Need guidance re: E-stop implementation for motor drive circuit

[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 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 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 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

 

[jw62]

Larryg,
According to NFPA 79, Electrical Standards for Industrial Machinery, the E-stop on a machine can be a category zero or one. A category zero immediately removes power to the "machine actuators", whereas a category zero brings the machine to a controlled stop and then removes the actuator power. My best efforts to nail this down, coupled with the design of machines I see lately, yields the interpretation that "machine actuators" are contactors, push-buttons, etc., that is, control power. I don't see many machine builders actually taking away the main power (3 phase 120v in your case). It is stated, if the E-stop is a category one, that the final action of removal of power to the machine actuators can only involve electro-mechanical components. Then again, if your drives are UL listed or tested by a laboratory, I would think they would have to take the buck on this. Anyhow, I hope this helped.

 

[larryg]

jw62,

Thanks for the reply. Unfortunately, that project has been put on hold for awhile. However, it may rear its ugly head later this year.

Your reply gave me alittle bit more to consider. Thanks.

LarryG