Can You Plug a Phone Line Into An Ethernet Port?

One of the most important steps in setting up a network is making sure that everything is plugged into the right place. One situation where this can be confusing is when there are both phone lines and Ethernet cables in the same network. A very common question in this situation is whether or not you can plug a phone line into an Ethernet Port.

Most of the connectors that are commonly used in phone networks can be used to plug a phone line directly into an Ethernet port. This is a great option for anyone who would like to send phone signals down an Ethernet cable. However, you can not send Ethernet signals down a phone line. Ethernet cables are backward compatible with most phone equipment but Ethernet equipment will not work well over a voice-grade cable. It is also important to know that you should never plug an active analog phone line into any Ethernet network equipment as this can damage the Equipment.

What Kinds of Connectors Are There?

Early in the development of analog phone technology every time a phone technician needed to move or change how a phone was connected to the network he or she had to completely re-terminate the wires. This was time-consuming and relatively unreliable. Because of this problem the registered jack was created. As networking requirements expanded over the years so to did the registered jack.

Early on the RJ-11 jack was used to connect phones that only had one line. Later the RJ-14 became more popular as phones with two lines became more commonplace. Today typical Ethernet cables are terminated using the RJ-45 jack. There were other members of the registered jack family but these are the most common today. Check out the table below to get a better idea of how these different connectors compare to each other.

Jack NameConnector WidthNumber of PinsNotes
RJ-1162Used for single line phones
RJ-1464Used for two line phones
RJ-2566Used for three line phones
RJ-4884Used for four wire data lines such as DSX-1, DDS, and DS1
RJ-4588Standard Ethernet Connections
Common Registered Jack Styles

As time went on and the need for additional bandwidth from a single cable became greater phone cable manufacturers started creating cables with more wires inside of them. The cables with more pairs of wires came with the requirement of wider registered jacks that provided the space to be able to terminate these additional wires. When these new wider jacks were created the designers chose to make sure that they were all backward compatible with each other. This was so that people would still be able to plug their old single-line phone into a jack that was larger and able to accommodate multi-line phone equipment.

This image shows an RJ-14 connector next to an RJ-45

Today we are left with a situation where all of the most common legacy registered jacks will plug right into even the newest of network cables and network equipment. This is a great feature for people who are looking to use older phone equipment on a brand new cable. For other people, however, this situation can cause quite a bit of confusion.

When is it Okay to Plug a Phone Line Into an Ethernet Cable?

The main reason that someone might want to plug a phone line into an Ethernet cable is to be able to use that cable to extend the phone line to another location in the building. A very common example of this is when someone would like to move their DSL modem to another room in the house. To be able to do this all you need is any cable that is as good or better than a typical phone line. Ethernet cable is more than up to the task. In this situation, there is absolutely nothing wrong with plugging the DSL phone line into one end of the Ethernet cable as long as you are sure that only the modem is plugged in on the other end.

I sometimes run into people who have an old phone line in their home that they would like to use as Ethernet. While you can not use a voice-grade phone line to connect two Ethernet network devices reliably there are some situations where it can be made to work with minimal modification. I wrote a whole blog post that explains in detail how to know if your network can be modified and how to do the work.

When is it Okay to Plug a Phone Line Into Network Equipment?

One of the most important things to understand when thinking about mixing phone lines with Ethernet cables and equipment is to understand that there are situations where network equipment can be damaged by a phone line. The reason this can happen is because of the relatively high voltage spikes of electricity that are sent down a phone line when it is ringing. These high voltages do not typically happen in an Ethernet network and not all Ethernet equipment is designed to handle these spikes.

Because of this risk, it is extremely important that you never plug a live analog phone line into any network port that is not designed to handle it. In most residential networks the only equipment that will be plugged directly into a phone line will be actual analog phones, DSL modems, and security systems. There are a few other things that might require a phone line but these three the by far the most common. At the end of the day just be sure that whatever device you are plugging into a phone line is designed to accept the signals that might come down it even if that phone line is extended across your house with an Ethernet cable.

Conclusion

Ethernet cables are backward compatible with most legacy registered jacks including the common RJ-11 and RJ-14. There is absolutely nothing wrong with using this feature to allow you to extend phone lines to different locations in your home. If you do so just make sure that you do not plug any equipment into that phone line that is not designed to use it.