Does a UPS Protect Against Surges on Phone Lines?

By SB •  Updated: 01/02/22 •  4 min read

A small power surge will not fry your devices or even leave any visible damage, but it can cause cumulative damage or electronic rust (corrosion). Surge protectors prevent the degradation of internal microprocessors on your electronic devices by spikes or drops in electric current.

It isn’t just your laptops and TVs that can suffer from power surges — fax machines, cordless phones and answering machines are especially sensitive, and computers with internal modems can be completely destroyed by electrical spikes on the phone line.

How do you protect a phone line from lightning?

Just make sure all your devices are grounded (or completely unplugged during a storm) and you will be fairly well-protected.

Should You Get a UPS with a Built-in Phone Line and Ethernet Surge Protector?

While a UPS (Uninterruptible Power Supply) can condition the power coming into your devices and prevent surges if rated with a proper clamping voltage (330-400 Volts or less), in general you want to avoid surge protectors or UPS’s with built-in surge protectors that have multiple ports (i.e. coaxial, Ethernet, phone).


Because the devices in those ports turn on at different voltage levels:

Should you run an Ethernet cable through a surge protector?

Generally speaking, you really only need surge protection if your Ethernet line travels between two buildings that are on separate electrical systems. Ethernet is a local technology, best utilized in an internal network, inside the building.

So how do you protect your Ethernet cable from lightning?

Use shielded cords and shielded ports for all your devices.

An Ethernet Surge Protector is a surge protection device (SPD) that is inserted inline on an RJ45 CAT6/CAT5/CAT5e cable to prevent damage of electronic networking equipment. Powerful surges that the device protects against include direct lightning strikes, voltage spikes, or PoE over-voltages.

An Ethernet Surge Protector is probably overkill for most households. If you can, make sure your cables are unplugged during a storm and that your electronics are powered down and unplugged from the wall.

How to protect a DSL modem from lightning

Advice for all of your plugged-in devices during electrical storms:

In Summary, Ground Everything

The best place to secure your phone and coax connections is where they enter the house and where they can have a short (less than 10-foot connection) to a buried ground rod.

If you secure phone and coax at the service entrance and protect your electronics with Type 3 Surge Protectors you won’t need to secure the Ethernet connections.

It is not a good idea to rely on the Surge Protector inside a UPS as those have a higher clamping voltage generally in the 650-800 Volt range. This means until the voltage reaches 800 volts, your electronics will be getting zapped.

Do not plug a UPS with an MOV surge protector into an existing MOV-based surge protector for compliance (safety) issues, but you can plug a UPS with an MOV surge protector or an MOV surge protector into a Series Mode filter since the filter does not rely on sacrificial MOVs.

The Series Mode filter kicks in at 121.4 VAC on a 120 VAC line and instead of diverting it and hoping the surge can make its way back through your house wiring to the buried ground rod from the main electrical panel, it completely eliminates the surge.


I've been practicing OSINT and utilizing Linux as my daily operating system for over twenty years. The tools are always changing and so I'm always learning, but helping you understand the value of protecting your own data remains at the forefront of everything I do.