Wireways versus Auxiliary Gutters
Wireways vs. Auxiliary Gutters: A Technical Comparison Under the 2023 NEC
By Electrical Code Academy, Inc.
Wireways Defined
A wireway is a raceway constructed with a rectangular cross-section and removable or hinged covers along its length. The design permits accessible routing, pulling, splicing, and tapping of conductors within the enclosure.
- Conductor fill: At any cross-section, total conductor area ≤ 20% of the interior cross-sectional area.
- Ampacity adjustment:
- Metallic wireways: Apply adjustment factors only when >30 current-carrying conductors (CCC) are present at a cross-section.
- Nonmetallic wireways: Apply adjustment factors when >3 CCC are present (the general rule).
- Length: No NEC-imposed maximum length; compliance hinges on fill, ampacity adjustment, support, and listing.
Auxiliary Gutters Defined
An auxiliary gutter is a supplemental wiring space installed adjacent to equipment (e.g., panelboards, switchboards, MCCs). It is not a general-purpose raceway; it relieves congestion at terminations and provides space for conductor bends, taps, and splices.
- Length: Total length limited to 30 ft (applies to metallic and nonmetallic auxiliary gutters).
- Conductor fill: At any cross-section, total conductor area ≤ 20% of the interior cross-sectional area.
- Ampacity adjustment:
- Metallic auxiliary gutters: Apply adjustment factors only when >30 CCC are present at a cross-section.
- Nonmetallic auxiliary gutters: Apply adjustment factors when >3 CCC are present.
Splices, Taps, and Terminations — Required Practices
Both wireways and auxiliary gutters allow splices and taps. The following limits and good-practice items are critical for compliance and performance:
- 75% occupancy at the splice/tap location: At the exact cross-section where splicing/tapping hardware is installed, the combined area of conductors plus splice/tap devices must not exceed 75% of that cross-section.
- 20% conductor fill still applies: Away from splice/tap points, the conductor-only fill cannot exceed 20% at any cross-section.
- Accessibility: Splices/taps must remain accessible by the removable/hinged covers. Do not bury or obstruct access with other equipment or building finishes.
- Listed devices only: Use splicing/tapping means listed and identified for the conductor type, size, and environment (temperature rating, insulation type, and enclosure rating).
- Bend radius and mechanical strain: Provide adequate bending space and strain relief; avoid sharp edges and ensure raceway/entry fittings are listed and properly installed.
- Bonding and continuity: Maintain effective bonding and equipment grounding continuity across all enclosures and fittings; install bonding jumpers where required.
- Conductor organization: Arrange, secure, and label conductors to minimize heat buildup, facilitate inspection, and maintain clear cover closure.
Comparative Analysis
| Feature | Wireway | Auxiliary Gutter |
|---|---|---|
| Primary function | Raceway for routing conductors with accessible covers for pulls, splices, and taps. | Supplemental wiring space directly adjacent to equipment for bends, splices, and taps. |
| Length limitation | No NEC maximum. | 30 ft maximum (metallic and nonmetallic). |
| Conductor fill | ≤ 20% at any cross-section. | ≤ 20% at any cross-section. |
| Splice/tap occupancy (local cross-section) | ≤ 75% (conductors + devices) at splice/tap point; 20% conductor-fill still governs elsewhere. | ≤ 75% (conductors + devices) at splice/tap point; 20% conductor-fill still governs elsewhere. |
| Ampacity adjustment trigger | Metallic: >30 CCC Nonmetallic: >3 CCC | Metallic: >30 CCC Nonmetallic: >3 CCC |
| Typical deployment | Extended horizontal/vertical routing across rooms or equipment lineups. | Short enclosure mounted to the side/top of equipment to relieve termination congestion. |
Code Application Significance
Common violations include: using an auxiliary gutter like a long raceway, exceeding 20% conductor fill, overlooking the 75% splice/tap occupancy at the local cross-section, or misapplying ampacity adjustment triggers—especially on nonmetallic products. Each error increases the risk of excessive heating, poor serviceability, and failed inspections.
Advance Your NEC Knowledge
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