Disconnect Switch for Air Comp.

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aanvari3

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Okay, so we bought an air compressor that comes with its own plc, starter, etc. It has an emergency stop button on it as well as start, stop, reset. The circuit breaker the starter is fed from is in another building. Do we have to put an additional fused disconnect switch near the air compressor so that it is "in view" of it? Or is the circuit breaker (that is off an MCC) enough? NEC figure 430.1 is a little unclear to me. I take it the "stop" button on the controls of the compressor isn't considered a disconnect from the power?

Like this :
disconnect.jpg


Is the middle disconnect switch and fuse required?
 

augie47

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You have possibly opened up a whole bag of worms. The"other building" scenerio might be a problem. Does this building already have power ?
If so you need to check Art 225.30 to see about adding a second power source.
In any event Art 225 will be one of your guides as far as disconnecting means at the second building and I would start there (Art 225).

In addition, the stop button will not suffice as the "in sight" disconnect for a motor controller. (Art 430.102)
 
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aanvari3

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What if our Motor Control Center the motor is being fed from has a Lockout/Tagout system? Then would we not need a disconnect switch at the unit?
 

don_resqcapt19

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What if our Motor Control Center the motor is being fed from has a Lockout/Tagout system? Then would we not need a disconnect switch at the unit?
There is no exception to the code rule that requires a disconnect within sight of the motor controller (starter) for a system rated at 600 volts or less. 430.102(A).
 

aanvari3

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What about 430.102(B)(2)(b) that states "In industrial installations, with written safety procedures, where conditions of mainenance and supervision ensure that only qualified persons service the equipment." Then underneath that if has "FPN No.1: Some examples of increased or additional hazard include motors rated in excess of 100 hp, and motors located in hazardous locations."

In the 2008 NEC it says "Per the exception to 430.120(B), the disconnecting means may only be out of sight of the motor if the disconnecting means complying with 430.102(A) is individually capable of being locked in the open position and meets the criteron of either (a) or (b) of the exception. If locating the disconnecting means close to the motor location and driven machinery is impracticable due to the type of machinery, type of facility, lack of space, or any increased hazard to persons or property, the disconnecting means is permitted to be located remotely."

Reasons why i don't want the switch at the motor :
1) In a Class I, Div II area
2) The Motor is 125 HP
3) The circuit breaker in the MCC is capable of lockout/tagout.
4) Only qualified people will operate the machinery.
 
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raider1

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You must still have a disconnecting means within sight from the controller capable of being locked out. The exception you are quoting only applys to the motor disconnect not the disconnect for the controller.

Chris
 

don_resqcapt19

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What about 430.102(B)(2)(b) that states "In industrial installations, with written safety procedures, where conditions of mainenance and supervision ensure that only qualified persons service the equipment." Then underneath that if has "FPN No.1: Some examples of increased or additional hazard include motors rated in excess of 100 hp, and motors located in hazardous locations."

In the 2008 NEC it says "Per the exception to 430.120(B), the disconnecting means may only be out of sight of the motor if the disconnecting means complying with 430.102(A) is individually capable of being locked in the open position and meets the criteron of either (a) or (b) of the exception. If locating the disconnecting means close to the motor location and driven machinery is impracticable due to the type of machinery, type of facility, lack of space, or any increased hazard to persons or property, the disconnecting means is permitted to be located remotely."

Reasons why i don't want the switch at the motor :
1) In a Class I, Div II area
2) The Motor is 125 HP
3) The circuit breaker in the MCC is capable of lockout/tagout.
4) Only qualified people will operate the machinery.
I didn't say you can't have a remote lockable disconnect for the motor. I said you can't have a remote lockable disconnect for the motor controller (starter). There are two independent rules in 430.102. 430.102(A) is for the required controller disconnect and 430.102(B) is for the required motor disconnet. You must stasify both rules, although by using the exception in 102(B), the controller disconnect can ofter serve both purposes.

I see Chris beat me to this answer.
 

don_resqcapt19

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...
Reasons why i don't want the switch at the motor :
1) In a Class I, Div II area
2) The Motor is 125 HP
3) The circuit breaker in the MCC is capable of lockout/tagout.
4) Only qualified people will operate the machinery.
So you have a compressor with a size 5 explosionproof starter and PLC suitable for Class I, Division 2? (assuming this is the compressor in the original post)
 

aanvari3

Member
Yes, the starter and PLC are in an enclosure with a Z-purge.

I'm confused, I only have 3 power cables going to the motor from my main circuit breaker. The starter which is in the same enclosure as the motor, gets its power inside the enclosure, so The starter is located inside the enclosure and goes straight to the motor, so i don't see how i'd put another disconnect between the starter and motor. The starter indicates it has a bypass so I suppose that would be its disconnect.

EDIT: Oh, so your saying that since the same cables go from the circuit breaker to the starter to the motor, since the starter is in there there needs to be a disconnect in sight?
 
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don_resqcapt19

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...
EDIT: Oh, so your saying that since the same cables go from the circuit breaker to the starter to the motor, since the starter is in there there needs to be a disconnect in sight?
Yes, 430.102(A) requires a disconnect within sight of the starter and there are no exceptions for your application.
 
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