17 | Current Demand and Diversity

17

Current Demand and Diversity

What is current demand ?

Current Demand Table (IEE)

Household example calculations:

What is diversity demand

Allowance for diversity Table

Household example calculations:

Allowance for diversity Table

Example calculations for office

Allowance for diversity Table C

Example calculations for hotel

What is current demand ?

Current Demand or Maximum demand is the maximum anticipated installation load plus any allowance for future loading. Maximum demand (often referred to as MD) is the largest current normally carried by circuits, switches and protective devices.

CD does not include the levels of current flowing under overload or short circuit conditions. When assessing maximum demand, account must be taken of the possible growth in demand during the life of the installation.

Current Demand Table (IEE)

Type of outlet

2 A socket outlet
Other socket outlets
Lighting point
Shaver outlet, bell transformer<5W
Household cooker

Assumed current demand

At least 0.5A
Rated current (I = P ÷ V)
Connected load, with minimum of 100 W
May be neglected (Ignored)
10A + 30% of remainder + 5A for socket in cooker unit

Household example calculations:

1. Lighting Circuit

- 5nos. of 36 watt Florescent Lamp = 36w x 5 x 1.8 ÷ 240v = 1.35 A

- 3nos. of 18 watt Florescent Lamp = 18w x 3 x 1.8 ÷ 240v = 0.40 A

-1no. of 80 watt Ceiling Fan = 80w x 1.8 ÷ 240v = 0.6 A

- 2nos. of 50 watt wall fans = 50w x 2 x 1.8 ÷ 240v = 0.75 A

Note: Wx1.8 for inductive load (or discharge lamps) with switch gear and ballast factor included.

Total Current Demand for lighting is; 1.35 + 0.4 + 0.6 + 0.75 = 3.1 A

2. Power socket outlet (For ringed circuit)

- 1no. 1800 watt Washing machine = 1800w ÷ 240v = 7.5 A

- 1no. 600 watt refrigerators = 600w ÷ 240v = 2.5 A

- 1no. 300 watt TV = 300w ÷ 240v = 1.25 A

- 1no. 500 watt Computer = 500w ÷ 240v = 2.08 A

Total Current Demand for power point is; = 7.5 + 2.5 + 1.25 + 2.08 = 13.33 A

3. Cooker Point (known as radial circuit)

- Electric oven 2500 watt and electric rice cooker 380 watt

Solution: Ib = (2500w + 380w) ÷ 240v = 12 A

CD = 10A + 5A + (Ib - 10) x 0.3 (0.3=> 30% remainder)

= 15A + (12A-10A) x 0.3 = 15.6 A

4. Water Heater (for Shower)

Consider as 100% as maximum load. Example a water heater 1500 watt/240v.

current demand CD = P ÷ V = 1500w ÷ 240v = 6.25 A

Total current demand from all calculation above (1,2,3,4) is ;

= 3.1 A + 13.33 A + 15.6 A + 6.25 A = 38.28 A

What is diversity demand

Diversity demand is the ratio of maximum demand to the connected load.

Sometime this also known as "estimated current".

Formula;

Diversity = maximum demand ÷ connected load

There three(3) areas for this diversity factor table:

residential or house hold
commercial - shoplot, offices
commercial - guest house, hotel, hall

Allowance for diversity Table

House hold or Residential

Type of circuit :

Lighting
Heating and power
Cookers Point (for Kitchen)
Instantaneous water heaters
Thermostatic water heaters
Standard circuits
Sockets and stationary eqt
Electric motor

Household

66% of CD
100% up to 10 A + 50% balance
10 A + 30% balance + 5 A for socket
100%X + 100%Y + 25%Z
100% of CD
100%X + 40%(Y+Z)
100%X + 40%(Y+Z)
100% of CD

Note the following abbreviations :X is the full load current of the largest appliance or circuitY is the full load current of the second largest circuitZ is the full load current of the remaining appliances or circuits

Household example calculations:

1. Lighting circuit

Given the total lighting current demand is 3.25 A, find the diversity load?

DL = CD x 66% = 3.25A x 66÷100 = 2.145 A

2. Power circuit (ringed circuit)

- 1no x 1300 watt Hifi system CD= P ÷ V = 1300w ÷ 240v = 5.416 A (marked Y second largest current in circuit)

- 1no x 1500 watt washing machine CD= P ÷ V = 1500w ÷ 240v = 6.25 A (marked X largest current in circuit)

- 1no x 350 watt TV CD= P ÷ V = 350w ÷ 240v = 1.45 A (marked z remainder current in circuit)

- 1no x 560 watt Desktop computer CD= P ÷ V = 560w ÷ 240v = 2.33 A (marked z remainder current in circuit)

