Hey all, new conveyor panel coming in for our infeed line. PowerFlex 525, 5 HP, a 440R dual channel relay for the two E-stops. Our old panels all have a 100S contactor the relay drops.
The panel builder wants to drop the contactor and take the relay outputs straight to the drive's S1 and S2 terminals. Saves panel space and a part, and he says the drive's STO "is rated for it". I asked for the certificate and got a brochure.
I've read the safety section of the 525 manual twice, and on the bench unit with a 5 s decel set the drive just coasts on STO. Our safety guy is out for three weeks.
Half of me says STO is enough these days, the other half says keep the contactor. Which is it? The conveyor is flat, no incline, no brake. Not sure what I should be asking the panel builder for either, because a brochure isn't going to do it.
Which stop category does the risk assessment require for that E-stop? STO is stop category 0, the drive removes torque and the motor coasts. If a controlled stop is required before the torque is removed, that is SS1, a different function. On a SINAMICS it is the same, the drive family does not change the question.
RA from the old line says category 0 for the E-stops, and this is the same layout. Flat belt, light load, it coasts to a stop in a couple of seconds on the bench with a box on it. So category 0 is fine.
Then STO is a valid stop function here. Your panel builder is right for this panel and wrong to say always. Three things before you drop the contactor.
Both channels. S1 and S2 each from their own relay output, not one output jumpered to both. The PF525's STO is rated for a PL only when used two channel, the figure is in the manual's safety section, not from me.
The contactor's other job. For E-stop, STO replaces it. If anyone used it as isolation for cleaning the belt, STO is not isolation, keep the disconnect and the lockout.
Monitoring. I don't remember the 525 giving you a contact to prove STO opened, for the relay's feedback loop. Check the manual. If not, that's for the safety guy's list.
So the decel time does nothing at all once STO opens, I guess? We set 5 s on every conveyor and I always assumed the E-stop used it.
Nothing. The drive isn't stopping the motor, it's refusing to make torque. Decel ramp or not, the belt coasts. That's what category 0 means.
Went with STO on the 5 hp PF525. Both relay outputs to S1 and S2 on their own wires, contactor dropped, disconnect on the door stays for lockout. Safety guy came back early, went through the manual's safety section with us, signed it for this PL, said the feedback loop question is fine for what this line needs and didn't explain why. Tested with a box on the belt, coasts about two seconds.
The argument came down to a question nobody had asked, which stop category the RA wants for that E-stop. It wants category 0, and category 0 is exactly what STO gives you.
I still want to know what he saw about the feedback. Thanks danr40 and gunther.
STO for the stop, the disconnect for the lockout. Two different things.