NEC 110.73: Equipment Work Space (Or "Why That Manhole Better Not Be a Coffin")

The Street Talk Version

Alright, listen up. You know those underground vaults, manholes, and utility closets that make you feel like you're working in a concrete burrito? Yeah, those. The Code says if you're stuffing live electrical equipment down there that somebody's gonna have to mess with while it's HOT, you better give 'em room to work without becoming a statistic.

Here's the deal: If it's 1000V or less (AC) or 1500V or less (DC), you gotta follow all the work space rules from 110.26 – same clearances you'd need above ground. You know, the "don't make me work in a phone booth" distances.

If you're playing with the big boy voltage (over 1000V AC or 1500V DC), then you jump up to 110.34 requirements. That's the high-voltage workspace stuff with even MORE room because, well, higher voltage has a longer reach and a worse attitude.

And here's a freebie: If that manhole cover weighs more than 100 pounds (about 45 kg for our metric friends), the Code considers it heavy enough to keep the unauthorized folks out. So you can check off the "secured access" requirements in 110.26(F) and 110.34(C) without adding a padlock. Because let's face it – if Cousin Eddie can't deadlift it, he's probably not getting in there to "see what this wire does."

Key Takeaways (The Stuff That Matters)

🔧 Voltage threshold matters:

≤1000V AC or ≤1500V DC = Follow 110.26 workspace requirements
1000V AC or >1500V DC = Follow 110.34 workspace requirements

🔧 It only applies to equipment with:

Live (energized) parts
That will likely need examination, adjustment, servicing, or maintenance
While still energized (not de-energized and locked out)

🔧 Location-specific:

Manholes, vaults, or other enclosures designed for personnel access
Underground or enclosed spaces where workers enter

🔧 The 100-pound rule:

Manhole covers ≥100 lbs automatically satisfy the "secured access" requirements
No additional locks or securing methods needed (gravity is your friend)

Real-World Scenarios (Why This Rule Exists)

Scenario 1: "The Pretzel Position"

You get called to troubleshoot a 480V transformer in a utility vault. You climb down and realize the genius who installed it left about 18 inches between the energized bus bars and the wall. You're now doing electrical work in a yoga pose that would make a contortionist cry, with your face uncomfortably close to live copper. That's a 110.26 violation, brother. You need 3 feet of clearance (minimum) to work safely. This section says even though you're underground, the space requirements don't go away.

Scenario 2: "The Medium-Voltage Surprise"

A developer wants to save money by shrinking a 13.8kV switchgear vault. "It's underground! Who cares?" Um, the electrician who has to go in there cares. And so does 110.73. Because it's over 1000V, you need 110.34 spacing – which means more room, better egress, and proper illumination. You show them this section, they grumble, then they pour more concrete. Your future self thanks you.

Scenario 3: "The 100-Pound Solution"

Inspector shows up and asks, "How are you securing this manhole per 110.26(F)?" You're about to panic about padlocks and hasps when you remember this section. "That lid is cast iron and weighs 120 pounds. Per 110.73, that's considered secured." Inspector nods, checks his box, and moves on. You just saved $200 in hardware and an hour of installation. Buy yourself lunch.

Scenario 4: "The Maintenance Reality Check"

Engineer specs a vault for a 600V distribution panel but makes it so tight you can't open the panel door all the way. "But it's de-energizable!" he protests. You point to 110.73: It says equipment "likely to require examination, adjustment, servicing, or maintenance while energized." Buddy, when this thing trips at 2 AM on a Saturday, you think anyone's doing a full shutdown and LOTO procedure just to reset a breaker? Nope. They're going in hot. Make it big enough.

What to Study (For the Test)

When you're staring at your Master's or Inspector's exam and this topic comes up, here's what they love to ask:

1. The Voltage Breakpoint (They LOVE this one)

Know that 1000V AC / 1500V DC is the dividing line
Below = Article 110.26 rules
Above = Article 110.34 rules
They'll give you weird voltages like 999V or 1001V to trick you

2. The 100-Pound Manhole Cover Rule

Memorize: 100 lbs or 45.4 kg
Know it satisfies 110.26(F) (low voltage) AND 110.34(C) (high voltage)
This is FREE POINTS on a test – don't miss it

3. What Equipment Qualifies

Must have "live parts" (not just a sealed enclosure)
Must be "likely to require" work while energized
Must be in a "manhole, vault, or other enclosure designed for personnel access"
If they describe a pull box with just splices, this probably doesn't apply

4. Cross-References

Be ready to flip to 110.26 and identify what those requirements are (working space dimensions, lighting, headroom, dedicated space, etc.)
Know the basics of 110.34 for high-voltage (increased clearances, entrance/egress rules)

5. Trick Questions to Watch For

"Does this apply to equipment that's always de-energized?" (No – it must be "likely" to need work while hot)
"What if the manhole cover weighs 95 pounds?" (Not heavy enough – need 100 lbs minimum)
"Does this apply to outdoor substations?" (Read it carefully – it's for MANholes, VAULTs, and enclosed spaces for PERSONNEL ACCESS)

Bottom Line: Don't make underground electrical work a death trap. Give people room to work, light to see, and space to escape. If the space is tight enough that you wouldn't want to work in it with live parts, it's probably a violation. And remember: concrete holes in the ground follow the same electrical rules as rooms in buildings – physics doesn't care if you're underground.

Now quit making sardine cans with bus bars in them. Your future maintenance guy will thank you. 🔌⚡