Manufacturing Requirements for Electrical Distribution Box & Switch Box Enclosures

1. Material & Specifications

Distribution boxes and switch boxes shall be manufactured from cold-rolled steel sheet or flame-retardant insulating material

Steel Thickness:

Switch box enclosures: ≥ 1.2 mm

Distribution box enclosures: ≥ 1.5 mm

(General range: 1.2 mm to 2.0 mm)

The enclosure surface shall receive anti-corrosion treatment.

Enclosures shall be uniformly painted orange.

Wooden distribution boxes are prohibited.

2. Installation Requirements

Distribution boxes and switch boxes shall be installed upright and securely.

Mounting Height (Vertical distance from center point to ground):

Fixed type: 1.4 m to 1.6 m

Portable/Movable type: 0.8 m to 1.6 m

3. Enclosure Structure & Cable Entry/Exit

Cable entry and exit points shall be located on the bottom surface of the enclosure.

Entry/exit points shall be equipped with fixed cable clamps.

Incoming and outgoing cables shall be fitted with insulated bushings and securely clamped to the enclosure, preventing direct contact with the enclosure material.

Cables for portable/movable distribution boxes and switch boxes shall use rubber-sheathed insulated cables and must not have joints.

Plug-and-socket connectors are strictly prohibited for the power inlet of distribution boxes and switch boxes.

The enclosure structure shall protect against rain and dust (e.g., IP rating suitable for the location).

4. Internal Electrical Component Arrangement

(1) Component Requirements:

All electrical components within the box must be reliable and in good condition. Damaged or non-compliant components are strictly prohibited.

Upon delivery, electrical products must be verified for: Manufacturing License, Product Certificate of Compliance (CoC), Product Manual, and Factory Test Records.

(2) Installation Requirements:

Components (including sockets) shall first be mounted on a metal or non-wooden, flame-retardant insulating mounting plate.

This mounting plate shall then be securely fastened inside the enclosure.

Metal mounting plates shall be electrically bonded to metal enclosures.

Components (including sockets) shall be firmly secured to the mounting plate in their designated positions, without tilting or looseness.

The enclosure size shall be appropriate for the number and dimensions of the internal components. Mounting dimensions on the plate shall comply with relevant standards.

(3) Component Configuration by Box Type:

① Main Distribution Board (MDB):

Configuration depends on RCD (Residual Current Device) placement:

Configuration 1: Main Isolator Switch → Main RCD → Subcircuit Isolator Switch → Subcircuit Circuit Breaker (MCB/MCCB).

Configuration 2: Main Isolator Switch → Main Circuit Breaker (MCB/MCCB) → Subcircuit Isolator Switch → Subcircuit RCD.

Either configuration is acceptable.

The MDB shall also be equipped with: a Voltmeter, an Ammeter, a kWh Meter (Energy Meter), and other required instruments.

Installation of dedicated energy metering shall comply with local power utility regulations.

When Current Transformers (CTs) are installed, their secondary circuit must have a connection point to the Protective Earth (PE) conductor and must never be open-circuited (See Fig. 7-8).

② Sub-Distribution Board (SDB):

Components shall provide both control (isolation, normal switching ON/OFF) and protection (short-circuit, overload) functions.

Standard Configuration: Main Isolator Switch → Main Circuit Breaker (MCB/MCCB); Subcircuit Isolator Switch → Subcircuit Circuit Breaker (MCB/MCCB). (See Fig. 7-9).

③ Final Circuit Switch Box:

Mandatory Components: Isolator Switch, AND Circuit Breaker (MCB/MCCB) OR Fuse, AND RCD (Residual Current Device).

Exception: If the RCD incorporates short-circuit, overload, and earth leakage protection (RCBO), a separate Circuit Breaker or Fuse is not required.

The Isolator Switch must provide a visible isolation gap when open and disconnect all live poles. It shall be installed at the power inlet.

Exception: If the Circuit Breaker provides a visible isolation gap, a separate Isolator Switch is not required.