Do I need a knife switch disconnect on an air compressor?

[JH13]

i have a 480v 250 amp facilities air compressor with the breaker panel in the far end of the room, is it required to put a emergency disconnect along side the compressor? Or would having that breaker "in sight" be acceptable? would adding the disconnect even if not required be a good safety addition?

thanks

 

[kwired]

i have a 480v 250 amp facilities air compressor with the breaker panel in the far end of the room, is it required to put a emergency disconnect along side the compressor? Or would having that breaker "in sight" be acceptable? would adding the disconnect even if not required be a good safety addition?

thanks

Disconnect generally required is more for safety of someone servicing the equipment to be able to turn the power off and have said disconnect within sight while working and not so much an "emergency disconnect".

If breaker in the panel is already within sight, which includes max distance of 50 feet, then it serves that purpose in accordance with NEC.

Many safety policies will have stricter requirements than NEC alone, typically will also want worker to lock that disconnect while working on the equipment even if it is "right there" for easy observation.

An "emergency stop" is required for quick shutdown, primarily to stop the mechanical output of a machine, but often only interrupts controls and not all incoming power to said machine. Such E-stop on an air compressor would only stop the pumping, there would still be pressure in the system (another stored energy hazard) until it naturally is bled out or used up.

 

[JH13]

Disconnect generally required is more for safety of someone servicing the equipment to be able to turn the power off and have said disconnect within sight while working and not so much an "emergency disconnect".

If breaker in the panel is already within sight, which includes max distance of 50 feet, then it serves that purpose in accordance with NEC.

Many safety policies will have stricter requirements than NEC alone, typically will also want worker to lock that disconnect while working on the equipment even if it is "right there" for easy observation.

An "emergency stop" is required for quick shutdown, primarily to stop the mechanical output of a machine, but often only interrupts controls and not all incoming power to said machine. Such E-stop on an air compressor would only stop the pumping, there would still be pressure in the system (another stored energy hazard) until it naturally is bled out or used up.

thank you very much, that was well explained. ill be reviewing my safety policies to make the final decision

 

[Jraef]

...
If breaker in the panel is already within sight, which includes max distance of 50 feet, then it serves that purpose in accordance with NEC.
...

Provided the breaker has a provision for being locked in the Off position. Generally you can buy accessories that can be used to do this if the breaker is not too old and obsolete, but you still have to implement that, you cannot just "trust" that someone will not turn the breaker on while you are working on the machine.

 

[tom baker]

To answer your post title question, no. See definition of disconnecting means, 110.22 Identification of Disconnecting Means, and most importantly, 110.5 Lockable Disconnecting Means.
The rules for motor and motor controller disconnects are in 430.102 and are easy to understand: Disconnect within sight of the controller, and within sight of the motor, with some exceptions. Sometimes the same disconnect can be used for both.
its all about safety, so the worker can shut the power off at the motor, to avoid unsafe shortcuts.
I often will use a non fused knife switch disconnect to install at a motor, it can be a simple way to add a disconnect. But as Jraef pointed out, a CB enclosure can be used if it complies with 110.25

 

[augie47]

Provided the breaker has a provision for being locked in the Off position. Generally you can buy accessories that can be used to do this if the breaker is not too old and obsolete, but you still have to implement that, you cannot just "trust" that someone will not turn the breaker on while you are working on the machine.

Jraef and Tom may add salt to this statement to help me eat the words
As I read 430.102, the "lockable breaker" that is beyond the 50ft "in sight" would apply to the motor
provided there is also a written LOTO procedure but if the controller is also "not in sight from" ie: at your compressor, the breaker lockout does not meet Code. {am I right , guys ?}

 

[Jraef]

Jraef and Tom may add salt to this statement to help me eat the words
As I read 430.102, the "lockable breaker" that is beyond the 50ft "in sight" would apply to the motor
provided there is also a written LOTO procedure but if the controller is also "not in sight from" ie: at your compressor, the breaker lockout does not meet Code. {am I right , guys ?}

Hmmm... so in your fist part, yes, although that is further qualified by being "an industrial installation..." (which is of course open to interpretation).

For the second part, are you posing that the BREAKER is within sight of the compressor, but the CONTROLLER is not? If so, I suppose you are correct.
Breaker in a panelboard, 45ft away and visible from the compressor, but feeding a controller that is around the corner from the compressor to where the breaker is no longer visible, then the breaker as the LO/TO point fails the code requirement for the disconnect means to be within sight of the controller, not just the motor. The exception allowing for an industrial installation etc. is only for the motor disconnect.

