Obi Connected to House Telephone Wiring Reverses Polarity???

[robhouston]

I've noticed something that I'm not sure is a problem, but it certainly confuses me.  I've installed my Obi110 with my PSTN line coming directly into the Obi LINE port (from a closely located dedicated PSTN line jack).  All house telephones are connected to the Obi PHONE port through another jack I installed that is isolated from the PSTN line.  In everyday use, everything works fine.

However, I noticed that whenever the Obi is powered down, and the phones are connected directly through the Obi to the PSTN line, the polarity of the phone jacks is reversed.  I confirmed this behavior by using a cheap green/red light telephone jack polarity tester after confirming that I've wired everything correctly.  In other words, when the Obi is powered up, the polarity is correct (green light), but when the Obi is powered down, the polarity is reversed (red light).  Either way, the telephones work as expected.

So, is this really a problem, and why would the polarity be reversed by the Obi?

Thanks!

[RonR]

Polarity is not generally a problem.

I just checked with the OBi powered down and it does not transpose the Tip/Ring connections between the LINE and PHONE jacks.  Therefore, it's your incoming PSTN line that's reversed.  Swap the Tip/Ring connection on the pair coming from the PSTN and you'll have a green light on your tester at all times.

If you have a female-to-female coupler anywhere on the PSTN line, they will actually reverse the polarity also.

[robhouston]

RonR:

Thanks for the fast response!

Actually, I double-checked the incoming PSTN line, and up until it connects into the Obi, the polarity is correct. 

However, you've just given me a clue------I don't have any female-to-female couplers anywhere on the PSTN line, but I use a very short telephone line cable to connect the Obi LINE port to the PSTN jack (effectively, it's a male-to-male coupler), and I wonder if that somehow reverses the polarity.   I'll need to check that out.

Thanks again,

Rob