Fan Shutdown Relays

[Benihana]

When a HVAC unit has supply and return fans with their own VFDs, is a fan shutdown relay needed for each fan? Or is one relay capable of shutting down all fans.

 

[infinity]

I would think that a relay is required for each fan because the relay will open the control circuit each individual VFD. I would guess that you could use a multipole relay to ensure that each control circuit is isolated. I would like to hear some other opinions.

 

[Benihana]

I would think that a relay is required for each fan because the relay will open the control circuit each individual VFD. I would guess that you could use a multipole relay to ensure that each control circuit is isolated. I would like to hear some other opinions.

I would have imagined the same...that one would be needed for each VFD.

 

[garbo]

We had a lot of AHU units that all the ones above 60 HP would have two supply fans & one return fans. Johnson Control ( JCI ) or Siemens BSO took care of the speeds and start stopping of them. For some reason in two buildings you could not start return fan unless at least one supply fan was running. For at least the last 30 years drives that I worked on had at least one internal relay that you could program. Did not like to use these little 3 or 5 amp rated relays to control any loads pulling more then halve a amp. Lot cheaper & faster using an ice cube relay for controls. Some drives you might have to spend over ten minutes to remove the control board with these miniature relays mounted on.