1. Flush-Mount Junction Box Types (5 Common Sizes)
| Type | Back box size (mm) | Faceplate size | Application |
|---|---|---|---|
| 86-type | 75×75×50 | 86×86 | Switch / outlet |
| 146-type | 75×135×50 | 146×86 | Multi-gang switch |
| 120-type | 65×120×50 | 120×120 | Multi-function |
| Octagonal box | 80×80×50 | Octagonal faceplate | Lighting fixture |
| Deep back box | 75×75×60 | 86×86 | Extra depth / multiple wires |
2. 86-Type Flush-Mount Box (Most Common)
The 86-type is the most common flush-mount junction box in China,faceplate 86×86 mm, back box 75×75×50 mm. Suitable for single-gang switches, single-phase outlets, network cable faceplates and more. Available in PVC and steel plate: PVC for dry indoor areas, steel plate for locations requiring grounding.
3. 146-Type Flush-Mount Box (Multi-Gang Switches)
146-type = two 86-type boxes side by side, panel 146×86mm, back box 75×135×50mm. For two- and three-gang switches and multi-position socket combinations. When several switches need to sit together during fit-out, a 146-type box gives a cleaner result than two 86-type boxes.
4. Octagonal Box (for luminaires)
Octagonal boxes are used forceiling lights / pendant lightswiring and are installed inside the ceiling. The box body is octagonal, 80×80×50mm, with 2–4 knockouts. Available in steel and PVC; steel octagonal boxes must be connected to the PE conductor.
5. Key Points for Installing Flush-Mounted Boxes (3 Steps)
- Embedding: embed the box at the designed position during bricklaying or pouring, with the box opening flush to the wall surface, deviation ≤ 2mm.
- Pulling wire: after pulling conductors through the conduit, leave 150mm of slack inside the box and tag each conductor.
- Faceplate: install the faceplate after wall finishing is complete, tightening screws centered.
FAQ FAQ
What is the difference between 86-type and 146-type flush-mounted boxes?
An 86-type faceplate is 86×86mm for a single switch or socket; a 146-type faceplate is 146×86mm for two- or three-gang switches, equivalent to two 86-type boxes side by side.
Is PVC or steel better for flush-mounted boxes?
PVC is acceptable in dry indoor areas; where grounding is required (socket circuits), use a steel box and connect the PE conductor. Steel is recommended for public buildings.
Is there a depth requirement for flush-mounted boxes?
Standard depth is 50mm; use a 60mm deep back box when there are many conductors or a large cross-section. Too shallow and the conduit bend radius will be insufficient.
Where are octagonal boxes used?
Octagonal boxes are used forceiling luminaire wiring, installed inside the suspended ceiling or floor slab to connect the luminaire power conductors.
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