Sub panel feed breaker replacement

[Yale]

The main panel in my garage (SD QO) feeds a sub panel in my basement via a 125A (Q12125) breaker that looks like this:

I need to add a 220 circuit for a planer but the main panel is completely full. Is there any reason that I can't replace this old behemoth with a standard 125A breaker that only takes 2 slots instead of 4? Any idea why this would need 4 slots? It being 220, it already contacts both bus bars. What is the advantage of bridging both sides of the box?

 

[mm08822]

See if you can find a label inside the panel indicating what style of cb and amperage limits there are. Yes there are 2 pole 125 a QO cb's that take only 2 slots. They are $$$. Another option is lowering down to a 2 pole 100a cb for about 1/2 the price of the 125a.

The reason why this cb connects to 4 buss stabs is that either the cb connecting hardware couldn't handle the 125a alone or the buss stabs couldn't or a combination of the 2.

Someone can probably tell you the history of QO's about evolving from 4 stab to 2 stab versions.

Also check the replacement cb can handle the wire size of your feeder.

 

[mm08822]

The CB you have is of a Q1 series cb - label indicates that. Q1s are obsolete. QOs replace them now apparently.

Does the label inside your panel indicate "NQO" panelboard?

 

[Yale]

Thanks for the info, mm. The label on the inside of the door lists it as a QOC20MW225, if that helps. I'm tempted to go the 100A breaker route as the subpanel that it feeds served quite a few 220 appliances (WH, oven, dryer, 4 baseboard heaters) that have been removed and/or converted to gas so the actual load is a lot less than it was originally.

 

[mm08822]

I believe that part number is for the cover only.

In the panel back box there might be a label with something similar to "QON20-40MW200-1 Series L8". Unless a label detail indicates otherwise, I'd assume the QO2100 is permitted based upon the above screenshots from SQ D.

 

[Yale]

I found the tag on the inside of the panel. It reads QOB30MW200 Series L8. Google doesn't have much information for that model number.