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).
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.
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.