I'm redesigning the control system for a 2 hp 208VAC 3 ph motor that uses a VFD for braking. The only load on the motor during braking is a saw blade. The VFD (Yaskawa V-1000) has inputs for "Run" and "Stop" through N.O. and N.C. momentary switches, respectively. I have verified that if there is a loss of line power while the motor is running that it (the motor) will not automatically restart upon restoration of power - the "Run" switch must be pressed. This behavior is the same as that of a simple control using a magnetic contactor (MC) or motor starter w/o a VFD. Upstream of the VFD will be a molded case circuit breaker (MCCB) with an enclosure door interlock.
The Yaskawa manual states on one page, "Use an MC to ensure that line power to the drive can be completely shut off when necessary. The MC should be wired so that it opens when the drive fault output is triggered." In another section it states, "The drive should be shut off in the case of a fault in external equipment such as braking resistors through use of an MC." and "NOTICE: Install an MC on the input side of the drive when the drive should not automatically restart after power loss. . . . Use the drive to stop and start the motor."
I can completely shut off power to the VFD with the MCCB. I'm OK with the drive restarting after a power loss, because the motor won't restart automatically. The drive is used to stop and start the motor. I don't have any external equipment such as braking resistors. So, is there any reason I need an MC between the MCCB and the VFD? And, if I put one there and wire it so that it opens when the drive fault output is triggered, how would I reset the fault with the VFD powered down?
I've attached a diagram as it stands without an MC. The SMS is a back-EMF stop motion sensor for the safety interlock.
The Yaskawa manual states on one page, "Use an MC to ensure that line power to the drive can be completely shut off when necessary. The MC should be wired so that it opens when the drive fault output is triggered." In another section it states, "The drive should be shut off in the case of a fault in external equipment such as braking resistors through use of an MC." and "NOTICE: Install an MC on the input side of the drive when the drive should not automatically restart after power loss. . . . Use the drive to stop and start the motor."
I can completely shut off power to the VFD with the MCCB. I'm OK with the drive restarting after a power loss, because the motor won't restart automatically. The drive is used to stop and start the motor. I don't have any external equipment such as braking resistors. So, is there any reason I need an MC between the MCCB and the VFD? And, if I put one there and wire it so that it opens when the drive fault output is triggered, how would I reset the fault with the VFD powered down?
I've attached a diagram as it stands without an MC. The SMS is a back-EMF stop motion sensor for the safety interlock.
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