Wireman

A consumer unit is a particular type of distribution board that controls and distributes electrical energy, commonly in residential, domestic premises, building and factory circuit.

Consumer circuit for residential premise are installed for the following applications.

Lighting circuit for all lighting equipment.
Power circuit using switch socket outlet commonly known as Ring circuit.
Cooker circuit for kitchen area
Air-conditioning point
Water heater (thermostatic type) for shower bathroom.
Isolator point connects to any equipment/machinery application.
Radial Circuit for two socket outlet

1.2 Lighting circuit

Basically the lighting circuit is known as radial circuit.
The maximum number of point under one MCB shall be 10 point only.
Lighting circuit commonly uses miniature circuit breaker as protection against over-current be 6 A for general lighting.

1.3 Cable sizing for lighting circuit

There are two(2) type of circuit.

General lighting - for living area, bathroom, kitchen, bed room, dinning area. Cable conductor size for lighting circuit shall be 1.5mm² .
When using higher lighting equipment such as LP/HP discharge lamps - factory, building lamp rate 100 watt or greater. Conductor size at least 2.5mm² or greater .

1.4 Lighting category

There is two(2) category identified for lighting circuit.

non discharge lamp - this type of lighting bulb does not contain gases, example LED, filament bulb
dis-charge lamp - this type of lighting bulb have gases, example such as mercury, sodium, metal halite

Non-discharge lamp

Filament bulb
Incandescent
LED bulb
Halogen

Dis-charge lamp

Florescent
Sodium
Metal halite
High Intensity Discharge Lamp (HID)

1.5 Wiring Regulations for lighting installations

The following regulations regarding lighting circuits and types of lamps installed.

Minimal cable sizing for lighting circuit shall be 1.5mm.sq with total 10 lighting point under 6A MCB.
Lamp fitting with 2 or 3 lamp tubes shall apply cable on neutral with the cable sized shall be 2.5mm.sq.
Where lighting circuit can share with the common supply with any types of fans such as exhaust, ceiling mounted and wall mounted under the same MCB. However, if fans are more than 3 units then must be seperate MCBs.
All discharge lamps (mercury, sodium, metal halide) shall be using minimal size of 2.5 mm.sq ~ 4.0 mm.sq for circuit and protected under 10A or 16A MCB. Recommended wire up 4 numbers of lamp control by one(1) switch.

1.6 Protection for lighting circuit

All lighting circuit must be protected against over-current fault.
Type of protection commonly used is miniature circuit breaker rated 6A. Maximum power for lighting shall be 1000 watt to avoid fault.
Second type of protection is fuse or semi-enclosed fuse. However this type of protection is not recommend anymore in current practices. Local authority not allow anymore.

1.7 Lighting

All types of lighting equipment sold for public installation must acquired standard product quality.
More information on types of lighting equipment can be found, click here.

Power circuit

Common power circuit consist of the following.

ring circuit - floor area size shall 100m²
radial circuit - floor area size shall 75m²
spur circuit - additional socket point into the ring circuit
isolator point - single point for fixed equipment or machinery
air-conditioner point - single point for air-conditioner unit.
water heater for shower - single point only commonly installed inside bathroom
cooker point circuit - max number of point shall be switch socket outlet (13A) x 2no.

Cable size for power circuit

Standard type cable size for power circuit depending on the circuit installed. All conductor size must have copper inside at least 7 strands.

Ring circuit connected to standard switch socket outlet (S/S/O) shall be using 2.5mm².This circuit shall be protected by 32A MCB and the maximum number socket shall be 10 point.
Radial circuit connected to standard switch socket outlet (S/S/O) shall be using 2.5mm². This circuit shall be protected by 20 A MCB and the maximum number socket shall be 2 point only. Commonly use for cooker point circuit.

Spur circuit connected to standard switch socket outlet (S/S/O) shall be using 2.5mm². This circuit shall be protected by under same RING circuit 32 A MCB and the maximum number socket shall be 2 point only. Commonly use for add on to existing RING circuit.

Cable size for air-conditioning circuit

Air-conditioning point circuit (or AC point) connected to standard switch socket outlet (S/S/O) shall be using 2.5mm². This circuit shall be protected by 16 A MCB and the maximum number socket shall be 1 point only. Commonly use for air-conditioner rating below 3kW. Common type of socket shall be rated 15A round pin type.
If air-conditioner unit is rated 4 kW, the MCB shall be rated 20A and cable sized 4.0mm².
If air-conditioner unit is rated 5 ~ 6.5 kW or more, the MCB shall be rated 32A and cable sized 6.0mm².

Summary Table Consumer Circuit

Protection consumer circuit

Miniature circuit breaker

Rewirable fuse (Semi Enclosed Fuse)

Diagram Wiring

Lighting circuit

Lighting circuit are known as radial circuit and the following below are the common circuit for installations.

