Unit 7 - Electrical Systems

Confidence Level

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BASIC DEFINITIONS

┌──────────────────────────────┐
│         VOLTAGE (V)          │
│    (Electrical force)        │
│    pushes electricity        │
└─────────────┬────────────────┘
              |
              v
┌──────────────────────────────┐
│      CURRENT (AMPS, A)       │
│ (Amount of flow of electrons)│
└─────────────┬────────────────┘
              |
              v
┌──────────────────────────────┐
│     RESISTANCE (OHMS, Ω)     │
│  (Opposes current flow)      │
└─────────────┬────────────────┘
              |
              v
┌──────────────────────────────┐
│        POWER (WATTS, W)      │
│  (Total energy used or made) │
│    W = V x A                 │
└──────────────────────────────┘
  • Voltage (V): the “push” behind electricity
  • Current (A): how much electricity is moving
  • Resistance (Ω): how hard it is to move electricity
  • Power (W): the total work being done

SERVICE DROP

  • The service drop is the overhead wiring from the utility pole to the house.
    • Sometimes called “overhead service.”
    • If underground, it is called a service lateral.
  • A splice joins wires together and these are found where the service drop or service lateral ends.
  • A drip loop (U-shaped bend) is used to prevent water from entering the service entrance.
  • A three-wire service drop (single-phase) is most common in houses:
    • 2 hot wires (typically black)
    • 1 neutral wire (white, or sometimes black as well)
    • Neutral may also act as support.
  • If only two wires are seen, it is usually an outdated 120V system needing replacement.
  • Four-wire service (three-phase) is common in commercial or large farm buildings and is not covered in residential inspections.
  • Typical residential service is 240V single-phase from a three-wire drop.