Purpose

• Surge suppressors intercept spikes, surges and sags in the electricity going through them. Spikes are extremely brief pulses of less than three nanoseconds in length, but surges are pulses lasting three nanoseconds or longer. Lightning strikes rank as the most common source of damaging surges, but your household voltage fluctuates throughout the day. Surge suppressors also can prevent damage, called sags, caused by voltage drops in your incoming electrical feed.
  
  

Power Surges

• Power surges come in two main types. An external surge enters your home or business circuitry from the main power lines, such as a bolt of lightning or a malfunctioning electrical transformer. An internal surge, created within your home or business, could be caused by high-voltage machinery turning on and off, such as a large air-conditioning unit in a home with old wiring, or factory equipment used intermittently throughout the day.
  
  

Types

• Among two primary types of surge suppressors, the first and oldest type -- a shunt mode suppressor -- works by channeling a detected surge through dampening circuitry or a fusible link. The second type, called a series mode suppressor, monitors the power continuously. Shunt mode protectors have to react to a surge and potentially allow some portion of surge to pass through to your electronics; series mode protectors manage the power passed through at all times.
  
  

Combination Suppressors

• Some surge suppressors include connections for cable TV, telephone or network devices, but the more types of input you connect to the suppressor, the greater the chance your devices will be exposed to potentially damaging surges. If your cable line passes through the same suppressor as your electricity, your appliances could become vulnerable to a dual surge, increasing the possibility of the surge suppressor failing.
  
  

Considerations

• The question isn't so much whether you need a surge suppressor, but rather what type of suppressor to use. A series mode suppressor proves critical for sensitive electronics, while stable equipment such as a home stereo are better able to handle the surges that a shunt mode suppressor may let through. You can use series mode for all devices, but be prepared to pay a little more.