There is a growing need to safeguard electronic systems from the harmful effects of voltage surges. An excellent protection option is Bourns® IsoMOV™ Hybrid Protectors. They are designed to offer a robust solution by integrating the benefits of Metal Oxide Varistors (MOVs) and Gas Discharge Tubes (GDTs). A helpful white paper from Bourns provides a comprehensive guide to selecting the appropriate IsoMOV™ component based upon your system’s specific needs. Below is a summary of the valuable information readers will learn.

Steps in Determining the Right IsoMOV™ Protector

Step 1: Assess Your System’s Voltage and Type

• AC vs. DC Power:
  • AC Systems: Often experience higher frequency transients.
  • DC Systems: Typically, lower voltage but can be susceptible to longer-duration surges.
• Nominal Voltage Rating:
  • Maximum Continuous Operating Voltage (MCOV): Ensure the IsoMOV™ protector’s MCOV exceeds the system’s nominal voltage to prevent unintended triggering.
  • Safety Margin: A recommended guideline is to select an MCOV approximately 1.1 times the system’s nominal voltage.
• UL 1449 Compliance and LCAOV:
  • In AC networks prone to frequent overvoltage events (swells), take into consideration the Limited Current Abnormal Overvoltage (LCAOV) rating.
  • The LCAOV parameter indicates the device’s tolerance to overvoltage for a limited duration (typically less than 7 hours).

Step 2: Identify Surge Requirements

• Assess Surge Current and Energy Handling (I_max & I_nom) Needed:
  • Bourns offers multiple IsoMOV™ protector models with varying surge current capabilities from 3 kA to 8 kA.
• Determine Likely Surge Sources:
  • Lightning Strikes: Direct or indirect strikes can generate high-energy surges.
  • Switching Transients: Electrical switching operations can cause transient voltage spikes.
• Evaluate Surge Frequency and Intensity:
  • In environments with frequent switching events (e.g., industrial settings with large motors), designers are advised to select an IsoMOV™ protector with a higher energy handling capacity.

Step 3: Evaluate Energy Absorption Capability

• Energy Handling:
  • Surge Energy: Assess the energy levels of potential transients and surges.
  • Surge Frequency and Duration: Consider the frequency and duration of surge events. Repeated high-energy surges can impact the device’s lifespan.
• Select the Right Energy Rating:
  • High-Energy Environments: For applications in certain harsh environments (e.g., outdoor installations, thunderstorm-prone areas), it is recommended to use Bourns® IsoMOV™ Model IsoM8 with higher energy absorption capacities.
  • Energy Rating Unit: The energy rating is typically measured in joules (J).
  • Lifespan: A higher energy rating ensures longer operational life, especially in environments with frequent surge events.

Step 4: Consider Clamping Voltage and Let-Through Voltage

• Clamping Voltage (Vc):
  • This is the maximum voltage the IsoMOV™ protector allows during a surge.
  • Ensure the clamping voltage is low enough to protect sensitive components without causing damage.
  • Clamping voltage can increase with higher surge currents.
• Let-Through Voltage (Vfp):
  • Due to an IsoMOV™ protector’s hybrid nature, the Vfp parameter becomes important.

STEP 5: Application-specific Requirements

AC Power, DC Power, and Motor Drives

• Industrial Applications: Require the ability to protect against AC and DC power surges.

 Motor Drives

• The inductive nature of motor loads can generate high back EMF.

Power Line Communications and Sensitive Electronics

• Protection needs to feature low inherent capacitance.
• Signal Integrity: It is necessary to select an IsoMOV™ model with a capacitance rating that minimizes interference with the communication signal.

DC Applications

 • Solar Power Inverters and Battery-Powered Equipment: DC applications require a surge

protection solution that features an appropriate breakdown voltage to prevent conduction

during normal operation.

 • High-Energy Transients: The protection solution needs to effectively handle high-energy transients commonly found in DC systems.

For more detailed tips of how to select the right IsoMOV™ hybrid protector, engineers are invited to read the full white paper, “How to Select the Right Bourns® IsoMOV™ Component for Maximum Protection”.