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*Read Me* How to perform an Isolation Test

So, you are on ADSL or ADSL2/2+ and are having some problems. Usually, someone here will ask you to perform an Isolation Test


So what is an Isolation Test?

An isolation test is when you remove all devices that connect to your phone line. These include ADSL filters, phones, faxes, answering machines, Foxtel Digital (or any other Digital PayTV) set top box, EFTPOS machines, back-to-base alarm systems, dialup modems, medical alerting systems etc – basically anything that plugs into the phone line. In some cases, you can even have Soft Drink Vending Machines and other fun and quirky items connected to your phone line, so it pays to check!


Important Note: DO NOT, under any circumstances, remove anything that is "hard wired" into your house unless you are an approved Electrical Technician that has an AUSTEL Licence. Please also note the Important Disclaimer at the bottom of this article.


The purpose of removing all devices from the line other than your Modem is to eliminate any potential issue caused by equipment in your house. In my experience, these are a frequent source of problems.


After all devices have been removed, plug your modem directly into the first phone socket into the house, bypassing any filters or splitters (just to eliminate these as a possible problem).


The first socket is generally the one in the common area of the house, however can vary depending on the setup of your house. If you aren't sure which is your "first" socket, simply test all sockets in your house.


Always make sure when performing an isolation test that you use the shortest possible phone cable, preferably one that's 2-3m long. In some cases, it might be a good idea to try a brand new cable, however you don't need to do this right off the bat.


In some cases, some of your phone points may not have ADSL, either as a fault or by design. That's why its important to test all sockets if the first socket doesn't work. If the Internet connection works on a single socket, it is your responsibility to arrange for the work to get that 2nd socket working, as Telstra is only responsible for the first socket.


Monitor the Internet connection for the difficulty you were experiencing to see if it clears. If the problem is still there, refer to the notes below.


If the difficulty you were experiencing clears, then simply reconnect ONE piece of equipment at a time back onto the line, starting with your ADSL filter (if applicable). Monitor for the issue between each part, and see when it presents itself. If the problem recurs, then logic dictates that the problem is with the devices that were most recently connected.


But I don't have any issues/This is a pain, why do I need to do this?
If you are having issues with things like your connection dropping out, noise/static on your phone line, slower speeds than usual, then this test can help to pinpoint the issue and will be useful if you need to contact your ISP to report a fault.


All these issues are often caused by some form of interference induced into line, which could be a result of bad filters, dodgy phone cables, malfunctioning telephony equipment, or even nearby electrical devices.



  1. If after you have done all this and still having issues, it isn't always a problem with your line outside your house. It very well could be an issue with your internal wiring (eg. a mouse could've chewed the wires in your roof). Issues can also arise with corroded cabling/sockets, problems with hardwired equipment that can't be removed (alarm systems, wall mounted phones, ringer bells), or internal cabling that won't support ADSL due to faulty installation – the latter is why you try all the sockets.
  2. If after you have done all this and still having issues, it isn't always a problem with your line outside your house or your internal wiring. It may be possible that your modem has gone faulty and would be good if possible to test with another modem.
    If you have completed your isolation tests and still have no Internet connection, an unstable connection, or a poor speed issue etc, it's time to escalate the problem to your Internet provider and let them launch an investigation for you. It's in your best interest to complete this process first though for several reasons:
  • If the problem is on your end, you can clear it quickly yourself. Don't forget, for most customer there isn't any legal or contractual need for your Internet Company to fix an issue, and sometimes issues can take days, if not weeks to resolve, depending on workload.
  • Your Internet company will likely ask you to perform these tests anyway. It will save you time on the phone to Technical Support if you tell them you have done this, and that it still didn't work.
  • If a Telstra tech finds the problem is beyond Telstra's Responsibility, they may charge you a fee in addition to leaving the problem as is and walk away. This is because any and all wiring, sockets, equipment and connections that are past Telstra's responsibility are your privately owned equipment, which Telstra will not service. Doing your isolation test thoroughly eliminates this as an issue, protects you from being charged this fee, and allows you to correct any issues with your own equipment more quickly than waiting for a Telstra tech to do so.

Important Disclaimer: Use common sense when performing these tasks. If you aren't sure if you should be doing something, then don't do it and contact your Internet Provider. It is better to have someone come out and professionally look at the issue (with a potential charge) over injuring or killing yourself.


Original text supplied by Whirlpool and modified for CrowdSupport.


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