Whats this all about then

[oceansoul]

Not really DIY or domestic related this one; Whilst out on another site today, i found this strange set up in the corner of the room.

What starts out looking like a DNO lead sheathed supply cable....

Untitled

• oceansoul
• 4 Jun 2015
• 1

which comes from under ground, then terminates in an old (60s??) metal cutout, through some conduit, up to a box with ........ a BT telephone socket!!!!

Untitled

• oceansoul
• 4 Jun 2015
• 1

I carefully removed the BT socket faceplate, not sure what to expect behind only to find 4mm2 cables (i think thats the size. Possibly 6mm2?) into choc blocks then onto telephone cables!!

Untitled

• oceansoul
• 4 Jun 2015
• 1

Obvoulsy this is no longer the supply into this building, that is via "our own cable" in SWA from a nearby building. I guess it once was and somehow some one GPO/BT/Openreach, has tried to reuse the cores as a phone line!! I tried to trace the lead cable outside, but could see no sign of it in our ducts.

 

[deadshort]

Now if it had been a BT socket supplying the cut-out that would have been impressive



DS

 

[333rocky333]

With all this low power led stuff, bet its only a matter of time before someone uses there phone line for emergency lighting

 

[drgl]

& a split pair on the CW1308 Hope they don't have BB, that cable will be terrible for it!

 

[ban-all-sheds]

With all this low power led stuff, bet its only a matter of time before someone uses there phone line for emergency lighting

It's a high impedance supply - I suspect that with any meaningful amount of lighting (even LED) the voltage would collapse.

 

[Robin0577]

With all this low power led stuff, bet its only a matter of time before someone uses there phone line for emergency lighting

It's a high impedance supply - I suspect that with any meaningful amount of lighting (even LED) the voltage would collapse.

If I'm remembering my college maths correctly, a phone line will support a total load of about 3 to 4 watts, so not really a meaningful amount, even with LED, as you suggest.

 

[Taylortwocities]

The average UK line loop current is 35mA. It can be more or less, depending on the length of the copper loop. At that current and an exchange battery of 50VDC we are talking about the possibility of lighting up a LED of not more than about 2watts.

But your free light wouldn't last for long, I fear.

To light the Lamp, you will basically be placing a resistance across the line and the exchange will detect this as "off hook". In the good old Strowger/crossbar exchanges this state of grace could continue for quite a long time. However, modern exchanges will detect a permanent off hook condition and will then auto test the line.

This will probably be followed by a visit from the OpenReach man and a fine for contravening your contract with BT.

 

[333rocky333]

oh, never realised that.
How do some garages have extension bells you can hear ring halfway up the road.

 

[Taylortwocities]

Because the extension bell (as well as the "bell" in the phone itself) is across the line in series with a capacitor.

AS you know, a cap is open circuit to DC so there is no DC loop. The ringing current is AC (well, more like a square wave).

One of the loop tests that can be done from the exchange is to check the bell/cap circuit buy doing an ohms test and then reversing the test leads, you'll then see the ringing cap charge and discharge.

 

[SimonH2]

It's possible that the cable happened to go somewhere convenient, and someone decided to reuse the cable for a data connection between two buildings.

 

[AndyPRK]

Well I don't think a BT engineer found the cable in the back of his van !

 

[dannyboi2003]

It's not an ex MOD site or previously connected with them by any chance?