Separate Structure Disconnecting Means Calculator
When a feeder or branch circuit leaves one building and lands in a detached garage, shop, barn, or shed, the National Electrical Code (NEC) 225.31 through 225.33 governs the disconnecting means at that separate structure. Enter the supply, how many disconnects you have, and where they are, and this tool checks whether a disconnect is required, whether its location meets 225.32, and whether the count is within the 225.33 maximum of six.
How to use this calculator
- Pick what supplies the separate structure: a feeder (the usual subpanel case), a single branch circuit (a multiwire branch circuit counts as one), or more than one branch circuit.
- Enter how many switches or circuit breakers make up the disconnecting means for that supply.
- Choose where the disconnect is: nearest the point of entrance, or elsewhere on the premises.
- If it is elsewhere, pick the 225.32 exception that permits it; set whether it is readily accessible.
- Read the result: whether a disconnect is required (225.31), whether the location passes (225.32), whether the count passes (225.33), and an overall compliance verdict.
NEC reference
This calculator implements NEC 2020 Article 225, Part II, for buildings or structures supplied by a feeder or branch circuit. Section 225.31 requires a means to disconnect all ungrounded conductors that supply or pass through the structure. Section 225.32 requires that disconnecting means to be inside or outside the structure served, or where the conductors pass through it, at a readily accessible location nearest the point of entrance, with four exceptions permitting it elsewhere on the premises. Section 225.33 limits the disconnecting means for each supply to not more than six switches or six circuit breakers. NEC 2020 is the site default; these sections are substantially unchanged across the 2017, 2020, and 2023 editions.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
The three questions 225.31-225.33 answer
Feeding a detached garage, shop, barn, or well house from a service in another building raises the same three questions every time. Article 225, Part II answers each one.
| Question | Rule | Source |
|---|---|---|
| Is a disconnect required? | Yes - a means to disconnect all ungrounded conductors that supply or pass through the structure | 225.31 |
| Where does it go? | Readily accessible, nearest the point of entrance (inside or outside), unless a 225.32 exception permits elsewhere | 225.32 |
| How many are allowed? | Not more than six switches or six circuit breakers per supply; a single enclosure is still permitted | 225.33 |
Why 225.33 is not the service rule
The most common mistake here is carrying the 2020 service-disconnect change into Article 225. The 2020 NEC revised 230.71 so that the two to six disconnecting means for a service can no longer be grouped in a single panelboard; each must sit in its own separate enclosure, vertical section, or compartment. That change applies to services only. Article 225.33, which governs feeders and branch circuits to a separate building or structure, was not changed. It still lets the two to six disconnects share a single enclosure, sit in a group of separate enclosures, or live on a switchboard or in switchgear, so six breakers in one main-lug panel at a detached garage remains compliant under 225.33. This tool applies no separate-enclosure requirement to a 225.33 count.
The 225.32 location exceptions, in full
The default rule is simple: the disconnect goes at a readily accessible point nearest where the supply conductors enter the structure, inside or outside. Four exceptions let it live elsewhere on the premises, and all four are narrow:
- Exception No. 1 - single management. Installations under single management with documented, established, and maintained safe switching procedures, monitored by qualified individuals.
- Exception No. 2 - Article 685. Buildings or structures qualifying as integrated electrical systems under Article 685.
- Exception No. 3 - lighting standards. Towers or poles used as lighting standards.
- Exception No. 4 - sign poles. Poles or structures used only to support signs installed per Article 600.
An exception only relaxes the “nearest the point of entrance” requirement. The disconnecting means must still be readily accessible wherever it is placed.
Worked examples
A feeder runs to a 100 A subpanel in a detached garage, and the panel has a single main breaker mounted just inside the wall where the feeder enters. A disconnect is required (225.31), it is readily accessible nearest the point of entrance (225.32), and one disconnect is well within the maximum of six (225.33). The installation complies.
A barn is fed by one feeder that lands in a main-lug panel with six branch breakers used as the disconnecting means, all in one enclosure just inside the entrance. Six is the maximum under 225.33(A), and because this is Article 225 rather than a service, the single enclosure is permitted. It complies. Add a seventh disconnect and the count fails 225.33.
A pole-mounted lighting standard on the property has its feeder disconnect at a panel 80 feet away rather than at the pole. Because the structure is a lighting standard, 225.32 Exception No. 3 permits the disconnect elsewhere on the premises, so long as it stays readily accessible. It complies.
Common mistakes
- Applying the service separate-enclosure rule. 230.71's 2020 change is for services; 225.33 still allows six feeder disconnects in one enclosure.
- Skipping the disconnect entirely. A feeder or branch circuit to any building or structure needs a disconnecting means (225.31), even a small shed.
- Burying the disconnect out of reach. It must be readily accessible, not behind stored material, above a ladder-only height, or in a locked space the occupant cannot reach.
- Placing it deep inside the building. Without a 225.32 exception, the disconnect must be nearest the point where the conductors enter, not at the far end of a long run inside.
- Confusing the disconnect rule with grounding. 225.31-225.33 is the disconnect; the ground rod, EGC, and neutral treatment at the structure are 250.32.
Frequently asked questions
Does a detached garage need its own disconnect?
Yes. 225.31 requires a means to disconnect all ungrounded conductors supplying any building or structure, so a feeder-fed garage subpanel needs a disconnect that also meets the 225.32 location rule.
Where does the disconnect go?
At a readily accessible location nearest the point of entrance of the supply conductors, inside or outside the structure (225.32), unless one of the four exceptions permits it elsewhere on the premises.
How many disconnects can I have?
Up to six switches or six circuit breakers per supply (225.33(A)). Unlike the service rule, they may be in a single enclosure, separate enclosures, or a switchboard or switchgear.
What about grounding the detached building?
That is a separate question under 250.32: the grounding electrode, the equipment grounding conductor, and isolating the neutral. Use the Separate Structure Grounding Calculator.
Related calculators
- Separate Structure Grounding & Bonding Calculator: the grounding half of the same question per NEC 250.32 - electrode, EGC, and neutral treatment.
- Service Disconnect Number & Rating Calculator: the parallel rule for a service per NEC 230.71/230.79, including the 2020 separate-enclosure change.
- Equipment Grounding Conductor Size Calculator: size the EGC run with the feeder to the structure per NEC Table 250.122.
- Emergency Disconnect Requirement Calculator: the NEC 230.85 emergency disconnect for one- and two-family dwellings.
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