MCP with OL protection in a VFD located in a separate downstream enclosure.

corvalan

corvalan

Member
Is it a violation of the NEC or UL (for the MCP), the following installation:

1. An MCC bucket has only an MCP.
2. Downstream from the MCC, there is another enclosure with a VFD that includes an OL protection function.

I understand that the NEC motor protection requirements are satisfied by this arrangement. However, I am concerned about installing an MCP in an MCC bucket without OL protection in the same bucket. Is this a violation of the NEC, UL 508 (if it applies) or UL 845 (if it applies)?
 
So there is a circuit breaker at the MCC and it is feeding a VFD which is feeding the motor? That is a standard installation practice. The OCPD at the bucket is sized according to the recommended OCPD value for the VFD and the conductors to the VFD are sized at 125% of the VFD input current value.
 
You can only use an MCP (assuming you mean instantaneous only breaker) as part of a listed combination starter. The proposed installation would not be permitted.
 
Had an argument with an electrician in a hospital where we were changing out a cooling tower. The tower motor was fed from a VFD that had been added after the original install. The original install fed from the MCC bucket had a MCP and motor starter . That was legal adding the drive and bypassing the starter was the violation. We were just supposed to change the tower. Everyone was riding my A-- telling me I was wrong but I knew I wasn't.

I finally convinced them to take the MCP out and put a breaker in
 
Eddie702 said:
Had an argument with an electrician in a hospital where we were changing out a cooling tower. The tower motor was fed from a VFD that had been added after the original install. The original install fed from the MCC bucket had a MCP and motor starter . That was legal adding the drive and bypassing the starter was the violation. We were just supposed to change the tower. Everyone was riding my A-- telling me I was wrong but I knew I wasn't.

I finally convinced them to take the MCP out and put a breaker in
Click to expand...
I retired from a large hospital that was built in the 1970's and over a hundred starters inside of MCC 's with either breakers or fuses that were changed over to VFD'S. We always ordered drives with a disconnect and factory installed input fuses. For some reason the ABB there pole factory installed disconnect switches up to 75 HP were not the best quality both in ABB & Danfoss drives. We never turned them off with drive running. The three pole factory installed 100 to 250 HP disconnect switches were great. Never had to replace any of them. Kept thin wax string in my PM cart to pull up thin square maybe 8 to 10" long rod that went from back of drive cabinet to door mounted disconnection operating lever.
 
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