OT: Rotary disconnects that lock door when locked out

[kolyur]

I've noticed a strange behavior with certain rotary disconnects. We all know that, if installed correctly, the disconnect interlocks with the door such that it cannot be opened while in the "on" position unless the defeater is pushed (if equipped with one). No problem there.

But some rotary disconnects seem to have an additional "feature" in that they prevent the door from being opened when the disconnect is off *and* locked out. I fail to see any logic to this arrangement. Suppose Bubba #1 notices an electrical problem with a machine towards the end of his shift, so he shuts it off and locks it out. Bubba #2 on the next shift is sent down to work on it. Instant problem--he can't even open the panel door! His only option is to remove Bubba #1's lock (a major no-no at most places), open the panel, then reapply the lock.

I encountered this today with an Allen-Bradley 194R-J60-1753 disconnect and 194R-PY handle. There does not seem to be any way to disable the door lock (although, according to the manual, by removing a couple tabs you can surprisingly allow the disconnect to be padlocked in the "on" position--wow). The funny thing is that there is no mention of this function in the manual. I did find a tech note on the AB knowledgebase that does confirm this is working as designed.

I looked at the datasheets for several other brands of rotary disconnects, and couldn't find any mention of whether this restriction exists. Can anyone comment as to how prevalent this is with rotaries? Also, suggestions for 60A class J fused disconnects without it would be appreciated. I mainly work with flange type disconnects that don't have this bizarre feature.

 

[LadderLogic]

I think this makes sure no one can open the door and rotate the disconnect shaft into "on" position while there is a lock-out and someone is working on the machine.

 

[TWS]

We only specify flange mounted disconnects. It seems that every door mounted rotary disconnect has its own quirks and idiosyncrasies.

 

[ASF]

I think this makes sure no one can open the door and rotate the disconnect shaft into "on" position while there is a lock-out and someone is working on the machine.

This is exactly the reason. If the isolator is mounted to the gear plate with an extension handle protruding through the door, and you can open the door, you immediately remove the "locked" part of the isolator from the part that switches, rending the lockout useless.

This is just one more reason I avoid those style of isolators wherever possible. It can be locked out, OR you can work on the panel, but you can't do both. You have to go and isolate upstream.

 

[Puddle]

I like the ABB switchgear. OT range for non-fused, OS range for fused. I've fitted quite a few with (so far) no issues at all and something that I like (which may be against policy on some sites) is that they have an over-ride button in the handle so you can open the panel for fault-finding without shutting the machine down.

 

[joseph_e2]

The newer rotary switches I've used (from Socomec and A-B) have lockout points on the switch itself in addition to the one on the handle. I think one of them may have been an optional add-on, but others came with it.



I far prefer the flange-type switches but availability has been very spotty.

 

[kolyur]

I think this makes sure no one can open the door and rotate the disconnect shaft into "on" position while there is a lock-out and someone is working on the machine.

Yes I'm sure this is the reason, but the panel could be separately locked to prevent unauthorized access if this is a concern. Personally it seems equally dangerous to have a setup where the lock has to be removed--if only temporarily--during maintenance activities just to access the panel.

The newer rotary switches I've used (from Socomec and A-B) have lockout points on the switch itself in addition to the one on the handle. I think one of them may have been an optional add-on, but others came with it.

This is the way to go. I found that AB has an accessory for their rotary disconnects (194R-PLA1) that attaches to the front face and allows the shaft itself to be locked out. I'll be sure to get that option from now on.