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Planning The Electrical System

Planning The Electrical System. Safe means for the entrance of electrical supply into a building Means of disconnecting all electrical power in a building Means of limiting to a safe level the maximum amount of electrical current that can enter a building

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Planning The Electrical System

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  1. Planning The Electrical System • Safe means for the entrance of electrical supply into a building • Means of disconnecting all electrical power in a building • Means of limiting to a safe level the maximum amount of electrical current that can enter a building • Common point for grounding the electrical equipment • Safe means of subdividing the electrical supply to serve individual loads or group of loads

  2. Types of Service Entrance Panels • Circuit Breaker Type • Fuse Type

  3. Circuit Breaker Type Service Entrance Panel • When breaker trips, it may be reset after the problem has been corrected • Circuit breakers are easy to switch off • Circuit breakers are available in sizes to protect any circuit • Circuit breakers will take a short periods of overload without tripping • Circuit breakers cannot be tampered with • A larger size circuit breaker cannot be installed accidentally

  4. Fuse Type Service Entrance Panel • Cost less to purchase • Less convenient to use • When fuses “blows”, It must be replaced unless equipped with a special reset-type fuses

  5. Determining the size Service Entrance Switch • Size of dwelling • Appliances • Large Appliances (Ranges, Dryer, Water Heater, ect.) • 2 Small Appliance loads Circuits • Laundry Load Circuit • General Lighting load Circuit

  6. One Family Dwelling • 2000 square feet • Appliances • Range – 240 Volts • Dryer – 240 Volts • Water Heater –240 Volts • 2 Small Appliance Load Circuits – 120V • Laundry Load Circuits – 120V • General Lighting Load Circuit – 120V

  7. Computed Load for Dwelling • General Lighting load: • 2000 sq. ft. X 3 volt-Amperes = 6000VA • 6000VA divided by 120 Volts = 50 Amps

  8. Laundry Circuits • At least one laundry circuit is required by NEC • Must be 20 amp • The circuit may not serve any lighting outlets or outlets in any other room in the house • 3 circuits X 1,500 Watts = 4500 Watts • 4,500 Watts divide by 120 Volts = 37.5 A

  9. Major Appliances • Refrigerator 350 Watts • Freezer 350 Watts • Dryer 7,000 Watts • Dish Washer 700 Watts • Range/Oven 11,050 Watts • Water Heater 4,500 Watts Total 24,050 Watts Well Pump 2,000 Watts

  10. Heating and Cooling • 100% of the nameplate rating of Central Heating and Air Unit • 65% of the nameplate rating of central electric space heating, including supplemental heating elements • 65% of the name plate rating of electrical space heating if less than four separately controlled units • 40% of the nameplate ratings of electric space heating of four or more separately controlled units 9,600 Watt Central AC/Heat Pump

  11. Loads except Heating and Cooling • Small Appliance Load 4,500 Watts • General Purpose Load 6,000 Watts • Fixed Appliance Load 24,050 Watts • Other Items (Well Pump) 2,000 Watts Total Load 36,550 Watts

  12. Calculate Total Load • Heating/cooling Load @100% 9,000 Watts • First 10 KW of other Load @100% 10,000 Watts • Remainder of other Load @40% 10,620 Watts 36,500 – 10,000 = 26,550 Watts 26,550 X 40% = 10,620 Watts Total Load 30,220 Watts

  13. Total Amperage Requirement Total Load divided by 240 volts 30,220 Watts divided by 240 Volts = 125.9 Amps

  14. SERVICE ENTRANCE SWITCH SIZE Farm Shop

  15. Computing Farm Shop Load • 1200 sq. ft. Farm Shop • 1 - 240 Volt, 50 amp Welder 50 A • 1 – 230 Volt, 5 hp Air Compressor 28 A • 1 – 230 Volt, 2 hp Bench Grinder 12 A • 1 – 230 Volt, 3 hp Radial Arm Saw 17 A • 1 – 230 Volt, 3 hp Tilting Arbor Saw 17 A • 1 – 115 Volt, ¾ hp Drill Press (13.8) • 1 – 115 Volt, 1/3 hp Exhaust Fan (7.2) • 6 – Additional 120 Volt Outlet (6 X 1.5 A = 9 A) • 3 – Lighting Circuits with 15 outlets = 22.5 A

  16. Converting 115 Volt items to 240 Volts • Drill Press 13.8 Amps • Exhaust Fan 7.2 Amps • Additional Outlets 9.0 Amps • Lighting Outlet 22.5 Amps Total Amperage 52.5 Amps

  17. To Convert 115 Volts to 240 Volts • 52.5 Amps X120 Volts = 6300 VA • 6,300 VA divided by 240 Volts or ½ of 52.5 amps= 26.25 A

  18. Total Service Load • Welder 50 Amp • Air Compressor 28 Amp • Bench Grinder 12 Amp • Radial Arm Saw 17 amp • Tilting Arbor Saw 17 amp • Converted 115 Volt items 26.25 Amp Total Load 150.25 Amp

  19. Load without diversity • Loads most likely to operate at one time to produce the heaviest loads are: • Welder 50 Amps • Exhaust Fan 3.60 Amps • Half of Lighting 11.25 Amps Total 64.85 Amps Largest Motor is 5 hp; 28 amps X 125% = 35 Amps

  20. Computing Total Demand • Not less than the first 60 amps of all loads • 100% of largest demand load 64.85 Amps • 50% of the next 60 amps 30 Amps • 25% of remainder of other load 150.25 Amps – 124.85 Amps= 25.45 25% of 25.4 = 6.36 Amps Total Demand 101.21 Amps

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