Working Clearance at Safety Switches

[aaronbailey52]

Looking for some input on the working clearance requirements about a safety switch/disconnect. Situation is a 7.5 hP motor inside of a cooling tower enclosure. There is a disconnect adjacent to this motor, inside of the enclosure. The fan belt from the motor is at the same height as the handle of the disconnect and at its farthest point is 15" away.

Now, the motor is controlled by a VFD with lockable disconnect. So, circuit breaker feeds VFD. VFD feeds disconnect switch. Disconnect feeds motor.

Is it reasonable to consider that the disconnect is unlikely to be operated or adjusted when energized, considering that power can be locked out at the VFD? Cooling tower is within sight of the VFD at about 10' away.

I would also note that the install instructions for the cooling tower call for the disconnect on the outside of the enlosure.

The disconnect does in no way, shape, or form meet working space requirements, if it is considered to require examining while energized.

Thanks

 

[lielec11]

Looking for some input on the working clearance requirements about a safety switch/disconnect. Situation is a 7.5 hP motor inside of a cooling tower enclosure. There is a disconnect adjacent to this motor, inside of the enclosure. The fan belt from the motor is at the same height as the handle of the disconnect and at its farthest point is 15" away.

Now, the motor is controlled by a VFD with lockable disconnect. So, circuit breaker feeds VFD. VFD feeds disconnect switch. Disconnect feeds motor.

Is it reasonable to consider that the disconnect is unlikely to be operated or adjusted when energized, considering that power can be locked out at the VFD? Cooling tower is within sight of the VFD at about 10' away.

I would also note that the install instructions for the cooling tower call for the disconnect on the outside of the enlosure.

The disconnect does in no way, shape, or form meet working space requirements, if it is considered to require examining while energized.

Thanks

Maybe a dumb question, but if your VFD is equipped with a lockable disconnect switch and is in viewing distance only 10ft. away why bother with another disconnect at all? Why not go from the load side of the VFD to the motor and be done?

 

[aaronbailey52]

Maybe a dumb question, but if your VFD is equipped with a lockable disconnect switch and is in viewing distance only 10ft. away why bother with another disconnect at all? Why not go from the load side of the VFD to the motor and be done?

Well, it's shown on the drawings, so it was put in. Now have to make sure it's right.

 

[ptonsparky]

Maybe a dumb question, but if your VFD is equipped with a lockable disconnect switch and is in viewing distance only 10ft. away why bother with another disconnect at all? Why not go from the load side of the VFD to the motor and be done?

Not a dumb question, but what it still doesn't answer his. I have installed roof top ventilation equipment that has a disconnect just under the cap and is there for servicing the belts etc. Factory installed. Now if I put a small disconnect under the cap of a similar unit do I need the 30" and 36"?

 

[steve66]

From the photo, it looks like you would be crazy to be standing in front of the disconnect with the power on and the fan running.

It looks like if you stood up a little too straight, you would at least get haircut.

If thats true, I would say working space not required.

 

[petersonra]

I don't see how you could ever safely work in there with it energized so it seems like a moot point to me.

 

[Nom Deplume]

Putting a disconnect on the load side of a VFD isn't a good idea unless there is an early break aux switch wired to shutdown the VFD when opened.
Opening the load side while under load can damage the drive.

There is an exception to 430.102(B)(2) Exception (a) and Informational Note 1 that might help you.

 

[petersonra]

Putting a disconnect on the load side of a VFD isn't a good idea unless there is an early break aux switch wired to shutdown the VFD when opened.
Opening the load side while under load can damage the drive.

There is an exception to 430.102(B)(2) Exception (a) and Informational Note 1 that might help you.

how is he ever going to operate the switch while the VFD is running? he can't go in there while the VFD is running. It would be unsafe to do so.

 

[Aleman]

Putting a disconnect on the load side of a VFD isn't a good idea unless there is an early break aux switch wired to shutdown the VFD when opened.
Opening the load side while under load can damage the drive.

There is an exception to 430.102(B)(2) Exception (a) and Informational Note 1 that might help you.

Agree with you. But some of these VFD's seem to handle it ok. AB's seem to pretty much bulletproof. Hitachi's will run with load disconnected without self destructing. Not a good practice but
maybe not as bad as they say. Just the same I use aux switches on all new installs and am upgrading the others as I go.

For the OP's question, in your situation as shown I would rely on a disconnect pre motor drive. Seems impractical to put a disconnect in that small enclosure. Especially when the controls are that close.

 

[petersonra]

For the OP's question, in your situation as shown I would rely on a disconnect pre motor drive. Seems impractical to put a disconnect in that small enclosure. Especially when the controls are that close.

It is a potentially dangerous enough situation being in that space if the fan were to come on that maybe they installed the disconnect switch to make the repair guy feel better when he goes inside. He can open the switch and it is right there under his control.