Of the tools mentioned, the Dremel will be the best one. Too much vibration on a multi tool, and a grinder....well, you know. You have the extension inside the hole, it appears. Leaving it on the outside would be fine. Can you do that?

 

It's not going to make a difference if I leave the extender outside the box by trimming it. The extender is tapered and fits through the mud ring opening nicely but the widest outside will not bottom to the mirror because it is too wide (by a small amount). I think Carlon makes a blue extender but not tapered, so it probably doesn't even fit at all.

 

That is not a plastic box extender it is a plastic box.
None of what you propose is legal because your using parts outside their design parameters.
The right way cut a hole big enough to get metal box extenders back to the box. This will be ugly and a lot of 4 lettered adverbs will be used. Then have or find a mirrored cover for the outlet to trim the job out.

 

That is an Arlington BE-1 box extension. It is made to slide into the box.

 

Split the entender and slip it in.

 

Oh never thought of that. I may not even need to split it all the way may be a bird beak at the front one inch or so. Will try the Dremel first if that doesn't work this will be plan B. Thanks!

 

I use a diamond disk with my dremel. Never tried to cut glass but has lasted through many metal cutting jobs.
Bud

 

Is there any other location you can put receptacles? then put a blank cover over the subject receptacle location. I think there is the danger of breaking the mirror by the vibration caused by plugging and unplugging things at the subject receptacle locaiton.

 

Not really. It's an L shaped counter, mirror runs the entire width and height. Both receptacles are on the mirrored wall. They have been there since 2007 construction, I don't think the mirror will break, the devices are attached to the mud ring, the mud ring to the metal boxes and the metal boxes to the framing. Shouldn't be a lot of stress on the receptacle especially since I am not using tamper resistant ones.

 

A novel approach If I may.

Remove enough bulk from the extender with the Dremel, to clear the obstruction.

That way there is no chance of breaking the mirror with a tool.

Make the extension a little bit thinner at the proper spots to clear the obstruction.

ED

 

A novel approach If I may.

Remove enough bulk from the extender with the Dremel, to clear the obstruction.

That way there is no chance of breaking the mirror with a tool.

Make the extension a little bit thinner at the proper spots to clear the obstruction.

ED

I will try, but the plastic extender is quite thin, may be less then 1mm so any removal will basically break it. But I will try with a Dremel first, I think I may have some engraving tips I might try on the mirror and see if it's able to just shave off a bit. I may shave a hair off the extender at the same time. If that doesn't work Jim Port's advice to split the extender is in my back pocket.

 

Cut the extender and take 1/8" out of the center and run a tape around it to hold it while you install it.

 

Put the cover back on and leave it be.

 

No way would I try to shave the mirror!
Don't look for a problem that doesn't exist.
Code says the box has to extend beyond flammable materials which the space beyond the wall is not.

 

NEC code says a "maximum" recess of 1/4". and then only in non-flammable materials. Anything over 1/4" needs a box extension

 

I think I'd use a heat gun on the plastic extender (but not while its next to the mirror) in order to heat it up and deform it just enough that you can push it back flat into the mirror cutout. Probably not NEC approved to alter the extender but it's better that ruining the mirror.

 

OK some good news. My plan was to give it a try on shaving the mirror's left edge at the corners with a Dremel. I have a cone shaped bit and a diamond bit.

Took some patience but it worked and I just needed a little around 1/16" or so. Here are the slightly shaved corners.

I was able to bottom the extender into the metal box mud ring opening.

 

That's great !! How many layers of sheetrock is there????

 

Two layers of sheetrock.

 

Looking good, A cover to hide the "funky", and you are good to go.

ED