When it comes to surge protection, any point of entry into your home where a surge can damage your electronics must be protected. This includes phone lines, satellite lines and cable connections for modems. Installing a modem surge protector can protect your computer from the damaging effects of a power surge. You see, modems are more prone to surges than normal power lines. Having a surge protector for modem and coaxial connections will protect both the delicate microelectronics within the modem from surge damage and will block that surge from entering your computer. You should already have computer surge protection installed to protect the lines on the mains.
What makes it so easy for a surge to travel through your modem line? A differential surge, as it’s called, moves the same effortless way along the coaxial line as the signal for your Internet connection. To have the best protection possible without unplugging everything connected to the coax line you need to have install protection on both sides of the line transformer. For the side nearest the line it’s best to have a gas discharge tube (GDT) surge protector. This acts as your primary defense. The next type is zener diodes which should fit behind the GDT to absorb what gets through the line from the transformer.
Your transformer will keep out most common mode voltage. But with its limited isolation capabilities you need modem surge protection for the higher voltages that can come through the connection. In order for this to work properly, however, you need to ensure that your modem is properly grounded. Otherwise over-voltages will not be stopped. Not being grounded correctly will negate any surge protector you introduce on the coax line. It’s also a matter of user safety and is why most modems don’t utilize surge protection.
Nonetheless, when it comes to protecting expensive computer equipment from data loss, it is worth it to ground your modem and install a modem surge protector. You can minimize lightning surge damage if the strike isn’t focused locally. No form of surge protection will stave a direct strike. With proper earth grounding coax lines and modems can be protected which in turn means your computer and any data within it is protected from sudden and catastrophic loss.
In a lightning strike, a surge travels down the power line where it should hit the grounding block and cease to exist right there. That’s true only if the earth ground is sufficient to disable such a strike. Lightning is attracted to your mains electricity, or the AC lines coming into your home. All conducive lines coming into the home must be tied in to the main earth ground or the lightning surge will find a way in and cripple your electronics if not right out destroy them.
With the case of degrading a signal, if the cable modem surge protector comes as part of a larger all-in-one protector most cable companies recommend not using one of these surge protectors to protect your modem connection. A plug in model is not effective against a coax line surge. These devices do not block or absorb radio signals. Your result is loss of protection on the coax line or signal degradation, or both.
The reason you need coax surge protection in the first place is that the grounding block only covers you at the shield. Modem surge protectors cover the center conductor line as well. That said, it’s typical that if the surge is blocked at the shield then you won’t have to worry about a surge inside the coax line. The thing with wall surge protectors is that they don’t provide protection for the center line; they only degrade the signal. They are also too far away from the earth ground to provide sufficient protection from a surge entering the coax line. You need a surge protection device that is designed for centerline protection. Most modem surge protectors are made for this. A good product to look into is Polyphaser, who specialize in coaxial surge protection.
Surge protection installed and sized proportionately to the appliance needing protection will provide sufficient protection from surges, which exist on a daily basis. It is completely normal to experience several power surges in your home every day.
Of course the best and only complete protection from sever power surges on your coax line or your mains electricity is to unplug the appliance at risk. In the case of a DSL modem surge protector, when it is turned off and on the communication between the modem and the coaxial cable line sync to regain a connection. This happens quite fast. The only problem with unplugging the modem surge protector is that you can miss important data stream downloads from your Internet supplier. In this case it is best to leave the DSL modem surge protector turned on and plugged in at all times.