Chapter 4-1 Distribution Equipment up to 1kV

Chapter 4-1-1 Electric Equipment Installation

Article 305. Safety Installation of Electrical Equipment

When MCCB (Molded-Case Circuit-Breaker) is installed, it shall maintain the arc space*(safety boundary) between the power supply terminalof MCCB and obstacle such as metal wall and busbar,

according to manufacturer's instructions, in order to prevent the secondary fault as follows.

*Note : If the arc space is not enough, secondary fault may occur due to the conductivezedionigas which exhausted from the MCCB, during the breaking operation of the first fault at load side of MCCB.

(2)Then, a conductive ionized gas is exhausted from the power supply side

MCCB during the breaking operation.

(3)At this time, if an arc space (purple part) is not enough, a short circuit or an

(1) Firstly, a short-circuit fault occurs at the load side of MCCB

Arc Space (Not enough)

Insulated wire

Insulated Wire

Figure 305 The example of secondary fault due to the shortage of arc space

155

Article 306. Connection Method of Switching Devices

Switching devices have a fixed terminal and a movable terminal. Especially, -nonsealed switching devices such as a knife switch, have a movable terminal which can be touched easily. If the movable terminal is connected to the power supply side, in touchingthe exposed live part, an operator may get electric shock, although the switch is turned off. Therefore, the fixed terminal shall be connected to the power supply side, and the movable terminal shall be connected to the load side.

Power supply side

A movable terminal is exposed, and it is eas operators to touch theterminal, therefore, it shall b connected to the load side that can not be charged when the switch is turned off.

Load side

Figure 306 Connection diagram of knife switch

Article 307. Manually Controlled Switchgears

For fireproof performance of the protective case, the specification of the distribution panel board shall comply with the Article 315.

Article 308. Identification of Switching Devices

As stipulated in Technical Regulation

Article 309. Power Sources of the Automatic Circuit Breaker (Auto-breaker)

When a repair work, a removal/installation work, etc. of a circuit breakerare carried out, it shall get other isolation by the disconnector for safety work. But in the following cases, it is permissible not to get other isolation.

-Pull-out type circuit breakers

-In case that it can stop a wide range of equipment including the work object by opening the circuit

breaker on the upstream side.

- In case that it is ensured that the work of the auto-breaker can be carried out safely, although it is still energized at the both endsof it. (e.g.in case of the work which can keep the working clearance between live parts and the worker)

Article 310. Connecting Direction of Fuses

As for the installation of fuses, fuses shall be installed in such a way that their replacement can be carried out safely according to manufacturer's instructions.

156

In case of the following screw-in fuse, to prevent the electric shock in installing the fuse, the upper terminal of the fuse base shall be connected to the load side and the bottom terminal shall be connected to the power supply side.

Load side

Chapter 4-1-2 Distribution Panel Boards

Article 311. Minimum Clearance in Air of Bare Conductor

Air clearance between exposed live poles as well as between exposed live parts and non-live metal components shall be not less than 12mm. In the same case,creepage distance shall be not less than 20mm.

Air clearance between exposed conductors and protective barrier must be not less than: 100mm in case of wire mesh type and 40mm in case of insertable insulated walls.

Article 312. Site requirements for Electrical Cabinets

When the cable-laying of multilayer is performed, the permissible current of cable is reduced, due to the influence of mutual induction between cablesFor. this reason, the permissible current of the multilayer shall consider the following current reduction rate.

157

Table 312 Current reduction rate

Current reduction rate

Article 313. Conductor Material for Grounding Wire

Bare conductors are used for earthing conductors. So, due to mechanical strength and stability against corrosion minimum cross-sections of conductors are:

-Copper : 16mm2

-Aluminium : 35mm2

-Steel : 50mm2

Article 314. Controlling and Measurement Devices

The provisions of this article shall refer to the chapter 2 -6 and 5-3.

Article 315. Flame-resistant Materials for the Distribution Panel Boards

(Reference) Japanese specification of distribution boards with heat-resistant

The distribution board which supplies a power to the disaster prevention equipment, such as an indoor fire hydrant, a sprinkler, a smoke ventilation and an emergency outlet, etc. shall have the following heat-resistant specification.

-The distribution board which installed in the place with the potentiality of the fire spread, such as

a living room, a roof terrace, general passage way, general staircase and outdoor, shall be the

first-class heat-resistant.

- The distribution board which installs in the place without the potentiality of the fire spread, should be the second-class heat-resistant.

158