Split distribution and 2 disconnects for cleaning?

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metalformer

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Hello Mike
Hello Forum,

I have seen it done where a portion the total machine is disconnected by a sub-safety disconnect. Meaning the main disco above drop out everthing and the lower sub-disco drops out all but maybe a dust collector to be used while cleaning the machine. Questions:

  1. Is this legal?
  2. Is splitting the distribution this way the best way, or do you have better suggestions?
  3. Is it over kill and this can be done with machine still fully powered, but the unwanted operation machinery disabled via control ie. keyed selector switch that is locked in a lock box during cleaning and all apply their locks to the lock box?
 
When it concerns motors, you really need to take a look at NEC 430.102 as there are some exceptions which might be applicable but, in general terms, a motor must have a disconnecting means that opens the actual ungrounded supply conductors to the motor. Opening a selector switch that simply interrupts the control circuit will not suffice as the required motor disconnect.
I know of no Code requirement that prevents you from addressing portions of machinery as long as you comply with applicable Code for that portion such as 430.102(A) & (B) and 430.75
 
augie47 said:
When it concerns motors, you really need to take a look at NEC 430.102 as there are some exceptions which might be applicable but, in general terms, a motor must have a disconnecting means that opens the actual ungrounded supply conductors to the motor. Opening a selector switch that simply interrupts the control circuit will not suffice as the required motor disconnect.
I know of no Code requirement that prevents you from addressing portions of machinery as long as you comply with applicable Code for that portion such as 430.102(A) & (B) and 430.75
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That is my take on the situation. The motor starters may be dropped out and also may not close with the selector switch in the cleaning position, but the supply voltage is still present at the top of the contactors. One thing to note; this is a central control or MCC so all the starters are in one cabinet with one disconnecting means, the main. I am on the right track then. This was just a situation I disagree with, but heard the age old "this is how we've always done it". Lucky for them I am in a position to change that. I plan to continue with the dual disconnecting means. As long as one or the other disconnects is open the dangerous motor will be offline. If the wrong disco is dropped out the dust collection won't run either.
 
The NEC does not cover machine safety switching. I'd look at NFPA 79 and NRTL listing standards (such as UL508) as a first stop.
 
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