Planning The Electrical System

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

May 2007
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 12 kilowatts
• Dryer 240 Volts 5.5 kW
• Water Heater 240 Volts 5 kW
• 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 1,150 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 _at_100 9,000 Watts
• First 10 KW of other Load _at_100 10,000 Watts
• Remainder of other Load _at_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