Category 3 Safety Circuit with a VFD
Category 3 Safety Circuit with a VFD
(OP)
I have a light curtain project and I'm using a Rockwell CR30 Programable Safety Relay. I will have the double contact safety switches and all. I know I need to have 2 safety contactors before the motor. My question is the motors are driven by PowerFlex 40 drives with the Safe Off feature. Do I still need to have the double safety contactors between the drive and motors or will one contactor be sufficient, or have the contactor(s) on the line side? Thanks in advance.
RE: Category 3 Safety Circuit with a VFD
Keith Cress
kcress - http://www.flaminsystems.com
RE: Category 3 Safety Circuit with a VFD
So ... Probably ... Dual channel safety relay output directly to dual channel drive STO inputs, 3-phase power to drive with no external contactors, 3-phase drive to motor with no external contactors ... unless the instructions for your particular drive recommends otherwise.
Of course, all of this discussion is under the presumption that the hazard that you are mitigating is "powered motion". You still of course need a lockable disconnect switch, circuit breakers or fuses, etc for lock-out and circuit-protection and so forth - but not additional motor-starter contactors.
If risk asseessment requires PL e then the drive's PL d certification isn't good enough - but that's often in a "hazard elimination or hazard substitution" situation to reduce the risk by some other means.
edit just to ensure awareness: Structure categories, performance levels (PL), and risk evaluation is as per ISO 13849-1.
RE: Category 3 Safety Circuit with a VFD
RE: Category 3 Safety Circuit with a VFD
But if you are going to change drives, just change to the PF525, it has the STO built-in and is qualified to be able to attain Cat 3 PLd without needing to add the contactors.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Category 3 Safety Circuit with a VFD