NEC 110.70: Walk-In Electrical Closets (AKA "Don't Build a Coffin")

The Plain-Talk Breakdown

Alright, listen up. This section is about those big electrical rooms and enclosures you can actually walk into—you know, the ones where you're shoulder-to-shoulder with 480V gear while trying not to pee your pants.

Here's what Big Code is telling us: If you're building an electrical room that people need to enter, don't make it so cramped that the next guy has to work on live equipment while doing yoga poses. Give them enough space to actually work without becoming a statistic.

These spaces need to be big enough that when somebody inevitably has to troubleshoot, adjust, or fix something while it's still hot (and we all know that happens), they can do it without their nose touching a bus bar. Plus, you need enough room to pull wire in and out without stripping the insulation off on sharp edges like you're peeling a banana.

Think of it this way: if your electrician needs to be a contortionist to work in there, you built it wrong. The NEC wants safe work space, not a game of "Operation" where losing means a trip to the burn unit.

The Exception (Industrial Get-Out-of-Jail Card):

Now, if you're in a big industrial facility with actual qualified people babysitting the electrical system 24/7—not just a maintenance guy who also mows the lawn—you might get to design things your own way using "engineering practice." But the AHJ (that's your inspector, for you first-years) can still say "show me the math," and you better have fancy drawings to back it up.

Key Takeaways (The Stuff That Matters)

Technical requirements you better not forget:

Walk-in enclosures must provide SAFE WORK SPACE around live parts that might need servicing while energized
- Not "technically possible" space
- Not "if you suck in your gut" space
- SAFE space
Conductor installation space is mandatory
- Must allow installation AND removal of conductors without damage
- Wire insulation can't be scraped off during installation (looking at you, retrofit jobs)
These enclosures must comply with ALL of Part VI requirements (110.70 through 110.79)
- Workspace dimensions (110.26)
- Working clearances
- Lighting and headroom
- The whole nine yards
Industrial Exception Requirements:
- Only applies under maintenance and supervision conditions
- ONLY qualified persons monitoring the system
- Must follow appropriate engineering practice (not "Bubba's best guess")
- AHJ can demand design documentation—have it ready

Real-World Jobsite Scenarios

Scenario 1: "The Telephone Booth Switchgear Room"

You bid a data center job, and the architect designed a "compact" electrical room that's basically a broom closet with delusions of grandeur. The 800A switchgear barely fits, and there's about 18 inches between the gear and the wall.

Your foreman takes one look and says, "How's anybody supposed to work in here?"

Why 110.70 matters: When that gear needs maintenance at 2 AM (and it will), the tech needs safe working clearance—not a chance to play "Operation" with 480V. This section backs you up when you tell the GC, "Nope, tear down that wall or move the gear. Code says so." The space needs to meet 110.26 working clearances PLUS have room to work safely. This isn't negotiable.

Scenario 2: "The Wire-Scraping Special"

You're pulling 500 kcmil feeders into a main distribution room through a knockout that's barely big enough. Every time you pull, you're hearing that lovely scraping sound of insulation being shaved off like Parmesan cheese.

Why 110.70 matters: That second sentence isn't just a suggestion—it's a requirement. The enclosure must allow conductor installation without damage. Those scraped conductors? That's a failed inspection waiting to happen, and a potential fault down the road. If you can't get the wire in cleanly, the room wasn't built to code. Time to install a proper pull box or make the opening bigger.

Scenario 3: "But We've Always Done It This Way"

You're working at a chemical plant where everything is custom-engineered. The electrical engineer wants to design a walk-in equipment room that doesn't quite meet standard workspace clearances, claiming the industrial exception applies.

Why 110.70 matters: Hold up, cowboy. That exception isn't a free pass. You need QUALIFIED personnel monitoring the system (not just a maintenance department), it has to be designed with actual engineering (calculations, drawings, the works), AND the inspector can still say "show me your paperwork." If you can't check all those boxes, you're building it to the standard rules. Period.

What to Study (Exam Prep Focus)

When you're sitting for your Journeyman or Master's exam, here's what they LOVE to hit you with:

High-Probability Test Topics:

The basic requirement: Know that walk-in enclosures must provide safe work space—they'll give you a scenario and ask if it complies
Conductor damage prevention: Expect a question about whether conductor insulation damage during installation is acceptable (hint: it's not)
What sections apply: Know that these enclosures must comply with "this part" (meaning Part VI of Article 110—sections 110.70-110.79)
The industrial exception conditions:
- Only qualified persons
- Maintenance and supervision requirements
- Engineering practice required
- AHJ can demand documentation

How They'll Test You:

Scenario question: "An electrical room is designed with equipment that requires energized maintenance, but the workspace is only 2 feet deep. Does this comply with 110.70?"
- Answer: No—must provide SAFE work space per this section and meet 110.26 clearances
True/False trap: "Walk-in enclosures only need enough space to fit the equipment, not additional working space."
- Answer: False—safe WORK SPACE is required
Application question: "Can scraping of conductor insulation during installation be accepted if it's minor?"
- Answer: No—110.70 specifically requires installation without damage to conductors or insulation

Study Tips:

Link this section with 110.26 (working clearances)—they work together like peanut butter and jelly
Remember the difference: 110.26 gives you the DIMENSIONS; 110.70 says walk-in spaces MUST comply with those dimensions
Don't get fooled by the industrial exception—it's narrow and has specific requirements

The Bottom Line

110.70 is the NEC's way of saying: "Don't build death traps." If someone can walk into it, they need room to work safely. Your back, your life, and your license will thank you for building it right the first time.

Now get out there and build spaces people can actually work in without needing a chiropractor afterward.

Stay safe, stay legal, and for the love of Mike Holt, give people room to work!