EE4503 Electrical Systems Design

1. EE4503Electrical Systems Design Branch circuit and Feeder (Lighting and Appliances)

2. Topics • Characteristics of Loads • Circuits Design • Branch Circuit • Feeder Circuit • Load Schedule

3. Characteristics of Loads • Continuous Load • More than 3 hrs. of continuous usage e.g. lighting, air condition • Non-continuous Load: • Less than 3 hrs. of continuous usage e.g. electric oven, microwave When not sure, add 25% more

4. Characteristics of LoadsDefinition • Total Connected Load: total kVA or MVA listed • Maximum Demand: the maximum kVA or MVA used at the same time

5. Characteristics of LoadsDefinition • Demand Factor (D.F.): ratio of “Maximum Demand” to “Total Connected Load” () • Diversity Factor: summation of every branched circuits’ maximum demand to the system’s maximum demand (always greater than or equal to 1.0)

6. Characteristics of LoadsDefinition • Peak Load (P): the maximum kVA or MVA at the given periond (e.g. 15 min) • Load Factor (L.F.): ratio of “Average Load” to the “Peak Load” (). is total energy for period of time

7. Characteristics of LoadsCommon Load • Lighting: about 20-50% of total load or 20-100VA/m2 • Receptacle: if no specific information, 180-200VA/set (1, 2 or 3 outlets) • HVAC: 1TR (12,000 BTU) is about 1.5-1.8kVA • Motor • Escalator: manufacturer’s specification

8. GroundingCommon Load - Lighting http://www.g-w.com/pdf/sampchap/9781605255880_ch12.pdf

9. GroundingCommon Load - Escalator http://www.elevatorbooks.com/Content/Site108/ProductContent/April2012Articl_00000012203.pdf

10. Circuit Design • Branch Circuit • Feeder Circuit • Main Circuit

11. Branch Circuit • Connect from a distribution panel to load or receptacle • Lighting or Appliance Branch Circuit • Lighting Branch Circuit • Receptacle Branch Circuit • Lighting & Receptacle Branch Circuit • Individual Branch Circuit

12. Branch CircuitCalculation • Load of a branch circuit (BC) at least the total load connected to that branch. • Conductor Sizing  Current Rating of CB • Current Rating of CB Maximum Load • Size of a BC goes by the current rating of CB: 15(16)A, 20A, 25A, 30(32)A, 40A, 50A, 63A

13. Branch CircuitDesign Procedure • Find “Load” • Calculate “Circuit Breaker” (% of BC) • Calculate “Cable” • Verify “Voltage Drop”: 1-2% of rated voltage ?? safety factor ??

14. Branch CircuitDesign Recommendations • Lighting Circuit: continuous load • 50-70% of BC (no more than 80%) or allowance of 10-30% • Individual Branch Circuit: load is known • Should be no more than 80% of BC

15. Branch CircuitDesign Recommendations • Receptacles Circuit: single, duplex, triplex • 180VA per set (200VA for ease) • Individual Circuit with ELCB: heater, Jacuzzi • Receptacles Circuit with ELCB: toilet, kitchen, basement, outdoor, < 1.5m from water ?? Some recommendations can be relaxed ??

16. Branch CircuitDesign Recommendations • Separate the type of load: lighting on one BC • Future Load: • 20% spare at least • 40% if continuous load • Cable size is no smaller than 2.5mm2 • BC for receptacles contains less than 10 sets

17. Branch CircuitDrawing • # of hash marks is # of cables • No hash mark means 2 cables • One hash mark + number is the number of cables • Arrow + Lx is connected to circuit breaker (phase) #x

18. Branch CircuitPanelboard • No more than 42 circuit • No longer than 50 m • Easy to access (no higher than 1.8m) • Rated is more than the rated of the cable • At least one panel board per floor • Must have protection equipment (CB)

19. Branch CircuitPanelboard • Should be in the center: balance the voltage drop • Should be close to the incoming: shortest feeder • Three types • Active Branch Circuit (60-80%) • Spare Branch Circuit with CB (10-20%) • Spare Branch Circuit (10-20%)

20. Branch CircuitFeeder • Rated current of feeder is the total load deducted by the “demand factor” • Feeder Cable  Rating of CB • Rating of CB Feeder’s Rated Current

21. Branch CircuitFeeder – Demand Factor • Demand Factor is the ratio of the maximum usage power at any certain time to the total connected load. • There are tables for the demand factor, e.g. receptacles in kitchen, lighting. If not specify, 0.8 is a good number

22. Branch CircuitFeeder – Neutral • In single phase system, neutral cable will be the same size and line cable. • In three phase, neutral cable can be reduced. • Less than 200A, use the phase current • More than 300A • Without Harmonics, • With Harmonics, use the phase current

23. Branch CircuitFeeder - Design Procedure • Sum up total BCs’ load • Calculate “Circuit Breaker” • Calculate “Cable”: Phase then Neutral • Verify “Voltage Drop”: 1-2% of rated voltage

24. Branch CircuitLoad Schedule • List of connected load • CB number start from 1(A), 3(B), 5(C), 2(A), 4(B), 6(C) then 7(A), 9(B), 11(C), 8(A), 10(B), 12(C) • Consider the balance of load in all phases (less than 20% is recommended)

25. Branch CircuitLoad Schedule – Design Recommendation • Load Calculation • Non-continuous Load, no multiplier • Continuous Load, 1.25 multiplier (or more in case of future expansion) • If not sure, treat as continuous load. • Then choose the circuit breaker • Then choose the cable

26. Branch Circuit & FeederDesign Procedure • Make the Load Schedule • Design Branch Circuit • Design Feeder (from the load schedule)

27. Branch Circuit & FeederDesign Examples

28. Branch Circuit & FeederDesign Examples

29. Reference • Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์