Surge Protective Devices (SPDs) are essential for protecting electrical and electronic equipment from voltage spikes caused by lightning, power surges, or switching transients. They come in different types according to their area of application in the electrical system and their level of protections. Here’s a breakdown:
Different Types of SPDs (with IEC 61643 Standards & UL 1449 Standards), categorized based on their installation location and protection level:
1. Type 1 SPD (which also called Class I):
Purpose: Protects against direct lightning strikes (high-energy surges).
Installation Location: Installed at the service entrance (between utility and main distribution panel).
Common Use: Used in buildings with external lightning protection (for example, lightning rods).
Technology: Typically uses spark gap technology for high discharge capacity (for example, 50 kA+).
2. Type 2 SPD (which also called Class II):
Purpose: Protects against residual surges from lightning and switching transients.
Installation Location: Installed at sub-distribution panels (downstream of the main panel).
Common Use: Used for general equipment protection (for example, HVAC, machinery, IT systems).
Technology: Usually MOV (Metal Oxide Varistor) based, with moderate discharge capacity (for example, 20-40 kA).
3. Type 3 SPD (which also called Class III):
Purpose: Provides fine protection for sensitive electronics.
Installation Location: Installed close to the equipment (for example, power strips, outlet-level SPDs).
Common Use: Protects devices like computers, TVs, and medical equipment.
Technology: Often uses MOVs or gas discharge tubes with lower energy handling (for example, <10 kA).
4. Combined Type SPD (Type 1+2 or Type 2+3):
Purpose: Combines two protection levels in a single device.
Example: A Type 1+2 SPD can be installed at the main panel for both lightning and surge protection.
Advantage: Reduces the need for multiple SPDs in some cases.
How to Choose the Right SPD?
When selecting an SPD, there are some aspects to consider:
First, consider from Risk Assessment
Is the location prone to lightning strikes?
Are there sensitive electronics that need protection?
Second, consider from Installation Location
Type 1 SPD for main service entrance (if lightning risk is high).
Type 2 SPD for sub-panels (general protection).
Type 3 SPD for point-of-use devices (like some sensitive equipments).
Third, consider from Voltage Rating
According to the area of application, must match the system voltage (for example, a photovoltaic DC input of 1500V system, or an AC input of 420V system in connection with the load at residence).
Fourth, consider from Surge Current Rating (kA)
Higher kA equals to better protection (for example, 20kA surge current rating for Type 2 SPD and 50kA above surge current rating for Type 1 SPD).
Fifth, consider from Response Time
Faster response (nanoseconds) is better for sensitive electronics.
Sixth, consider from Standards Compliance
Look for IEC 61643, UL 1449, or IEEE C62.41 compliance.
Seventh, consider from Fail-Safe Mechanism
Some SPDs have thermal disconnectors to prevent fire risks if they degrade.
Example Selection Guide
- Industrial plant with lightning rods: Type 1 + Type 2
- Office building with IT equipment: Type 2 (for main panel) + Type 3 (near PCs)
- Home with sensitive appliances: Type 2 at distribution board
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Content editor: Cathy Huang
Email contact: cathy.huang@moreday.com
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