I'm trying to wire up a phone line on my land. I don't care about voice, just about internet (DSL). It's 1.5Mbps, the only speed available.

The TELCO NID is on the same post as the power meter and main panel.

There are several runs of conduit to another post with a subpanel on it. I pulled 250' of UTP Cat5e. I attached one end at the NID, and the other end got a a Leviton Quick Port Voice jack. I plugged in the DSL modem and it failed to connect to the DSL.

Some things I have tried:

  • The box of Cat5e was 500', so the leftovers are the same length as what's underground. I connected it between the NID and the DSL modem, without pulling it all out of the pull box. The DSL modem was able to connect. This eliminates:

    • 250' is too long for DSL

    • I wasn't punching down correctly at the jack

    • I was punching down on the wrong slots on the jack

    • I wasn't correctly attaching at the TELCO NID.

  • I stripped the ends of the blue pair and twisted them together. At the other end I verified continuity in that pair with a multimeter. The wire is not broken.

I have not tried plugging in a regular handset to check for a dial tone, since I don't own such a device. I will borrow one and add the results to this post.

My best guess right now is electromagnetic interference in the trench caused by the subpanel's feeders. The conduits may not be 1' apart. I wasn't here when the trench was filled, so I'm not sure. If this is the problem, would STP work?

EDIT I tried an experiment to eliminate underground interference from the feeder wires. I would turn off the subpanel's main breaker and see if the DSL could connect.

For power I used the inverter in my truck. I plugged the DSL modem in to the inverter and it was able to connect to DSL. The subpanel was still on at this point. I am surprised this worked. I immediately plugged the DSL modem back in to the subpanel's receptacle and it failed to connect to DSL. Weird.

I tried switching the breaker for that circuit to the other leg of the electric service, and that worked, too! It seems to work about 50% of the time this way. Weird.

What should I try next?

  • does the DSL 'connect' at the point you are putting the wires in? you know the other end?
    – Piotr Kula
    Jul 4, 2011 at 8:48
  • @ppumkin: If I plug the DSL modem directly in to the NID, it works.
    – Jay Bazuzi
    Jul 4, 2011 at 16:27
  • 1
    An 250' run of unshielded comm cable directly next to feeder AC cables sounds like a recipe for massive interference. Try it with a wired phone, you may be able to hear the interference on the line. STP would probably help, but the ideal solution would be to run comms and power in separate conduit. Jul 4, 2011 at 19:18
  • @ShimonRura: They are in separate conduit, but the conduits were probably not separated carefully in the ditch before backfilling. I was hoping that Cat5e's design would be sufficient to carry 1.5Mbps DSL, but maybe not. Thanks.
    – Jay Bazuzi
    Jul 4, 2011 at 21:05
  • you might need to bridge the negative from the AC and the shield of the CAT5E... and perhaps use a ground loop isolater. But also i am not 100% sure now i think you need to use a Diode or High resistor to bridge the AC to the CAT5E Shield to avoid voltage spikes on Negative... other wise you could use a spare wire from the cat5e to act as a aerial and use a device to eliminate noise (but i think they are a bit pricey)
    – Piotr Kula
    Jul 4, 2011 at 21:12

1 Answer 1


STP should help. Just make sure to ground it properly, or the interference can be worse - like a long antenna.

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