I recently rented an apartment that is part of a larger house. My landlords have Comcast high speed Internet service. The cable in my apartment is an extension of their cable wiring. They didn’t want to share their wireless network, so I needed to install my own cable modem.

Is a second cable modem without independent cabling from Comcast possible? A quick web search revealed mixed opinions that struck me as unreliable. And of course, Comcast’s own support site had nothing useful to say about it. So I just had to dive in and give it a try!

The short version

1. Get a cable modem. You can lease one at a Comcast store and set up your account at the same time, but that’s not what I did. I bought a Motorola SB6120. It implements DOCSIS 3.0 and is compatible with Comcast. You can use any cable modem on the compatibility list.
2. Connect the cable modem and let it sync until you get steady Power, Receive, Send, and Online lights.
3. Write down the MAC ID found on the bottom of the cable modem.
4. Call Comcast customer service at 1-800-266-2278 and set up a new Internet-only account. I got a special rate for the first year.
5. Customer service will transfer you to tech support. Read them the MAC ID. They will provision the modem while you wait.
6. You are now online!

A twisty maze of passages, all alike

Here’s the full story of how I developed this procedure through a series of discoveries and false starts. There’s a lot more explanation than the short version. I describe what I learned from each dead end. The only steps you need to follow are in the short version above.

You have the choice of supplying your own cable modem or renting theirs. You can pick one up at a Comcast store and set up your account at the same time. I elected to buy my own, which enabled me to do everything over the phone. Comcast has a list of cable modems they have certified as compatible with their system. I chose the Motorola SB6120 based on its easy availability at Best Buy and its solid reviews there and at Amazon.

The first thing I tried was connecting the cable modem and starting a browser. After waiting a few minutes until the Power, Receive, Send, and Online lights were on and no longer flashing, I opened my browser and got a Comcast activation page. I entered my landlord’s account number. It then told me to download and run the Comcast Installer Wizard. It dragged me through a long process, only to tell me, “An existing High-Speed Internet cable modem has been detected on your account.”

I took the choice, “I am adding an additional cable modem.” It then dumped me out with, “In order to add an additional cable modem to your Comcast account, please call 1-800-COMCAST for assistance.” This message doesn’t mean what it says, though, because when you call, you will find out that you can’t add a second cable modem to the account. You have to open a new account.

I called 1-800-266-2278 and got customer service on the line. (I started with tech support, based on the misleading message above, but they eventually transferred me to customer service.) The person I talked to did not understand the second cable modem issue very well. Just tell them you are adding a second cable modem and need to open your own account.

At first, they tried to foist a $50 “activation fee” on me. Don’t fall for it. Tell them you have your own cable modem and don’t need any help installing it. It’s all synced up and ready for them to bless it. That reduced my “activation fee” to $2. Whatever. I got a special discounted rate for the first year of service, month-to-month with no contract.

The customer service representative will give you your new Comcast account number. Be sure to write it down, because you’ll need it if you require help later.

Next, you get punted to tech support to provision or “activate” your service. They will ask for your cable modem’s MAC ID. You will find it on a sticker on the bottom of the cable modem. With that, and your account number, they will reach out and program your cable modem remotely. This takes a few minutes and restarts the modem. After that, you should be ready to go. Try pulling up a web page to test the connection.

If you arrived here after trying the Comcast Installer Wizard, you may find (like I did) that it left behind HTTP proxy settings in your browser that will now prevent it from working. (Thanks, guys!) If your browser no longer works, look through your browser settings for a proxy server with “comcast” in the name and delete it.

After fixing my browser, the connection worked perfectly. If I had been able to find out what I’ve written here before I started, the whole process would have taken less than half an hour.

Why is this fair?

Why is Comcast charging you for a whole extra account at the same location? I can’t speak for Comcast, but I may be able to shed some light on this. Cable Internet differs from DSL (telephone) Internet service in that all customers in a neighborhood share a common cable. As far as Comcast is concerned, you are a separate customer needing your own account, even though you might be located in the same house as another customer. After all, you’ll be using a certain chunk of bandwidth like every other customer.

Continue the conversation

I hope this article shed some light on how Comcast handles two cable modems in the same house. It is based on my own experience in California as of May 2011. If you had a different experience, I’d love to hear about it in the comments, so everyone can benefit.