The common supply means applying the same phase line from first lighting switches then share this wire to other lighting switches through out the lighting circuit.

For three phase supply system it is important to connect each phase neutral conductor back to origin neutral terminal in distribution board.

For Reference

Figure showing a radial circuit.

a. 1way switch controlling single point

Refer to figure 1 is the typical 1way switch controlling 1 lamp point,

All cables must be protected by a PVC or G.I conduit system.
Standard cable size using 1.5mm.sq.
MCB rating shall be minimal 6 A.

Figure 1 For Reference only

b. 1way switch controlling three (3) point.

Refer to figure 2.

All cables must be protected by a PVC or G.I conduit system.
Standard cable size using 1.5mm.sq.
MCB rating shall be minimal 6 A.

Figure 2 For Reference only

c. 2 nos. of type 2way switch controlling single point.

This is commonly applied on staircase wiring. Two- way light switch consisting of three-terminal, the center of terminal are identified as common.

Refer to figure 3.

All cables must be protected by a PVC or G.I conduit system.
Standard cable size using 1.5mm.sq.
MCB rating shall be minimal 6 A.

2way switch terminal

L1 -- C -- L2

For Reference only

Figure 3

d. 2 nos. 2 way type of switch and an intermediate switch controlling single point.

This is commonly applied on staircase wiring.

Refer to figure 4.

All cables must be protected by a PVC or G.I conduit system.
Standard cable size using 1.5mm.sq.
MCB rating shall be minimal 6 A.

For Reference only

Figure 4

Power Circuit Diagram

Ring Circuit 8 point x switch socket outlet

Ring Circuit 8 point add with 2 point spur

Radial circuit

Formula Calculations on Consumer Circuit

Current Demand

All consumer circuit are connected and required to calculate each conditions.

Lighting Circuit Current demand

Basic formula for current demand (CD)

Formula 1 : Dis-charge lamp - sodium lamp, mercury, metal halite

CD = W x qty x 1.8 ÷ V

Formula 2 : None-discharge lamp - LED lamp, filament lamp, incandescent lamp

CD = W x qty ÷ V

A house installed the following lighting equipment

filament bulb 60W x 6nos

total current demand, CD = 60w x 6 ÷ 240v = 1.5 A

LED lamp 20w x 4nos

total current demand, CD =20w x 4 ÷ 240v = 0.33 A

halogen lamp 25w x 6nos

total current demand, CD = 25w x 6 ÷ 240v = 0.625 A

Total current demand is 1.5A + 0.33A + 0.625 A = 2.455 A

Note:

Refer to total current demand, the MCB shall use 6 A with cable sized 1.5mm² .

2. When calculating lighting loads of none discharge lamp types such as LED, filament, halogen, and incandescent

The following lighting are connected under a 6A MCB;

4nos x 40 watt filament lamp
5nos x 25 watt halogen lamp
6nos x 15 watt LED lamp

Find the total current drawn from the MCB ?

Solution:

4nos x 40w ÷ 240v = 0.66 ampere

5nos x 25w ÷ 240v = 0.52 ampere

6nos x 15w ÷ 240v = 0.375 ampere

Total current : 0.66 + 0.52 + 0.375 = 1.55 ampere

3. A house installed the following lighting equipment

sodium 150W x 3nos ;

total current demand, CD = 150w x 3 x 1.8 ÷ 240v = 3.375 A

mercury lamp 200w x 4nos ; -

total current demand, CD =200w x 4 x 1.8 ÷ 240v = 6 A

metal halite 175w x 5nos ;

total current demand, CD = 175w x 5 x 1.8 ÷ 240v = 6.56 A

Total current demand is ;

3.375 A + 6 A + 6.56 A = 15.935 A

Note:

Refer to total current demand, the MCB shall use 20 A with cable sized 2.5mm². Other option is to individually installed 6A MCB x1 and 10A MCB x2 at consumer unit.

4. Discharge lamp load calculations

The following lighting are connected under a 10 A MCB;

4nos x 200 watt mercury lamp
3nos x 175 watt sodium lamp - floodlight
6nos x 36 watt florescent lamp

Find the total current drawn from the MCB ?

Solution:

4nos x 200w x 1.8 ÷ 240v = 6.0 ampere

3nos x 175w x 1.8 ÷ 240v = 3.93 ampere

6nos x 36w x 1.8 ÷ 240v = 1.62 ampere

Total current : 6 + 3.93 + 1.62 = 11.55 ampere

Diversity Demand

Allowance or tolerance of each circuit according to condition installations.

For lighting circuit type premises:

househlod/residential 66%
shoplot, office, business premise 90%
hotel, motel, inn, hall, prayer area, apartment 75%