Sparky's Journal

📅 July 31st, 2026

Sparky's Journal: Shims Don't Fix Bad Box Depth

One thing I've started noticing as I spend more time on commercial jobs and dive deeper into the NEC is that a lot of electrical "rules" get passed around without anyone explaining why they exist.

One of those is shimming receptacles.

You'll hear someone say, "Just throw a few shims behind it," and in the right situation, that's completely fine. But the problem is that people start thinking shims can solve every issue involving a crooked or recessed receptacle. That's where the Code draws a line.

What Shims Are Actually For

A listed device shim has one job: align the device so it sits flush and is rigidly supported against the finished wall surface.

If the wall finish is slightly uneven or the device needs a little adjustment to line up with the cover plate, shims make perfect sense. They're there to fine-tune the installation—not to compensate for mistakes made when the box was installed.

That's an important distinction.

The Box Still Has to Be Installed Correctly

Article 314.20 tells us how far a box can be recessed depending on the finished wall.

For noncombustible surfaces like drywall, plaster, tile, or concrete, there is a maximum amount the box is allowed to sit back from the finished surface. If it exceeds that limit, the installation itself is no longer within Code.

At that point, the problem isn't the receptacle.

The problem is the box.

And you can't fix a box installation problem simply by adding more shims behind the device.

The Right Repair

This is where listed box extenders (sometimes called extension rings or box extenders) come into play.

Instead of moving only the receptacle forward, a box extender effectively brings the entire front edge of the electrical box out to the proper depth. That maintains the enclosure, protects the conductors, and gives the device the support it was designed to have.

It's correcting the installation—not hiding it.

That's a huge difference.

The Principle I Keep Seeing Throughout the NEC

As I study more of the Code, one theme keeps showing up over and over:

The NEC doesn't like improvisation.

If a listed product exists for a specific purpose, that's usually the product you're expected to use.

Not because inspectors enjoy making life difficult.

Because someone has already engineered, tested, and listed that solution to perform safely under real-world conditions.

Stacking random materials together might seem like it works today, but the NEC isn't written around "good enough." It's written around proven methods.

Thinking Beyond Memorization

When I first started learning Code, I wanted to memorize articles and section numbers.

Now I'm trying to understand the engineering behind them.

Instead of asking:

"What does the Code say?"

I'm asking:

"What problem is the Code trying to prevent?"

That small shift changes everything.

It makes the Code easier to remember because the rules begin to make sense instead of feeling random.

My Takeaway

This was another reminder that electrical work isn't just about making something fit.

It's about making it fit the way it was designed to be installed.

A few shims can make a receptacle sit perfectly flush.

They cannot make an improperly recessed box magically become compliant.

Sometimes the correct repair takes a few extra minutes.

But doing it correctly the first time is almost always faster than explaining why shortcuts were taken later.

That's one of the biggest lessons I'm learning as I continue working in the field and studying the NEC: understanding why the rule exists is just as valuable as knowing the rule itself.