JAbrahams5
Member
- Location
- Colorado
- Occupation
- Master Electrician / Project Engineer
I am in a situation where the local Fire Department is requiring the VFD's controlling some HVAC equipment (MAUs) to be moved into 2 hour rated rooms for survivability as these provide a function for smoke control. The drives are currently integral to this equipment, downstream of the single point of connection. Feeder raceways and conductors have already been installed to these units. I can think of 2 ways to rework the power configuration on these, but both leave me wondering if the installation will be code compliant.
Option #1 is to intercept the feeder conductors after the single point of connection, run them to the new VFD location and back, terminating on the existing contactor that is controlled by BAS. The caveat to this is that I need to provide auxiliary contacts to monitor the disconnect position via the Fire Alarm. The current disconnecting switch on the unit will not except auxiliary contacts. I can remove this, install a new disconnect with aux contacts, but this would in turn shut off the entire system including the VFD. Alternately, I could keep the existing disconnect on the line side, and put the new disconnect just upstream of the motor load. Is it legal to have 2 disconnecting means on one piece of equipment?
Option #2 is to intercept the existing feeder raceway, reconfigure the drive in series, and separate out the controls in the unit as they cannot be subject to the VFD frequency changes. This would have to be single phase 480, requiring power monitoring by the Fire alarm system. It would require local disconnecting means, which in turn puts me in a situation with 2 disconnecting means serving the unit. I welcome any input and appreciate all comments on a complicated situation.
Option #1 is to intercept the feeder conductors after the single point of connection, run them to the new VFD location and back, terminating on the existing contactor that is controlled by BAS. The caveat to this is that I need to provide auxiliary contacts to monitor the disconnect position via the Fire Alarm. The current disconnecting switch on the unit will not except auxiliary contacts. I can remove this, install a new disconnect with aux contacts, but this would in turn shut off the entire system including the VFD. Alternately, I could keep the existing disconnect on the line side, and put the new disconnect just upstream of the motor load. Is it legal to have 2 disconnecting means on one piece of equipment?
Option #2 is to intercept the existing feeder raceway, reconfigure the drive in series, and separate out the controls in the unit as they cannot be subject to the VFD frequency changes. This would have to be single phase 480, requiring power monitoring by the Fire alarm system. It would require local disconnecting means, which in turn puts me in a situation with 2 disconnecting means serving the unit. I welcome any input and appreciate all comments on a complicated situation.