For information on the number of air switches (air openers) and the number of poles (P-number) in the distribution box of a 20′ expansion box, a comprehensive distribution system design and common industrial configurations, refer to the following information:
I. Number of openings
This kind of distribution box is usually configured with 6-10 circuits, the specific number should be combined with the actual demand for electricity:
1. main switch: 1 (mandatory)
2. partition control:
● Lighting circuit: at least 1
● Socket circuits: 2-4 circuits (ordinary sockets, independent circuits for high power equipment)
● Equipment-specific circuits: such as air conditioners, motors, etc. added as needed.
3. Extended reservation: some designs will reserve 1-2 spare circuits.
II. The number of open poles (P number)
Selected according to functional requirements:
1. Main switch: 2P or 4P air switch is required
● Double-pole (2P): cut off the fire wire and zero wire at the same time, applicable to single-phase power system
● Four-pole (4P): for three-phase electrical system (such as 380V industrial equipment), including zero wire control
2. Branch circuit:
● Lighting/ordinary sockets: mostly use 1P or 1P+N openers (only control the fire wire, zero wire through)
● High-power equipment (air conditioners, motors, etc.): give priority to 2P openers, to ensure complete disconnection
● Humid areas (such as outdoor equipment): need to be paired with a Leakage protector (2P leakage protection)
III. Configuration examples
| Circuit type | Number of openings | Polarity selection |
| Main switch | 1 | 2P |
| Lighting circuit | 1 | 1P |
| General outlet | 2 | 1P+N |
| Air conditioner/equipment only | 2 | 2P |
| Leakage protection circuit | 1 | 2P Leakage protection |
| Total | 7 pcs. | — |
⚠️ Actual configuration to be adjusted according to equipment power, voltage type (single phase/three phase) and safety codes. It is recommended to consult the technical drawings of the box or consult the manufacturer to confirm the specific parameters.
