Telephone Socket Change

[JOHNBOY42]

Bt only used a earth at a residental prems when it was the old party line.....now the earth is suuplied from the telephone exchange...one wire carries the voltage and the other the earth

 

[securityinstaller]

No they dont "normally" as most houses use double insulated telephone sockets. If you had a house and wanted a "metal" payphone then they WOULD do.
All I am stating is the regs which even most electrical contractors do not abide to when changing to metal telephone points.
Most that are designed for home use though are double insulated.
The relevant I was trying to make that was by "appearance the telephone sockets do not "appear" to be UK compliant.
(BSEN 6701) Is the standard

 

[Infidel]

Well I'll chip in here, no line ever supplied by BT needed to be earthed at the household apart from shared service, now defunct and It had it own separate earth provided by a spike in the garden.
The exchange fusing is a gas discharge fuse to stop anything nasty like 240 volts/lightening strikes coming back up the line and damaging the equipment,you also have one in the nte5 to stop anything nasty coming your way(but don't rely on it ).
50 volts dc is the normal operating voltage and if you short out this people ringing you will just get busy tone (thats how a phone works ).
75 volts ac is the ringing voltage to power the ringer(goes back to the old bell system hence the need for the capacitor in the nte )
Now perhaps what security was alluding to was bonding of the metal face plate to the to the metal of the back box, which unlikely to be earthed as it's only a phone point.

 

[JohnD]

Thats because BT take the earth from the house main earthing terminal!

Where do you get this rubbish from?

 

[bernardgreen]

Thats because BT take the earth from the house main earthing terminal!

That is the last place they would take it due to the amount of mains hum it could put into the phone system.

Even for the lightning protection that was once installed on lines at the subscriber's premises GPO used a ground rod.

Earthing a metal faced telephone socket to the electrical earth of the premises could by capacitive effect introduce a noticable amount of mains hum onto the phone circuit. The same applies to a metal back box behind a telephone socket.

 

[simonpolly]

You can buy stainless master sockets with a capacitor(line test looks for this or line will appear disconnected at eu (end user).No chance of blowing any fuses in the exchange i have never seen this happen,if incoming a or b lines touch a good earth then you will create a earth fault.some long lines e.g over about 5 km from exchange and fed by aerial cable that are likely to be struck by lightening still have earth protection built in at various positions but not at eu anymore.Also b.t openreach would not send an engineer out if the random robot tests did not see a master socket on the end of your line ,the robot generally looks for battery(voltage from another line) or earth contact faults.P.S SOME PLACES STILL USE EARTH CALLING,NO DIAL TONE WILL BE PRESENT UNTILL THE LINE IS EARTHED OUT,NOT A PARTY LINE.

 

[Infidel]

P.S SOME PLACES STILL USE EARTH CALLING,NO DIAL TONE WILL BE PRESENT UNTILL THE LINE IS EARTHED OUT,NOT A PARTY LINE

Yes but not in a single line installation in a house,they are all loop calling.
Earth calling lines are usually used on multiple line pabx's for offices. The earth for these was never bonded to the electrical earth and was provided by a deep driven earth spike. As said before don't bond anything to the electrical earth as it induces hum.The salt tester(subs automatic line tester) will test each leg for battery, earth, and low ir between the pair and look for the master socket resister and capacitor.I believe the new testers can tell the distance from the exch where the fault is pcp jb or o/h (no knackered 9083 with crappy leads) ahh the good old sodding wet and miserable days.