hand off auto - wiring a mcc bucket


Thread Starter


I'm being asked to wire a mcc bucket, that controls a vent hood, so that the HAO in hand: power will come off the hand set of contacts, then go through a remote located switch, then to the motor starter. I think that this should happen only in auto, and that hand means hand only. Am I wrong?

Related: Are vent hoods required to be tied into the fire protection system?
OFF - control circuit de-energized

AUTO - the rungs containing the automatic controls are energized unless in the OFF or HAND position

HAND - enables the rungs for local manual control.

OFF is not a disconnect of power from the motor, as it only applies to the control circuit.

AUTO - is self explanitory as the motor switches on or off according to some logic such as sensors or relay contacts controlled by another system.

HAND - Can have several meanings depending on it being local to the motor, or being remotely located. It can also be "momentary" with spring return to OFF, basically serving as a "START" contact that is sealed in by the motor RUN contact.

A lot of this depends on the companies own practices and the type of industry.

I believe it is common safety practice to shut off all ventilation fans/blowers in the case of fire. This minimizes the risk of causing the fire to spread especially in occupied areas. At the same time this has to be coordinated with any automatic fire protection systems.