have posted this message in the standards forums (NFPA and UL), but it appears they don't get much attention.

Larry G

 

[don01]

larry,
I haven't responded to date since I live under a different set of standards. I can tell you if you want to comply with AUS/NZ standards you would need the forced contacts.
As a matter of course we wouldn't use your estop cct we would mount certified contactors external to the control unit. and put the neccessary control cct into the controller.
Is the input current less than the peak output? IF the peak is supplied by caps etc and the discharge time is quick, would you meet the standard with a smaller input contactor. Or how about upping the input voltage. Sorry I aint got a lot to offer keep us informed, If I get any more dumb ideas I will post them.

regards Don

 

[jbartos]

Suggestion: Contact the E-Stop and associated control equipment manufacturer, e.g. Allen-Bradley, who may have literature available for the E-stop applications and interpretation in USA and Europe. There are standard and norms that cover the E-stop application. Essentially, the E-stop is supposed to be an easily accessible stop switch (sometimes within prescribed maximum distance but within the machine operator reach). There are additional standards convering this in USA, namely NFPA. Check

http://www.nfpa.org

http://www.nfpacatalog.org/cgi-bin/SoftCart.exe/STORE/PAGES/79-97.htm?L+nfpanonmembers+nqmn1484

or details (NFPA 79-1997)