VFD Safety Circuit

Christoff84 · Jun 12, 2018

Vager said:
Unfortunately I do not have the STO option on these drives so it looks like I'm stuck with the contactor and programmable safety relay strategy. Currently the circuit already has a disconnect with early break contacts which operate the coil of another contactor. Both of these are located between the VFD and the motor. As of now since I have to drop power to multiple VFDs at once I plan on using a safety contactor in series with several of the early break contacts to disable the drive circuits and at the same time de-energizing the contactors located between the disconnects and the VFDs. If I'm interpreting this thread correctly that configuration should stop the motors and not damage the VFDs.

Just out of curiosity, what size is this VFD? It might be cost effective to replace it with a unit that has STO. The powerflex 525's aren't overly expensive and come with STO.

jraef · Jun 12, 2018

On all of the disconnect switches I have seen, the aux contacts are actually always designed to open ahead of the main contacts and close after them. Some mfrs go out of their way to explain that, some don't bother, but even on the ones that don't bother to tell you (without digging deep) are still designed that way. I only recently found out about that, for years I was investigating it every time, then someone told me that it is part of NEMA KS-1, UL98 and UL508.

VFD Safety Circuit

Christoff84

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jraef

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