Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Need Guidance regarding E-stop implementation per NEC and UL508C

Need Guidance regarding E-stop implementation per NEC and UL508C

Need Guidance regarding E-stop implementation per NEC and UL508C

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

RE: Need Guidance regarding E-stop implementation per NEC and UL508C

  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

RE: Need Guidance regarding E-stop implementation per NEC and UL508C

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
or details (NFPA 79-1997)

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close