# Line Isolation vs Control Isolation



## Harbinger (Jun 27, 2008)

So I was working a shut down at a local hydro electric station last week and was tasked with cleaning out the two MCCs and retorquing all the lugs and tightening all the connections. I opened the two 600V 800A disconnects and checked the wiring diagram to see how it was controlled. Sure enough it had a remote close button up in the control room. The way this unit was wired was such that removing the upstream fuse would still not isolate the load and pulling both upstream fuses would disconnect power for the entire site. I did not know how to mechanically lockout this particular breaker and the plant operators had no idea. So I disconnected the remote close button and got the job done.
THe disconnect was a cutler hammer 1200A push button(don't have part numbers) but short of unbolting it from the bus is there a way to mechanically isolate this to achieve "line isolation".
My only concern was reconnecting the remote close, if some dipstick left a tool in the cabinet across a phase and I got a poorly timed case of the shakes the switch could close with poor me standing in front of the open cabinet...
So I got all anal and visually inspected every square inch before reconnecting, safe but very time consuming. Any ideas?
Oh yeah this place has a back up generator but no transfer switch, they rely on the PLC as a transfer switch!


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