Plastic extender with knock-outs

[tbluni]

Got a scenario I can not figure out. So, in my garage, on the wall that divides the living space from the garage, is a flush mount dual gang 20 amp GFI outlet and a regular outlet. I recently have taken down the drywall on the ceiling in the garage to patch a leak - and I now find myself wanting to add electrical outlets to the other side of the garage.
My issue is that I can not find a plastic extender that has knock-outs on it - to accept the additional run. Idea being to add a run of 12/2 roamex from the existing outlet (I will bump out the wall, or run in conduit as a sleeve to the ceiling). Any ideas on how to extend the plastic box AND have knock outs for the Roamex?
The metal extender boxes - which do have knockouts - have no way to attach to the plastic boxes I have (they do not accept screws in the corners like the metal ones do).
I don't want to rip out the exiting flush mount box as it goes through double dry wall and old sheathing (garage was clearly an add - on at some point)
Please help
thank you

 

[brewchief]

Look at wiremold products, they should have a dual gang box extender that will work for what you want to do, you may have to use their raceway going up the wall but that should be no big deal.

 

[Norcal]

Either of these will extend a flush box.

http://www.homedepot.com/b/Electric...-Fittings-Boxes-Brackets/N-5yc1vZbohn?Nao=192


http://www.homedepot.com/p/Raco-4-i...s-for-Switch-Boxes-187/202097248?N=5yc1vZbohn

 

[tbluni]

Thanks Norcal..
The issue is that I have no way to attach the double gang metal extender to the plastic box that is installed. The plastic box doesn't have the screw holes in the corners that the metal ones do.


thank you

 

[Mustang51js]

Why can't you just go into the existing plastic box. It should accept more than one wire, or are you trying to surface mount a box in front of old box with Sheetrock still on the wall. Your options are wire mold or snaking it down the wall with a j box up higher.

 

[tbluni]

Im trying very hard to not snaking a new wire in an effort to avoid damaging the insulation in the wall cavity (that wall as it separates the garage from the living space)
Im happy to surface mount the devices - but struggling on how to extend the flush mount plastic box that can also allow for the new Roamex via a knock out.
Is it legal to extend a plastic box with a metal extension (if I could make that work) as the metal extenders all seem to have knock outs
thank you

 

[Hpozzuoli]

I think you might be thinking of a spacer and not an extender. Metal spacers have knockouts. Basically spaces or "extends" your box approx an inch and has knockouts around it. I use them at my laundromats because I have 3 phase and I need the space for the extra wires.