daisychain POTS phone wiring and DSL filters?

Al Dykes wrote in part:

Yes, although the phones may draw too much current for a single filter. You are better off with a purpose-made splitter.

The daisy-chaining harms nothing downstream of the filter.

-- Robert

can you give me a make/model or a URL for a POE DSL/POTS device?

Since the central office lines are current limited, I don't think you'd even come near burning out any filter. Much less having more than 2 or 3 phones off hook at the same time.

I'd tend to agree, but I wouldn't be so sure about ringing current. There is nothing stopping those filters being made very cheaply, although I suspect there not much more than a simple low-pass filter. There may be a resistor on the thru leg that could fry.

-- Robert

The FCC specs out one ringer load not to exceed 12 mA of current and the phone company's central office is supposed to support up to five ringers (5 REN). So that's only 60mA at 2 seconds on and 4 seconds off with five phones ringing. If you add more phones and draw too much current, the C.O. will see it as an off-hook condition and the D.C. line current is limited to 20-40 mA.

DecaturTxCowboy wrote in part:

Thanks for the specs!

But crunch it through: 60 mA @ 90VAC is 5.4W. Maybe 4.0 if it's 90 Vp-p. Still plenty to blow a 1/8W resistor, depending on exactly how much drop it takes.

The resistor had better be below 35 ohms if it's going to handle a full house downstream iff the CO drives 60 mA.

I have a single DSL dongle filter in my hot little hand. It was graciously supplied by SBC when I got DSL. My DVOM rings it out as 46 ohm resistance on each leg through.

It might well blow on a full-house load if it only has

1/8W resistors inside it's sealed little body. If the CO drivers are constant-current, it'll fry. If it's 90VAC constant-voltage, the extra 92ohms will only drop current from 60 to 56 mA and it'll still fry. Of course, it might not fry if my phones draw less ring current (probable).

-- Robert

Long long time ago, the central office line cards used "ballast lamps", one each in series with the tip and ring leads to limit the current. Just as in a regular light bulb with a tungsten filament that has an inverse conductivity to temperature coefficient, the more current drawn

- the hotter the filament got - and its resistance increased, thus "limiting" the current in the loop. But since it wasn't a linear curve, it almost looked like it was a true current limiting device, as opposed to a constant current device. Current technology uses a solid-state device.

Just a bit of history trivia....

My new bumper sticker - - -

********************************************

• I'd rather go hunting with Dick Cheney *

• than driving with Ted Kennedy *

********************************************

I have no idea where this "too much current" story came from. I've done the whole-house deal a half-dozen+ times. Does anyone have a filter damaged by such?

A) Are we talking ringing or talking current? Ring will be near zip, unless you have 7 sets all with honest-to-gosh WECO 2-clanger ringers. Modern tweedle-deedles are typ. rated at 0.1 REN anyhow.

Talk current is limited by the CO, and the loop length; with 4+ phones off hook, none will be happy, filter or not..

B) The real issue is connectors; you'll need a dual-receptacle plate and a short modular cord.

Anyway the resistance values on the filter are quite lod, so only a fraction of this power gets dissipated by them. The resistance valöues I have seen have been around 20 ohms per resistor or smaller.

Here are details of one ADSL filter I took apart to find information what is inside it:

In the end of this document you can find links to information on some other filter products.

The typical ADSL filter there is not just one resistor. There is typically some coils (with considerable resistance on them) and then the resistor. So not all the power gets disspated by this resistor.

If this rign current happens to be that 60 mA maximum (current limited on the central office), then in the circuit shown at

the power loss on each of those 20 resistors is

60 mA * 60 mA * 20 ohms = 0.072W

OK post