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Phone Jack Arc Spark

Posted by grandmum (My Page) on
Mon, Sep 26, 11 at 13:41

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?


Follow-Up Postings:

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RE: Phone Jack Arc Spark

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.


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RE: Phone Jack Arc Spark

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.


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RE: Phone Jack Arc Spark

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.


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RE: Phone Jack Arc Spark

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.


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RE: Phone Jack Arc Spark

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


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RE: Phone Jack Arc Spark

"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.


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RE: Phone Jack Arc Spark

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.


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RE: Phone Jack Arc Spark

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.


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RE: Phone Jack Arc Spark

"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.


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