Home » Blogs » Industry Blog » Type I+II DC Surge Protection: When Do You Need Class B+C SPD Protection?
2026-08-18
When Does a DC System Need Type I+II Surge Protection?
As more solar PV systems, battery storages, telecom power networks, and industrial DC equipment are added, surge protectors become a necessity to protect DC circuits against lightning and transient overvoltage. Not every installation needs the same surge protection, though.
One of the most common selection questions is:
Should the system use Type II DC Surge Protection, or is Type I+II DC Surge Protection required?
The answer depends mainly on where the DC circuit is installed, how exposed it is to lightning events, and how critical the connected equipment is.
A Type II SPD provides some protection against internal equipment from induced surges. But for DC systems with outdoor cables, solar arrays, battery storage systems, and exposed communication systems, surge energy can enter from external lines. For these systems, direct current systems require chained-type protection against lighting currents and limiting transient voltages.
Knowledge of Type I, Type II, and Type I+II DC Surge Protection
DC Surge Protection devices are classified by the surge conditions they address.
Type I DC Surge Protection Devices: For High Energy Lightning Conditions
Lightning protection on the incoming side of an outdoor DC circuit requires a Type I SPD.
It is tested with the 10/350μs current waveform, which represents the high-energy and long-duration characteristics of direct lightning strikes.
Typical applications include:
•Outdoor PV DC systems
•DC distribution points exposed to lightning
•Remote installations with long cable routes
Type I protections primarily serve the function of excess voltage energy dissipation. However, they do more. Type I protections provide surge protection and help safely divert a significant portion of a lightning surge away from the protected system.
Type II SPD: Protection Against Transient Overvoltages
Type II SPD addresses surge phenomena that are associated with:
•Localized lightning
•Switching
•Inductive load variations
They are tested against the 8/20 μs waveform, which represents faster transients of overvoltages.
Typical applications include:
•Internal control cabinets
•Equipment-side protection
•Secondary distribution panels
Type II protection works best when the surge energy has already been reduced. However, it lacks sufficient protection to be directly exposed to lightning current.
Type I+II DC Surge Protection: Combined Protection for Higher-Risk Systems
A Type I+II DC Surge Protection device integrates the functions of both protections:
•Type I capability for high-energy lightning current
•Type II capability for repeated transient surges
As such, it may be deployed on systems where surge exposure is undefined or where the consequence of equipment outage may be significant.
| System Condition | Recommended Protection |
| Indoor DC equipment with limited surge exposure | Type II SPD |
| Outdoor DC cables with moderate lightning risk | Type II or Type I+II depending on installation |
| PV arrays, battery storage, telecom outdoor systems | Type I+II DC Surge Protection |
| Critical DC infrastructure requiring maximum reliability | Type I+II DC Surge Protection |
When tp Choose Class B+C SPD Protection?
In IEC terminology, Class B+C SPD refers to the combination of Type I and Type II protection functions.
Protection class B+C should be used depending on the entire system rather than based on the level of DC voltage:
•Long dc cables will have induced voltage due to lightning,
•Farther away equipment will have more exposure to environmental voltage due to the open atmosphere,
•Sensitive equipment will not be able to withstand high voltages,
•It may be costly to replace the equipment and have downtime
A base station communication unit that is a 48V DC system may operate at relatively low voltages. However, a surge can disrupt communication services. Control circuitry may also be expensive in battery storage systems that require net surge protection.
How to Match Type I+II DC Surge Protection with Real Applications
Solar PV Systems
Type I+II DC Surge Protection has numerous applications, and solar energy systems are one of the more common of these applications.
With PV modules typically being installed outdoors, combined with the long branch wiring, there are significant DC circuits over great distances within PV solar installations. These long distances create a primary pathway for surges generated by lightning.
Type I+II DC Surge Protection is typically used for protection of:
•PV string circuits
•DC combiner boxes
•Solar inverters
•Energy management equipment
Battery Energy Storage Systems
Battery storage systems include DC battery packs along with power conversion and control equipment, and monitoring electronics,
Surge protection is needed due to:
•DC battery cables can be long and run through large installations
•PCS and BMS components are sensitive to overvoltage
•System availability is critical
Telecom and Industrial DC Networks
A number of telecom and industrial systems rely on continuous DC power.
Examples of these include:
•48V communication power supplies
•Industrial control cabinets
•Remote monitoring systems
•Security and automation equipment
For these systems, DC Surge Protection must provide surge capacity as well as ease of maintenance and fault monitoring.
Why GDT-Based Design is Preferred For High Energy Type I+II DC Surge Protection
With respect to Type I+II applications, the SPD is required to absorb a significant amount of surge energy. Gas Discharge Technology (GDT) is used quite extensively due to benefits such as:
•High energy capability
•Low leakage current
•Excellent insulation
•Dependable and repeatable surge performance
Telebahn's DC Surge Protection focuses on High Energy GDT technology for the more demanding DC applications. The products provide Type I+II (Class B+C) protection with surge ratings of 25kA Iimp (10/350μs) and 25kA In (8/20μs) for applications requiring strong discharge capability.
Considerations for Type I+II DC Surge Protection
When selecting SPDs, installation considerations are given as much importance as selection.
The primary considerations are:
•Location: Install SPDs within the lightning protection zone
•Design: Minimize length of connections to reduce residual voltage
•Design: Provide proper connection to ground potential
•Design: SPDs should be operated in conjunction with backup devices
•Monitoring: Provide status monitoring for the critical system
Telebahn has palm DC Surge Protection Devices with DIN rail mounting and pluggable modules for maintenance and thermal disconnection with an optional remote contact alarm.
The Right Type I+II DC Surge Protection Devices
A more important question should be:
"What level of surge protection is required by this DC system?"
In the presence of outdoor wiring or operation in harsh and transient environments and/or in the presence of lightning, Class B+C Type I+II DC Surge Protection covers both high surge energy and transient protection.
Telebahn builds surge protection designs for renewable energy, telecom, control, and other DC power systems by combining several technologies: high-energy GDTs, modular construction, and application-focused DC protection solutions. It is important to select the proper level of protection in the design phase to reduce system failures and improve long-term system availability.
FAQs
Q1. What is Type I+II DC Surge Protection?
Type I+II DC Surge Protection combines transient surge protection and lightning current protection, and is designed for DC systems that deal with outdoor wiring, face threats of lightning, or contain sensitive equipment. Some example applications are solar, storage, and telecommunication.
Q2. Why pick Class B+C SPD protection over Type II DC Surge Protection?
Unlike Class B+C SPD protection, Type II DC Surge Protection is only capable of protecting against transients and surge inslabulation events. More importantly, Class B+C SPD protection is capable of protecting equipment from larger energy lightning strikes.
Q3. Which applications can employ Telebahn DC Surge Protection products?
Telebahn designs its DC Surge Protection products for the following applications:
•Solar PV systems
•Battery energy storage systems
•Telecom DC power networks
•Industrial automation equipment
•Remote DC power installations
Q4. For which applications do Telebahn Type I+II DC Surge Protection devices offer protection?
Telebahn's Type I+II DC Surge Protection products have been designed for demanding applications that require high surge discharge capability (up to 25kA Iimp with a 10/350μs waveform, and 25kA In with an 8/20μs waveform).
Q5. What Indicates that Telebahn uses GDT technology in DC Surge Protection devices?
Gas Discharge Tube technology is designed for high energy discharge capability, low leakage current, and strong surge resistance so that it is suitable for high risk protection of DC systems.
