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NEC 225.31: Disconnecting Means for Buildings and Structures

NEC 225.31: Disconnecting Means for Buildings and Structures

NEC 225.31: Disconnecting Means for Buildings and Structures

When power is supplied to a building or structure from another source, the ability to quickly and safely disconnect that power becomes critical. NEC 225.31 establishes the core rule that governs this requirement, and it’s one of the most frequently enforced sections on commercial and industrial inspections.

If you’re working on exterior feeders, detached structures, site utilities, or multi-building facilities, NEC 225.31 is non-negotiable.

👉 If you’re new to the Code or want the big picture first, start with our NEC Overview: What It Is and Why It Matters.
👉 For distribution fundamentals, review NEC Services and Feeders Explained before diving into this article.

 

 

What NEC 225.31 Requires

NEC 225.31 states:

“Means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.”

In plain language:

  • Every building or structure supplied by feeders or branch circuits must have a disconnecting means.

  • That disconnect must shut off all ungrounded (hot) conductors supplying that structure.

This applies whether power is coming from:

  • A utility service

  • Another building

  • A generator or alternate source

 

 

When NEC 225 Applies (and When It Doesn’t)

NEC 225 Applies To:

  • Detached buildings supplied from another structure

  • Site-fed equipment buildings

  • Parking structures

  • Accessory buildings (commercial & industrial)

  • Pole-mounted or pad-mounted structures

NEC 225 Does Not Apply To:

  • Buildings supplied by service conductors (Article 230 applies instead)

  • Structures considered part of the same building (per AHJ interpretation)

This distinction is why NEC 225.31 is often confused with service disconnect rules.

 

 

Location Requirements (NEC 225.32)

While 225.31 establishes that a disconnect is required, NEC 225.32 tells you where it must be located:

  • Readily accessible

  • Outside the building or

  • Inside nearest the point of entry

Inspectors are extremely strict here. A disconnect buried deep inside a building almost always gets flagged.

This ties directly into how feeders are routed and sized under NEC 215.2: Minimum Rating and Size of Feeder Conductors.

 

 

How NEC 225.31 Ties Into Services and Feeders

NEC 225 is essentially the bridge between services and feeders:

  • Article 230 → utility service disconnect rules

  • Article 215 → feeder sizing and protection

  • Article 225 → building-level disconnecting means for feeders

If you’re supplying a building with feeders (not service conductors), NEC 225.31 becomes your governing rule.

For a refresher on how feeders are defined and protected, see Services and Feeders Explained.

 

 

Ground-Fault & Load Considerations

Large feeders supplying detached buildings often trigger additional requirements:

  • Ground-Fault Protection → see NEC 215.10: Ground-Fault Protection of Feeders

  • Existing Load Evaluations → see NEC 220.87: Determining Existing Loads

  • Lighting Load Demand Factors → see NEC 220.42

NEC 225.31 doesn’t exist in isolation — inspectors expect the entire system to work together.

 

 

Common Contractor Mistakes

❌ Assuming a panel inside the building counts as the disconnect
❌ Placing the disconnect too far from the point of entry
❌ Forgetting to disconnect all ungrounded conductors
❌ Poor or missing labeling on the disconnect
❌ Confusing service disconnect rules with feeder disconnect rules

These are some of the most common red-tag issues on commercial inspections.

 

 

Labeling Requirements (Often Overlooked)

While NEC 225.31 establishes the disconnect requirement, NEC 110.22 requires that disconnecting means be clearly and durably marked.

This includes:

  • Identifying what building or structure is supplied

  • Indicating the source of power

  • Ensuring emergency personnel can locate the correct disconnect

✅ At Print Pro, we supply NEC-compliant disconnect labels and placards specifically designed for feeder-supplied buildings and structures — helping contractors pass inspections without delays.

 

 

Pro Tips for Contractors

  • Always determine early whether you’re dealing with service conductors or feeders — this decides whether Article 230 or 225 applies.

  • Place disconnects outside or immediately inside the structure — don’t gamble on inspector interpretation.

  • Coordinate feeder sizing (NEC 215.2) and disconnect ratings together.

  • Label disconnects during rough-in — inspectors appreciate clarity.

  • When in doubt, confirm with the AHJ before installation.

 

 

Conclusion

NEC 225.31 ensures that buildings and structures supplied by feeders can be safely and quickly disconnected in emergencies, maintenance, or fault conditions. For contractors, compliance is about more than installing a switch — it’s about location, coordination, and clear identification.

To understand how this fits into the broader NEC framework, review:

👉 Need inspection-ready disconnect and feeder labels? Visit PrintProAZ.com to get NEC-compliant solutions trusted by contractors nationwide.

 

 



Tags:
NEC 220.87: Determining Existing Loads for Calculating Service and Feeder Sizing
NEC 230.71: Service Disconnecting Means — The “Six Disconnect Rule” Explained