E4 Electrical Installation

#1 Power Distribution

© 2005 Refrigeration Training Services - E4#1 Power Distribution, Delta & Wye Systems v1.2 2

Electrical Distribution

200,000 – 400,000 Volts

SubstationTransformers Drop Voltage To 7200 Volts

7200 Volts

7200 Volts

208/480 VoltsThree Phase (3Ø)

120/240 VoltsSingle Phase (1Ø)

TransformerDrops VoltageTransformer

Drops Voltage

© 2005 Refrigeration Training Services - E4#1 Power Distribution, Delta & Wye Systems v1.2 3

Power at the Pole

• A step-down transformer mounted to a pole can provide normal voltage directly to a building close to the pole

• When the building is far from the pole, the high voltage is run underground to a transformer near the building

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Line Voltage 7200 Volts

Ground

Fuse

7200 Volts underground to transformer at House #2

7200v Primary

120/240v underground to electric panel in

House #1

Tap for 7200v

1 Pole, 2 Houses, 2 Transformer Types

120/240v Secondary out of transformer

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Transformers

• Following is a picture of an underground service transformer– The transformer is stepping down 7200 volts

to 120/240 volts– Take note of the safety precautions practiced

by the power company technician

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Underground Service

Transformer

Transformer 7200v Primary

120/240v Secondary

Rubber Arm

Shields

Thick Rubber Gloves

Eye Protection

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Electric Meter

• Meter hub on a residence

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Electric Meter

Meter Enclosure

Power In

Power out to electric panel

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Residential Single Phase Power

• Following is a diagram of 120/240 volt 1Ø power

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L1 L2 N

240v

120v

120v

Common Residential 120/240v-1Ø

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Electric Panel

• Inside the building is the electric panel• Circuit breakers distribute the power

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Good Workmanship

Counts

Smooth bends in the wires

Typical 1Ø Electric Panel

Cable ties

Main Breaker

Neutral

Ground

Circuit Breakers

Bus Bars

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