Shock from motor terminal of PF40

SJT

New member
Location
OH
Hi all, new here but want to share and learn.

Today I was troubleshooting a bottle spacing conveyor that was powered by a powerflex4 drive. I'll start by saying the motors were not wired correctly. I say Motor(s) because 2 motors are being driven with a single drive. The drive is wired to two separate overload devices which then feeds the two motors. While troubleshooting why the motors were not running.....
1. I found the voltage coming out of each overload device to match the Hz on the drive.(480 VAC or so).
2. The 2 motors had quick disconnect plugs AFTER the overload going out to the motors.
3. I had disconnected and taken one apart when I checked continuity between the 3 motor phases(this was how I determined the motor was wired incorrectly).
4. I pulled the cover off the j-box for THE OTHER MOTOR(unknowingly) and started touching things. Shame on me.
5. So I ended up getting whacked by what I assume was 277(one phase terminal) and it hurt allright but I'm wondering if this type of shock depends on how well you are grounded ??? It didn't feel THAT much worse than 120VAC. I think the drive was set just about 60 hz at the time. I'm pretty sure my other arm was on top of the motor, current went through shoulders? Top of chest?

I'm curious to hear some input but if your response starts with "You dumb SOB...." please don't respond.

Thanks
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
So... you did NOT kill line power to the VFD while working on the circuit?

If so, there’s your sign... A VFD is not a disconnecting device, that’s why it needs to have one ahead of it, and that’s why LO/TO rules exist.

ALL power electronic devices have “leakage current” through the components themselves or the protection devices for the main components. VFDs in particular (as well as UPS and servo drives) have DC bus capacitors that store energy for a relatively long time even after the line power is disconnected. Most will come with some form of indicator that tells you when there is still energy on the DC bus, sometimes it is whether the display is still active, but other designs kill the display immediately so you must look for an LED or something. All of that will be outlined in the “warnings” section at the beginning of the manual for you VFD.

And just so you know, there is nothing wrong with running two or more motors on the output of a VFD, so long as you have an OL relay for each motor.
 
Top