Creeker
Member
- Location
- Hickory, NC
In a 480 VAC 3 phase, 30 ton roof top chiller unit with 1 compressor motor and several other smaller fan motors, the power to the unit comes from a breaker in a panelboard and is routed up to the unit. The conductors from the panel board are landed onto lugs inside of the unit that have multi tap connections. The power from the taps goes to several smaller motor starters and to the compressor contactor. The smaller 3 phase motors each have their own contactors with fuses and thermal overloads.
One set of conductors goes from power tap to the compressor's contactor. The size of the conductors to the compressor's contactor is smaller than the main feed from the panelboard. The compressor's contactor does not have thermal overloads or short circuit protection (e.g., no fuses or breaker). Article 440.52(A) (NEC 2011) may allow for the lack of thermals if integral thermal protection is provided. However, does the compressor motor require its own short circuit protection (e.g., fuses/breaker)? How does Article 430.51 figure into the configuration?
As it is configured now, the short circuit protection for the compressor motor is provided by the breaker (it may be HACR rated) in the panelboard located on the main level. Does the compressor motor require its own short circuit protection (e.g., fuses/breaker) like the smaller motors?
Note, this is an old unit. The exact history of this unit is not known.
One set of conductors goes from power tap to the compressor's contactor. The size of the conductors to the compressor's contactor is smaller than the main feed from the panelboard. The compressor's contactor does not have thermal overloads or short circuit protection (e.g., no fuses or breaker). Article 440.52(A) (NEC 2011) may allow for the lack of thermals if integral thermal protection is provided. However, does the compressor motor require its own short circuit protection (e.g., fuses/breaker)? How does Article 430.51 figure into the configuration?
As it is configured now, the short circuit protection for the compressor motor is provided by the breaker (it may be HACR rated) in the panelboard located on the main level. Does the compressor motor require its own short circuit protection (e.g., fuses/breaker) like the smaller motors?
Note, this is an old unit. The exact history of this unit is not known.