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#628569 - 03/27/19 09:08 PM Low Loop Current - POTS - AT&T/BellSouth  
Joined: Apr 2008
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tenex Offline
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tenex  Offline
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New York
Hello all,

I have a weird issue. I had noticed I could only ring 3 phones on my POTS line after having it installed. On a hunch, I went out to the NID and checked the voltage across T&R at the drop. I saw 35-36 V, and 22.5 mA, which works out to about 1620 ohms resistance.

I expected to see somewhere around 44-48 V, since I'm serviced from an RT on a dedicated pair (pair was conditioned and multis cleared as part of the U-Verse rollout). Loop length according to TDR is about 4400'.

I have a repair visit tomorrow, but I wanted to know if there's a way the RT ports can jack-up their output. I think it's a configuration issue, since the loop itself also has VDSL2 running over it - I had the tech test it for stress and shorts, and it's a darn clean pair. Since the day of the Electrical Engineer Phone Man is over, I wanted to be armed with that option before he starts ripping apart OSP he doesn't understand (or tries to avoid fixing it altogether).

I appreciate the help.

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#628572 - 03/27/19 11:14 PM Re: Low Loop Current - POTS - AT&T/BellSouth [Re: tenex]  
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JBean3329 Offline
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POTS lines use AC voltage to make a ringer ring. If it was DC voltage doing it, your phone would always be ringing with talk battery applied. Low loop current symptoms would be poor/low audio on the line.

Chances are, the total ringer equivalence of your three phones exceeds the REN for the line. Each phone should have a sticker on it somewhere with the REN (Ringer Equivalence Number) for that phone listed. Add the numbers up to get a total applied REN. Most circuits have a max REN of 5. If your three phones REN exceeds that, or whatever the actual circuit REN is, you'll have the problem you're having.

Last edited by JBean3329; 03/27/19 11:16 PM.

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#628582 - 03/28/19 04:08 AM Re: Low Loop Current - POTS - AT&T/BellSouth [Re: JBean3329]  
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tenex Offline
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tenex  Offline
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New York
Thanks for the reply. Talk volume is low, and ring voltage is also low. These are REN 1 phones, WECO 500 and 2500. Not particularly exotic, and the loop should support at least 5 without them having a half-ring, correct?

At the same time, 35 V DC on-hook is pretty out of spec, wouldn't you say? Particularly at 4400' from a RT.

#628588 - 03/28/19 03:27 PM Re: Low Loop Current - POTS - AT&T/BellSouth [Re: tenex]  
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Posts: 19
tenex Offline
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tenex  Offline
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Joined: Apr 2008
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New York
I just re-tested the line, unloaded, and see 54 Vrms AC during ringing. That's way too low for spec.

#628598 - 03/28/19 07:58 PM Re: Low Loop Current - POTS - AT&T/BellSouth [Re: tenex]  
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Touch Tone Tommy Offline
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#628628 - 03/29/19 02:25 PM Re: Low Loop Current - POTS - AT&T/BellSouth [Re: Touch Tone Tommy]  
Joined: Apr 2008
Posts: 19
tenex Offline
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tenex  Offline
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Joined: Apr 2008
Posts: 19
New York
The ring booster would've been a solution on the low ring voltage, but the on-hook/off-hook current was still so weak that I could barely hear or be heard.

They actually sent a digital loop guy yesterday, since no one else was available. He checked the ringing plant and the card at the RT. He swapped-out the line card, and suddenly I was getting hit with a solid 93 Vrms AC.

Current is higher, as is on-hook voltage. Still not 25 mA or 47 V, but it's an improvement. They're looking at the RT now to determine why its talk battery output is so low.

Anyway, we're ringing loud enough to wake the dead again on 4 WECO 500s and 1 WECO 2500, so I'm happy.

#628631 - 03/29/19 03:38 PM Re: Low Loop Current - POTS - AT&T/BellSouth [Re: tenex]  
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justbill Online content
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Sandman also has the loop current regulators here that were in TTT's link. I use the ones with the automatic regulation that way if things change I don't have to go back, I've never had to replace one and they work as advertised.


Retired phone dude

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