pushbutton station disconnect?

[mjmike]

This souns like a basic question until reading into it. When dealing with a remote motor from the MCC, there is typically run/stop pushbutton station at the motor and the contactor is in the MCC. At the motor there will obviously be the motor local disconnect, but there should also be a disconnect for the pushbutton station because by definiton, the pushbutton is a controller. Anybody have experience with this as how to only have 1 disconnect at the motor?

Or, does it make more sense to have the MCC only provide the power and put a combo starter disconnect at the motor? The MCC usually has a hand/off/auto switch as well which is why the contactor is usually in the MCC. I believe hand lets the pushbutton station work, off is obviously off, and auto is alwas on I think. There are also red and green LED for motor run and motor stop.

Thanks

 

[don_resqcapt19]

A push button that operates a stater is not a controller.

 

[eric9822]

Mike,

Check the definition of "Controller" in Article 100. The contactor is the controller, not the pushbutton. There is no requirement for a disconnect of the control circuit at the motor. We rarely install local disconnects at motors unless they are specifically required because we are an industrial facility and follow the exemptions to 430.102 (B)(1). In cases where we want or need a local disconnect we install a set of auxilliary contacts in the disconnect that opens the control circuit along with the power circuit.

 

[mjmike]

I have read the definition of a controller multiple times. I may need to re-read as it would like the push uttons are a controller. I like the idea of auxiliary contacts in the disconnect though.

 

[don_resqcapt19]

The rule in question requires a disconnect for a motor controller. The push button is not the motor controller. I guess you could say it is the controller for the motor controller, but there is no disconnect rule for that "controller". While 430.102 does not use the term "motor controller", it is clear from the wording of the section, especially the wording in 102(B)(2), that the controller that requires disconnection is the motor controller.

 

[eric9822]

I have read the definition of a controller multiple times. I may need to re-read as it would like the push uttons are a controller. I like the idea of auxiliary contacts in the disconnect though.

Mike,

Controller. A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected.

The contactor is what delivers power to the motor, not the start pushbutton. Like Don says I guess you could consider the pushbutton the controller for the contactor but I have never heard it referered to that way.

From the NEC 2008 Handbook:

A controller may be a remote-controlled magnetic contactor, switch, circuit breaker, or device that is normally used to start and stop motors and other apparatus and, in the case of motors, is required to be capable of interrupting the stalled rotor current of the motor. Stop-and-start stations and similar control circuit components that do not open the power conductors to the motor are not considered controllers.

 

[steve66]

Or, does it make more sense to have the MCC only provide the power and put a combo starter disconnect at the motor?
Thanks

Usually, the whole point of having an MCC is to have the starters (and associated controls) at one location. so if you move the starter to the motor location, there doesn't seem to be much point in having an MCC.

I agree with the other, the pushbutton is not a controller. However, you need to read 430.102(B) to make sure you don't need another disconnect at the motor.

 

[kwired]

I have read the definition of a controller multiple times. I may need to re-read as it would like the push uttons are a controller. I like the idea of auxiliary contacts in the disconnect though.

The push button is no more of a controller than a selector switch, limit switch, pressure switch, thermostat, etc. These are all accessories that drive the controller which directly operates the motor. For smaller motors (usually 1HP or less and single phase) sometimes these types of devices are the controllers, but only if they directly switch current to the motor.

 

[don_resqcapt19]

The push button is no more of a controller than a selector switch, limit switch, pressure switch, thermostat, etc. ...

I think that these are all controllers, but they are not motor controllers and the code rule requires a disconnect for the motor controller. However the code rule does not specifically say that. The rule in 430.102 should use the term "motor controller" in place of "controller".

 

[kwired]

I think that these are all controllers, but they are not motor controllers and the code rule requires a disconnect for the motor controller. However the code rule does not specifically say that. The rule in 430.102 should use the term "motor controller" in place of "controller".

You are probably right with that. Adding that one word would clarify it quite a bit.