Precautions Always disconnect devices Some devices store charge in a capacitor Never connect yourself to a ground wire

Units Amp - The rate of electron flow past a point in one second

• "The diameter of the hose"

Volt - Electrical "pressure" pushing the electrons

• "How open the faucet is"

Watt - Measures electrical load - "How much energy is being consumed?"

• Watts = Volts * Amps

Current Alternating current (AC)

• Direction constantly reverses
• Distributes electricity efficiently over long distances
• Frequency is important
  • 110-120 V of AC (VAC) at 60 Hz in NA
  • 220-240 VAC at 50 Hz in EU Direct current (DC)
• Current moves in one direction with constant voltage

Power Supplies

• Devices commonly use DC that is converted to AC by the power supply

UPS (Uninterruptable Power Supply)

• Short-term backup power
• Blackouts, brownouts, surges
• Common types:
  • Offline/standby (turns on upon blackout)
  • Line-interactive (senses voltage drop and increases power)
  • On-line/double conversion (always running from batteries that are charged by power source)

PDU (Power Distribution Unit)

• Rack devices with multiple outlets that include remote monitoring and control