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 UL 508/508 comment?  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 but  ton 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 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

Larry G

Larry: Couple of question.
What is the HP and full load current of the motor?
Is this unit UL Listed?
Is the Overload external or internal?

Hi Reddog,

The amplifier is capable of supplying 7 kVA total, 3.5 kVA/axis  (40 A pk, 20 A cont.)  Motors will be varied, depending on the application.

This particular amplifier is not currently UL listed.  One of the facets of this redesign is to get it UL listed.

As for overload, the amplifier has a built-in over current trip point which will generate a fault signal and disable the drive.

My thoughts are that since the contactor is not directly connected to the motor (as it appears is the case in many applications)but connected to the amplifier that drives the motor, we might be able to get away with some lesser safegaurds.  But then again, I probably don't know what I'm talking about as I am new to this industry.

Thanks,
LarryG