 

[tom baker]

The NEC does not tell us what an industrial location is. We know what it isn't...

 

[augie47]

What I attempted to say (while my drugs kicked in ) was that if the controller is mounted on/at the compressor and the breaker does not fit the "in sight from" criteria, a lockable breaker will not meet Code IMO./
The lockable breaker rule is in 430.102(B) reference motors not 420.102(A) controllers.

 

[kwired]

Provided the breaker has a provision for being locked in the Off position. Generally you can buy accessories that can be used to do this if the breaker is not too old and obsolete, but you still have to implement that, you cannot just "trust" that someone will not turn the breaker on while you are working on the machine.

May be good design or even required by safety policy, but if within sight NEC doesn't require locking capability.

 

[retirede]

May be good design or even required by safety policy, but if within sight NEC doesn't require locking capability.

That’s correct, but I’m not sure I’ve ever seen a heavy duty safety switch that isn’t lockable.
Is there anything out there that’s useable as a disconnect at 480V, 250A that isn’t lockable?

 

[kwired]

That’s correct, but I’m not sure I’ve ever seen a heavy duty safety switch that isn’t lockable.
Is there anything out there that’s useable as a disconnect at 480V, 250A that isn’t lockable?

Circuit breakers or molded case switches maybe. Might be included in an enclosure design or able to be field added directly to the breaker though.

If you use an external operator on one the lockable feature is on the external operator, many through the door types you can still turn the switch on when the door is open and won't matter if there is a lock on the external handle. Might need a pliers to assist you but can be turned on.

 

[retirede]

Circuit breakers or molded case switches maybe. Might be included in an enclosure design or able to be field added directly to the breaker though.

If you use an external operator on one the lockable feature is on the external operator, many through the door types you can still turn the switch on when the door is open and won't matter if there is a lock on the external handle. Might need a pliers to assist you but can be turned on.

It’s been years, but I seem to recall that the ones I’m familiar with, the door cannot be opened with the lock applied to the handle.

 

[kwired]

It’s been years, but I seem to recall that the ones I’m familiar with, the door cannot be opened with the lock applied to the handle.

some do, some don't, some have a bypass feature that will let you open the door with use of a tool while the switch is closed. Even run into all of what I said with "safety switches".

 

[retirede]

some do, some don't, some have a bypass feature that will let you open the door with use of a tool while the switch is closed. Even run into all of what I said with "safety switches".

The ones I remember (may have been Square D), with the handle in the at-rest off position, the door could not be opened. You had to press the handle down further past Off to release the latch. If the handle had a padlock on it, you couldn’t press it down to trip the door release. The padlock had to be removed in order open the door.

Early ‘80s - going from my bad memory!

 

[petersonra]

The NEC does not tell us what an industrial location is. We know what it isn't...

I did a quick search. Did not find the term "industrial location" in the NEC. Maybe PDF search missed it.

My search revealed (among other things):

The NEC tells us what a "supervised industrial installation" is, but also uses the undefined terms "industrial installation", "industrial establishment", "industrial laboratory", "industrial building", "industrial equipment", and "industrial premises".

In some cases it uses the term "industrial occupancy", which is a well defined term.

It defines "industrial control panel" and "industrial machine".

There is a place where it defines appliances as being other than industrial, but in another section says something about industrial heating appliances.

 

[Russs57]

No mention of controls or motor starter(s). That could have some bearing.

Since you are on the facilities side, I'd be asking the guys that will service the machine what they want. You do have to meet code but IMHO it should be looked as a minimum requirement.

 

[retirede]

No mention of controls or motor starter(s). That could have some bearing.

Since you are on the facilities side, I'd be asking the guys that will service the machine what they want. You do have to meet code but IMHO it should be looked as a minimum requirement.

All compressors of that size will have integral controls. Most will also have an integral motor starter.
When I was in the business, anything that required a NEMA size 4 or smaller starter was integral with the unit. Most today either have smaller IEC sized starters or VFDs.

 

[kwired]

All compressors of that size will have integral controls. Most will also have an integral motor starter.
When I was in the business, anything that required a NEMA size 4 or smaller starter was integral with the unit. Most today either have smaller IEC sized starters or VFDs.

Small compressor with pressure switch that directly switches the motor, that pressure switch is still considered by NEC to be a motor controller.

 

[Russs57]

Yup, and if it has an integral VFD or starter then I would expect it is has a disconnect already. If that is the case I see no need for a safety switch.

Now if all I got is a pressure switch at the compressor and a starter in a MCC bucket (or hung on the wall) 50' away, then yes I want that safety switch at the unit even if it isn't required by code.