Mounting Motor Disconnects

[big john]

I have a control cabinet (which might at some point have a PLC in it) that will be running two 1.5HP motors that will be operating together, but are not on one machine. Would it be acceptable for me to put the disconnect-switches and overloads for both motors all in that same cabinet?

I know 430.103 says that a disconnect means can be in the same enclosure as the controller. I'm just not too clear if I'd be allowed to put everything in the same box.

Thanks.

-John

 

[pfalcon]

I believe you are looking at your problem from the wrong angle.

It is perfectly permissable to run motors and controllers in separate locations from each other; And to do it out of one common enclosure. It does however become a single machine. If you are working in the enclosure then you must lock out all energy to the enclosure.

Potentially I could wire my entire factory to operate out of one enclosure. LOTO would be horrendous. And I doubt you could sell anyone on it being considered a good practice.

Think hard about what you are going to do when you have to service one motor and run the other one. How are you implementing your LOTO? Will you shut down both machines with the common disconnect? You need a common disconnect for any wiring done in the panel. If you want to service a motor without shutting down the other one then you will need to pay for additional disconnects.

 

[big john]

Pfalcon,

I hear what you're saying and I agree a common disconnect isn't the greatest idea. That's why what I'm hoping to do is put those two totally seperate motor disconnects in the same cabinet. The cabinet would also have a disconnect for the control power. It's not the most elegant design, but it would potentially save a lot of money in materials.

Thanks for the reply.

-John

 

[bobsherwood]

A sump pump or condensate dual pump sequence control comes to mind. They are available with a disconnect switch for each motor, control and starter in the same cabinet.

 

[pfalcon]

Pfalcon,

I hear what you're saying and I agree a common disconnect isn't the greatest idea. That's why what I'm hoping to do is put those two totally seperate motor disconnects in the same cabinet. The cabinet would also have a disconnect for the control power. It's not the most elegant design, but it would potentially save a lot of money in materials.

Thanks for the reply.

-John

You will have to provide a disconnect for the enclosure itself. This is needed for LOTO whenever you service inside the cabinet. I would suggest that the individual motor disconnects be externally mounted so that they may be locked out independantly. Only mount the overloads inside. When you are inside the enclosure you cannot avoid the common disconnect. The independant motor disconnects will be downstream from the enclosure disconnect.

 

[big john]

You will have to provide a disconnect for the enclosure itself.

Are you sure? I think this is technically an "Industrial Control Cabinet" and I couldn't find anything in Article 409 that says I need to be able to simultaneously disconnect all the circuits coming into the cabinet or that the cabinet itself even needs a disconnect means at all.

I think LOTO for the entire cabinet would simply require locking each OCPD that feeds it, which, like I said, isn't elegant, but it works.

What am I missing?

-John

 

[Cow]

I don't know if it'll help or not, but we've used the AB IEC style overloads with the on/off lockable handles on them in our control cabinets. I can't imagine having to disconnect a whole cabinet just to work on one motor.

 

[pfalcon]

Are you sure? I think this is technically an "Industrial Control Cabinet" and I couldn't find anything in Article 409 that says I need to be able to simultaneously disconnect all the circuits coming into the cabinet or that the cabinet itself even needs a disconnect means at all.

I think LOTO for the entire cabinet would simply require locking each OCPD that feeds it, which, like I said, isn't elegant, but it works.

What am I missing?

-John

Sorry for the delay in responding.
Anything that does not power down with the main disconnect is considered a "Remote Energized Source" and has its own special requirements that you don't want to get involved with.
Per NFPA70E you may use an SOP to enter the cabinet for the purpose of locking out an individual motor disconnect, close the panel, service the motor, then re-enter to remove the lock on the motor disconnect.
In either case, the control cabinet MUST have a main disconnect for all power inside the cabinet that is not a "Remote Energized Source". The SOP would provide you a way to enter the cabinet without pulling it just to service a motor.