Hand-Off-Auto

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electric1

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We are installing MCC's for a utility company. Their pumps are controlled from buckets in various MCCs. We have pointed out a potential problem (safety item)with their design. The HOA switches do not truly have a off position. If a limit switch, pressure switch, etc. is closed the pumps will run in the "auto" and/or "off" position. I believe this violates NEC 430-82. The utility says no and does not want to add the additional contact block at the HOA or just a "Hand / Auto" switch in the bucket door to correct the potential hazard.

There is an illusion of being able to turn the pump off at the HOA switch and even though this is not the disconnect (for maintenance) switch, there is the potential of someone turning the Hand-Off-Auto to "Off" and adjusting a shaft or something, believing the pump will not turn on.

Is this really not referenced in the NEC?
 
Re: Hand-Off-Auto

disconnect requirements are in section 430.102. You are referring to the control circuit which is not the type of disconnect required in 430.102
Its a bad design. Off should be off. However one should never rely on a HOA switch to deenergize the driven load.
How do you turn off the pumps? with the disconnect?
 
Re: Hand-Off-Auto

The HOA is not the controller. See the Definition in 430.81.

As long as the motor and controller disconnecting means are installed properly per 430.102 what you have described so far may be poor design, but "legal."
 
Re: Hand-Off-Auto

The HOA is not the controller. See the Definition in 430.81.
Click to expand...
Neither is a start or stop switch. I have just recently realized that a controller has the motor current flowing through it (motor circuits have never been my strong point). Before, I thought a motor controller was a place where you could start or stop a motor.


Steve
 
Re: Hand-Off-Auto

Electric1, The "H.O.A" ,what is the contact blocks configuration? It should be 2 N.O. contacts, it sounds to me like you have a N.O./N.C. type. This situation doesn't sit well with me either.
 
Re: Hand-Off-Auto

Electric 1,

The HOA selector should be wired so that all control circuit current flows through it before going to any of the manual (push-buttons) or automatic (pressure sw, limit sw. etc) pilot devices.

Ed

MotCon10.gif
 
Re: Hand-Off-Auto

This sounds like a lift station for sewage. And the HOA is only there to test the pumps. In this case to by-pass the float limits to run the pumps for testing and should not even have an off position? So if you can get permission just use a marker and block out the off word or symbol, I did four of these and had the same thought and the service tech got the permission to just block out the word off as it didn't do anything in that position anyway.
 
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