Mysterious analog trunk seizure

[Anonymous]

I have a 7100 at a customer premise that occasionally seizes one of the analog lines and will not release it until physically disconnected from the jack.  Once it is reconnected, the unit operates as expected until it seizes the line again.  It's an annoyance, and I haven't been able to pin down the issue, as it is intermittently happening.  Does anyone know of a potential reason for this?

[jayh]

Verify that the 7100 is connected to earth ground, preferably to the same grounding point as the incoming telco protector at the demarcation point. Reversing the polarity of the line may also help. It could be bad hardware. If you swap the problem line with a different one, does the problem follow the wiring or stay with the physical port?

[Anonymous]

Thanks for the response.  We moved the problem line to a different FXO port, and the behavior moved with it.  Someone is supposed to investigate the grounding situation today.  Would the fact that the line is bridge-tapped potentially contribute to this?  I'm guessing it's not helpful.

[jayh]

Bridge taps shouldn't be an issue for POTS. Is the on-hook voltage roughly 50 volts? Try rolling tip/ring polarity. If the trouble followed the line and other FXOs are working fine, it's likely a carrier issue.