Relay Terminology - S.O.? M.O.?

[Dark Sparky]

I am familiar with the foundational relay terminology N.O. (normally open) and N.C. (normally closed). Ran across an old 13.2 kV diagram for some 13.2 kV metal enclosed switchgear - which uses those NO & NC abbreviations, along with "S.O." The NO/NC/SO terms are used adjacent switches in the bus and switches in the feeder breakers for this gear. I also saw another abbrev. in similar context recently, which I can't find a the moment - I believe it was M.O. or M.C. I believe I also may have seen S.C. somewhere. The places where "S.O." is shown are bus and feeder switches which show motors (standard motor with 2 wings symbol) next to them. I've searched online, but can't find anything that might explain what these mean. Can someone shed light on what S.O. would stand for in this context? How about the ephemeral SC/MO/MC which I believe I saw on a similar diagram? Thanks!

Also - the bus/feeder switches which show SO use it in combination with another abbrev. So the bus & feeder switches either say "N.O., S.O." or "N.C., S.O." The way it's written (one abbrev. above the other) seem to imply that both terms apply to those switches.

 

[jim dungar]

One problem with the simple NO NC is what is the normal position? A contact that is normally open on the shelf may be held closed when it is installed. So it is not uncommon to see additional descriptors, especially for limit switches and timers.

However I do not know what your SO and MO would stand for.

For switchgear we often have MOC and TOC switches (mechanism operated and truck [racking mechanism] operated switches.

Whose brand of gear is this?

 

[ron]

MO Manually operated
MC Manually closed

 

[petersonra]

I have seen SC and SO before. It meant "shown closed" and "shown open". No idea if that is what it means in your case. I always thought it was kind of confusing because it really was not clear to me exactly what they meant by it.

 

[synchro]

I have seen SC and SO before. It meant "shown closed" and "shown open". No idea if that is what it means in your case. I always thought it was kind of confusing because it really was not clear to me exactly what they meant by it.

Thanks for that info. I don't know for sure, but I suspect SC "shown closed" and SO "shown open" may be used when illustrating different states that can be taken by relay logic during usage. So a "shown" position could be the same or opposite position as the normally closed or open position, depending on the particular state that the sequential logic is in. In this case I'd expect that more than one schematic version would be provided to illustrate the different control logic states that can be taken.

 

[Jraef]

S.O. = Shunt Open
S.C. = Shunt Close
M.O. = Motor Open
M.C. = Motor Close

Has to do with spring charged mechanisms on MV and HV power devices like Power Circuit Breakers.

 

[Dark Sparky]

Thanks all - much appreciated. Love the knowledge on this forum. Your comments helped.