RJ-45 Ethernet surge protection

I have earlier written about Lightning protection and ADSL overvoltages and protection in this blog. And I have published several surge protection documents at ePanorama.net documents section.

What about Ethernet line surge protection? Ethernet ports as they are are pretty well protected as they are compared to many other computer ports: Ethernet ports are transformer isolated with at least 1500 VRMS (2250 VDC) isolation levels, compable in isolation to traditional telephone line modems. Usually this is enough, but not always. According to Ethernet to Ethernet Grounded ESD Protection and Performance Loss with Ethernet Surge Protectors and VARITECTOR DATA CAT6 articles there are cases where adding extra protection is a good idea. According toPerformance Loss with Ethernet Surge Protectors article the use of surge protectors to protect sensitive equipment from lightning hits and surges on Ethernet data lines has become more important than ever with the advent of faster standards like 100 and 1000Base-T Ethernet. The faster data speeds have required equipment manufacturers to use fragile high speed components and Ethernet interface is now integrated onto the main PCB assembly (meaning very expensive to replace when gets damaged).

What kind of circuit is needed to protect Ethernet port then? Littelfuse has publishe a very a good guide for protecting Ethernet circuits. Check also Dehn Ethernet protection white paper.

Let’s take a look at commercial product for for Ethernet surge protection. RJ45 inline surge protector. (with schematic) video by bigclivedotcom takes a good look inside a common inline RJ45 network cable surge suppressor. This device is designed to shunt any high voltage spikes and transients to ground to protect connected equipment.

The video showed how the device was bought from eBay. The device on the video looks similar to this ST-RJ45 Network Lightning Surge Protector – Grey sold by DX.

Let’s take a look at the circuit diagram:


Why this kind of construction? One reason to use lots of diodes it to reduce the number of the overvoltage protection components (the expensive components in this circuit). The other reason is to minimize the capacitance in the circuit. Protection devices in wide-bandwidth VDSL designs require low capacitance, typically less than 20 pF. High speed Ethernet designs would propably need to be even lower capacitance. The capacitance of normal diode is much lower than typical overvoltage protector component.

In this multi-diode circuit makes all the positive voltage surges go through diodes to one protection component, and negative ones to another. If there is some DC voltage on the Ethernet line (for example Power-over-Ethernet), the voltage on the line will be available between the diodes positive and negative common connections (this would allow you to easily “steal” PoE voltage if you want). The surge protection components voltage is selected so that they don’t start to conduct at normal PoE ethernet voltage levels (typically 48V DC, can be 37-57V DC). So for Ethernet applications this kind of protector should work, but it does not suit to all applications of RJ-45 connector (not suitable for PSTN phone line that uses higher voltage ring signal levels that this protector is designed for).

It seems to be hard to make a surge protection device that does not affect the Ethernet communications in any way. Many promise it, but it seems that not all can fullfill the promise. CAT6 RJ45 Network Surge Protector Test-Prosurge Electronics video shows how many so called CAT6 surge protector on the market actually can not reach the 1000Mbps transmission speed and thus will lower your network speed if you use such product.


  1. Tomi Engdahl says:

    Application note
    100 Mbps and Gigabit Ethernet protection

    The IEC 61000-4-5 standard requires five applications of each polarity on the equipment.
    This standard defines several acceptance criteria depending on the state of the equipment
    after the test (performance still ok, degradation of the performance, damage of the
    Ethernet applications usually recommend the A criterion of IEC 61000-4-5. That is, normal
    performance of the equipment after test.
    The most commonly used standard to qualify Ethernet equipment against ESD is the
    IEC 61000-4-2 standard.

    Generally, Level 4 is required, i.e. the equipment has to withstand 8 kV
    contact and 15 kV air discharge.

    SLVU2.8-4A1 and SLVU2.8-8A1 present a typical capacitance of 3 pF that allow them to be
    compatible with 100 Mbps and Gigabit Ethernet lines since, in this way, they preserve the
    signal integrity.
    Both devices are compliant with the IEC 61000-4-5 Level 2 requirements. That is, they are
    able to withstand a 24 A(8 / 20 µs) surge current. They comply also with IEC 61000-4-2
    Level 4 requirements. That is they can support 8 kV contact and 15 kV air discharges for

    Note that both SLVU2.8-4A1 and SLVU2.8-8A1 can protect 100 Mbps and Gigabit Ethernet

  2. Tomi Engdahl says:

    RJ45 connectors offer built-in power surge protection


    The Xmultiple surge protection RJ45 Series of connectors are designed to protect components which are connected to high speed data and telecommunication lines from voltage surges caused by lightning, electrostatic discharge (ESD), and electrical fast transients (EFT). The Xmultiple RJ45 surgre protection connectors utilizes technology for superior electrical characteristics at 3.3 volts. The capacitance of the connector is minimized to ensure correct signal transmission on high speed lines.

    Features and Advantages

    Integrated RJ45 structure saves board space and
    Increases reliability
    Protects RJ45 as well as printed circuit board and components
    Surge Protection and filtering in the connector package.
    Modular Design so the filter is integrated with the magnetic.
    Available in various Amp ratings
    Surge suppression rating of 60kA
    Power and Protection at the entry point of the printed circuit board.
    1800 watts peak pulse power (tp = 8/20μs)
    Transient protection for high-speed data lines
    Low capacitance for high-speed interfaces
    Low operating voltage
    Low clamping voltage

  3. Tomi Engdahl says:

    Network isolators in medical technology

    A network isolator enables galvanic network separation for medical devices and systems according to DIN EN 60601-1. A network isolator is a passive electronic component and do not require a separate power supply. The galvanic separation of medical devices and the avoidance of leakage currents are an essential aspect of everyday medical practice. Technical devices and patients are protected against potentially dangerous over voltages and static discharges.

    The EN 60601-1 defines different classes of insulation, air and creepage distances, leakage current and grounding depending on the desired MOOP or MOPP level.

    MOOP = Means of Operator Protection, Protective measures for operator and user protection.
    MOPP* = Means of Patient Protection, Protective measures for patient protection, to reduce the risk of electric shock.

    *Patients are at increased risk when coming into contact with electrical equipment and systems. Therefore, higher requirements apply to patient protection (MOPP) than to user protection (MOOP).

    Network Isolators – Answers to frequently asked questions:

    Installation errors, ageing processes, environmental influences or moisture can make cable sheaths brittle or fragile. The unwanted electrical connection to other live parts can lead to high overvoltages and voltage peaks for a short time and lead to a fault within the electrical system.


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