Phone Jack Arc Spark

grandmumSeptember 26, 2011

Hi- I was in a dark room with that has an unused phone jack on the wall. When a call / ring came in I saw a tiny arc inside the jack.... should I be concerned with this? Is this normal?

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weedmeister

Probably dirty.

When the phone rings, there is a 130VAC signal applied to the line. It only occurs when ringing. The rest of the time it is 50VDC.

    Bookmark   September 26, 2011 at 2:12PM
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grandmum

Thank you for letting me know its 130 when ringing.

My son swapped it out (took the phone off the hook when swapping) blue wire to red wire on jack white with blue to green wire on jack.

No more spark, the four blades on the inside of the old jack were black not copper colored.

    Bookmark   September 26, 2011 at 3:42PM
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Ron Natalie

Ring voltage is 90V 20 Hz AC. The "battery" power to drive the phone is 48V DC.

Most likely the wires were just too close together. Moving the wiring around fixed the issue.

    Bookmark   September 26, 2011 at 3:49PM
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bus_driver

I always understood that the ring voltage is 90. Fun if you are working on the system and holding the conductors when someone calls in.

    Bookmark   September 26, 2011 at 9:38PM
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Ron Natalie

Not much current however. Won't kill you, but it does get your attention.

    Bookmark   September 26, 2011 at 9:40PM
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brickeyee

"Not much current however. Won't kill you, but it does get your attention."

The available current will depend on how close to the central office you are.

If you are close and have a lower local loop resistance it can approach dangerous, but you still need to be across the lines or the ground resistance so so high it will be harmless.

    Bookmark   September 27, 2011 at 9:38AM
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Ron Natalie

Not so much the distance from the CO but how the CO equipment limits the current. Usually they won't source more than about 40 ma (about enough to ring 5 old style bell 2500 desk phone mechanical ringers). Most modern phones don't pull even 1 REN (ringer equivalence number) so it's quite possible they don't even provide that much these days.

In fact, in my house, there's no electrical connection to the CO at all. The phone stuff comes in via fiber and the ONT in the basement generates the analog battery and ringer voltages.

    Bookmark   September 27, 2011 at 10:29AM
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weedmeister

The equipment I worked on (Alcatel) was 130v in the CO and 40Hz, though the ring frequency was selectable and provisionable. We routinely provisioned up to 4 numbers on the same line with different ring frequencies and supplied ring filters for the phone sets.

    Bookmark   September 27, 2011 at 3:00PM
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brickeyee

"Not so much the distance from the CO but how the CO equipment limits the current. "

Local loop resistance gets very large for larger distances.

The current limiting does work on lower loop resistance.

    Bookmark   September 27, 2011 at 3:34PM
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