Total diversity is DL = X + (Y + Z) x 40%

= 6.25 A + ( 5.416 A + 1.45A + 2.33A ) x 0.4 = 9.92 A

3. Cooker Point

- Electric cooker pot 2500 watt and electric rice cooker 320 watt

Solution: Ib = (2500w + 320w) ÷ 240v = 11.75 A

CD = 10A + 5A + (Ib - 10) x 0.3 (0.3=> 30% remainder)

= 15A + (11.75 A-10 A) x 0.3 = 15.52 A

Total diversity from all calculation (1,2,3) above is ; = 2.145 A + 9.92 A + 15.52 A = 27.585 A

Allowance for diversity Table

Offices, Shop Unit

Type of circuit :

Lighting
Heating and power
Cookers Point (for Kitchen)
Instantaneous water heaters
Thermostatic water heaters
Standard circuits
Sockets and stationary equipment
Electric motors (but not lifts)

Shop lot unit, Office

90% of CD
100%X + 75%(Y+Z )
100%X + 80%Y + 60%Z
100%X + 100%Y + 25%Z
100% of CD
100%X + 50%(Y+Z)
100%X + 75%(Y+Z)
100%X + 80%Y + 60%Z

Example calculations for office

1. Lighting circuit

Given the total lighting current demand is 16.5 A, find the diversity load?

DL = CD x 90% = 16.5A x 90 ÷100 = 14.85 A

2. Power circuit (ringed circuit)

- 1no x 1300 watt Hifi system CD= P ÷ V = 1300w ÷ 240v = 5.416 A (marked z second largest current in circuit)

- 1no x 860 watt Fridge CD= P ÷ V = 860 w ÷ 240v = 3.58 A (marked z largest current in circuit)

- 1no x 380 watt TV CD= P ÷ V = 380w ÷ 240v = 1.45 A (marked z remainder current in circuit)

- 4nos. x 560 watt Desktop computer CD= P ÷ V = (4 x 560w) ÷ 240v = 9.33 A (marked Y remainder current in circuit)

- 1no. x 2500 watt photostat machine CD= P ÷ V = 2500w ÷ 240v = 10.41 A (marked X remainder current in circuit)

Total diversity is DL = 100%X + 75%(Y+Z)

= 10.41 A + ( 9.33A + 5.416 A + 3.58 A + 1.45A ) x 0.75 = 25.24 A

3. Thermostatic water heaters ( diversity current no allowance, 100% of CD )

Electric water heater 2900 watt CD= P ÷ V = 2900 w ÷ 240v = 12.08 A

Total diversity from all calculation (1,2,3) above is ; = 14.85 A + 25.24 A + 12.08 A = 52.17 A

Allowance for diversity Table C

Hotels, guest houses, Hall

Type of circuit :

Lighting
Heating and power
Cookers Point (for Kitchen)
Instantaneous water heaters
Thermostatic water heaters
Standard circuits
Sockets and stationary equipment
Electric motors (but not lifts)

Hotels, guest houses

75% of CD
100%X + 80%Y + 60%Z
100%X + 80%Y + 60%Z
100%X + 100%Y + 25%Z
100% of CD
100%X + 50%(Y+Z)
100%X + 75%Y + 40%Z
100%X + 50%(Y+Z )

Example calculations for hotel

1. Lighting circuit

- 3nos. x 60 watt incandescent lamp CD = 3 x 60 w ÷ 240 v = 0.75 A

- 4nos. x 11 watt LED lamp CD = 4 x 11 w ÷ 240 v = 0.18 A

- 2nos. x 50 watt halogen lamp CD = 2 x 50w ÷ 240 v = 0.41 A

Note: All lamps above are non-discharge lamps, therefore x1.8 shall not applied.

Total current demand , CD is ; 0.75A + 0.18A + 0.41A = 1.34 A

Diversity factor is ; DL = CD x 75% = 1.34 A x 0.75 = 1.0 A

2. Power circuit (ringed circuit)

- 2nos. x 50 watt table lamp CD= P ÷ V = 2 x 50 w ÷ 240v = 0.41 A (marked z largest current in circuit)

- 1no x 460 watt small Fridge CD= P ÷ V = 460 w ÷ 240v = 1.91 A (marked Y largest current in circuit)

- 1no x 520 watt TV CD= P ÷ V = 520w ÷ 240v = 2.16 A (marked X remainder current in circuit)

- 1no. x 430 watt hair dryer CD= P ÷ V = 430 w ÷ 240v = 1.79 A (marked z remainder current in circuit)

Total current demand , CD is ; 0.41 A + 1.91 A + 2.16 A + 1.79 A = 6.27 A

Diversity factor is ; DL = 100%X + 50%(Y+Z)

= 2.16 A + (1.91 A + 1.79 A + 0.41 A) x 0.5 = 4.215 A

Total diversity from all calculation (1,2) above is ; = 1.0 A + 4.21 A = 5.21 A