110.72 - Cabling Work Space (Or: "How Not to Get Stuck Like a Sausage in a Manhole")

The Real Deal

Listen up, because this one's about not getting wedged into underground spaces like you're trying on your high school jeans. When you're working in manholes, vaults, or any confined space where cables are hanging out, the Code says you need actual room to work – not just "suck it in and hope" clearances.

Here's the breakdown:

If you've got cables on BOTH sides of you:

• You need a minimum 3-foot-wide work space. That's 36 inches of "please don't let me get stuck" room. Think of it as enough space to swing your elbows without karate-chopping a 15kV feeder.

If cables are only on ONE side:

• You can get away with 2½ feet (30 inches). Still tight, but you're not doing the underground electric cable sandwich.

Vertical headroom:

• You need 6 feet minimum of standing room. Because crawling around like a mole person isn't in your job description – unless the opening itself is within 12 inches of the side wall. Then apparently, being a contortionist is acceptable.

The Exception (AKA "The Light Duty Loophole")

Now, if your manhole ONLY contains the wimpy stuff – fiber optics, fire alarm circuits, Class 2/3 signaling, or Class 4 circuits (basically everything that won't turn you into a lightning rod) – you can squeeze one dimension down to 2 feet. BUT – and this is a big but – the OTHER dimension has to make up for it so the total adds up to at least 6 feet.

So you could have a 2-foot by 4-foot space, or 2½ by 3½ – whatever, as long as the math works and you're only dealing with low-energy cables that won't bite back.

Translation: The Code is saying, "Look, if it's just telecom stuff, we'll let you work in a slightly smaller coffin. But if there's real power down there, you better have room to move when things go sideways."

Key Takeaways (The Stuff That Actually Matters)

• 3 feet wide minimum when cables are on both sides of the work space
• 2½ feet wide minimum when cables are only on one side
• 6 feet of headroom is mandatory (unless the opening is within 1 foot of the wall)
• Exception for wimpy circuits: Can reduce one dimension to 2 feet IF the other dimension compensates (sum = 6 feet minimum)
• Exception ONLY applies to: fiber optic, power-limited fire alarm, Class 2/3 signaling, and Class 4 circuits
• This is about confined spaces – manholes, vaults, cable pits – not your typical pull box

Real-World Scenarios (Why This Rule Exists)

Scenario 1: The Utility Vault Tango

You get called to a commercial building where someone complained about data cables. You pop the manhole cover and see 4-inch power feeders on one side, telecom cables on the other, and exactly 28 inches of space in between. You climb down, realize you can't turn around without your back touching a 480V feeder, and immediately climb back out to call the engineer.

Why it matters: That vault is a Code violation waiting to hurt somebody. With cables on both sides, you need that full 3 feet. This isn't about comfort – it's about having enough room to work safely when something sparks, shorts, or decides to have a bad day.

Scenario 2: The Fiber-Only Forgiveness

Data center job. You're installing a new fiber run through an existing manhole. Inside: nothing but fiber optic cables and a few Class 2 fire alarm circuits. The space measures 2 feet by 4 feet (total = 6 feet). Your foreman starts having a panic attack about 110.72 until you show him the exception.

Why it matters: The Code recognizes that fiber and low-energy circuits won't kill you if you bump into them. You still need adequate workspace, but the requirements are slightly relaxed because the hazard level is way lower. It's the difference between working near a sleeping kitten versus a hungry tiger.

Scenario 3: The Six-Foot Shuffle

You're roughing in underground utilities for a parking lot. The engineer spec'd manholes that are 2½ feet by 2½ feet (total = 5 feet). "It's close enough," he says. You politely explain that 5 is not 6, and even with the exception, you need that full 6-foot total dimension. He gets mad. You show him 110.72. He fixes the drawings.

Why it matters: Inspectors can do math. That extra foot isn't arbitrary – it's the difference between being able to maneuver tools, your body, and equipment versus being wedged in there like a cork in a bottle when something goes wrong.

What to Study (Exam Prep)

High-probability exam questions:

1. The 3-foot vs. 2½-foot rule – Know which applies when cables are on both sides vs. one side
2. The exception calculation – They LOVE asking about that 2-foot minimum with a 6-foot total
3. What circuits qualify for the exception – Memorize that list: fiber, power-limited fire alarm, Class 2/3, Class 4
4. Vertical headroom requirement – 6 feet is the number, and when the exception applies (within 1 foot of the wall)
5. Where this applies – Manholes, vaults, and similar confined underground spaces (not regular enclosures)

Typical exam question formats:

• "A manhole contains medium voltage cables on both sides. What is the minimum width required?" (Answer: 3 feet)
• "A vault contains ONLY fiber optic cables. The work space is 2 feet in one direction. What is the minimum required dimension in the other direction?" (Answer: 4 feet, so the sum equals 6)
• "Which of the following does NOT qualify for the reduced workspace exception?" (They'll throw in a power circuit – pick that one)

Pro tip: On the exam, if they mention HIGH VOLTAGE or POWER circuits, you're doing the full 3-foot clearance. If it's all wimpy communication stuff AND they specifically mention the exception, then you can play the 2-foot + 4-foot game.

The Bottom Line

The NEC isn't trying to make you claustrophobic – it's trying to keep you from becoming a statistic. Whether you're pulling cable, troubleshooting faults, or doing maintenance, you need room to work. This section is basically the Code saying, "Hey, if you can't move freely around energized equipment in a hole in the ground, maybe we shouldn't put you in that hole."

Remember: Three feet when surrounded, two-and-a-half when not, six feet of headroom, and don't get creative with the math unless it's low-voltage wimpy stuff.

Now go forth and don't get stuck in any manholes. Your back, your sanity, and your lawyer will thank you.