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Bt Master Socket. |
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#1 |
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Forum Member
Join Date: Jul 2010
Posts: 24,096
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Bt Master Socket.
I've had some private messages, this is to clarify situation:
IF YOU CONNECT ANYTHING TO A TELEPHONE LINE, IT MUST BE AFTER THE BT MASTER SOCKET, WHICH MUST BE THERE ! ie, the 2 incomming telephone wires must go straight to pins 2,5 on a master socket, before "meeting" anything else! Any other devices across the line are after that. Main reason is, the master socket has an overvoltage protector. If "something nasty" accidentally gets on the line, the this stops anyone who "might be working on the line" from belng killed. And also protects the customer's line unit from damage, at the phone exchange. |
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#2 |
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Forum Member
Join Date: Jul 2003
Location: Felixstowe
Posts: 258
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Quote:
Main reason is, the master socket has an overvoltage protector. If "something nasty" accidentally gets on the line, the this stops anyone who "might be working on the line" from belng killed. And also protects the customer's line unit from damage, at the phone exchange.
The master socket also incorporates a capacitor and resistor in series across the two wires. Test equipment uses those when doing line tests. |
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#3 |
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Forum Member
Join Date: Jul 2010
Posts: 24,096
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Drivel ! Obviously, the protector CAN prevent people being killed, that's the main reason for it! Wasn't needed before we had phone sockets ...........
..... almost any fault that might be dangerous wd put mains on 1 leg only, not both! SInce mains phases are fixed w.r.t. ground - not floating - that's frigging lethal. Pray, what planet are you on ? |
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#4 |
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Forum Member
Join Date: Jul 2003
Location: Felixstowe
Posts: 258
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Quote:
Drivel ! Obviously, the protector CAN prevent people being killed, that's the main reason for it! Wasn't needed before we had phone sockets ...........
..... almost any fault that might be dangerous wd put mains on 1 leg only, not both! SInce mains phases are fixed w.r.t. ground - not floating - that's frigging lethal. Pray, what planet are you on ? 2. Despite much googling to find authoritative info on the over-voltage protection device I did not come across anything which said the main reason is to protect people from being killed. 3. And you are incorrect when you write "Wasn't needed before we had phone sockets ." You might find a read of http://www.britishtelephones.com/lightng.htm interesting. 4. I don't contend, I didn't say or even imply, that all or the majority or even a significant portion of faults producing dangerous voltages would put them on both legs. Even you wrote "almost any fault ..." which I interpret as you recognising that it is possible. 5. If you were a technician working on in-service lines every day, would you be confident of the "life protecting" properties of the over-voltage devices? |
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#5 |
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Forum Member
Join Date: Jul 2010
Posts: 24,096
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Phew!
1. lightening is attracted to conical earthed structures sticking up, eg church steeples. Where a lightning conductor provides an “easier path”. 2. Lightning does not often strike horizontal wires. Especially where their potential is fixed relative to ground (in this case, by the 50v battery system). It usually goes for pointy buildings because of charge induction on moist earth in surrounding area, and electrc field distortion at the point. 3. Fuses are no protection against electrocution. Just a very small current will kill. 4. I can;t remember fuse links in the old style junction boxes, but that’s irrelevant. 5. if mains voltage gets onto either leg, there’s nothing to stop it (except local RCB). However, linesmen normally use a cable tracer when working on wiring, and the 50 Hz would be obvious. Using the probe then tells you which cable, hence the subscriber. 6. the overvoltage protector only limits the voltage between the 2 wires, so at least you don’t get the full 240 (or even 415) volts across them. 7. common sense when working, ie rubber boots, don;t hold onto the metal cabinet , etc ........ |
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