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Old 30th Jan 2018, 5:18 pm   #41
broadgage
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Default Re: Earthing of phone lines

I believe that earth return was avoided because the return current would tend to pass along the railway lines rather than through the general mass of earth, and this might interfere with track circuits used for signalling purposes.

Sometimes the supply was derived from an isolating transformer, in other cases it was either phase and neutral or two phases from the public supply.
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Old 30th Jan 2018, 10:58 pm   #42
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Default Re: Earthing of phone lines

Single cut ( rail signal terminology = circuit where supply is broken in a relay with a contact in one, usually supply leg). Double cut places a relay contact on both legs.
Earthing on rail signaling circuits presents a fault, as, in single cut circuits, any earth fault on a signal wire could S/C the relay contact to break the circuit, causing a fault condition to misoperate a signal or equipment... Hence the introduction and preference for double cut circuits.
For those of us familiar with circuit diagrams of relay contacts- rail drawings are as speaking in a foreign tongue. ( From memory)Current system shows a relay operate path ( e.g.) as a straight line with a make contact depicted as a "v" above the line, and a break as an inverted v below the line. This was adopted to prevent mistakes as the older practice was to show make contacts as above but not connected to the line, but break contacts as above, but connected to the line. The newer practice was adopted after a lot of drawing office mistakes.
in parts of the country where traction current can be delivered over the tracks, signaling sections were ( I don't know if this is still the practice) isolated by using large inductors and AC signaling. Each rail was connected to the next length using a large inductor so that 50 Hz would pass, but the inductance blocked the HF signals.
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Old 31st Jan 2018, 1:21 am   #43
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Default Re: Earthing of phone lines

I did read somewhere that the reason why 3rd and 4th rail traction supply had to be used for London's District and Metropolitan Lines' electrification circa 1904 was due to the Post Office's concern about leakage currents affecting the telegraphs. The Post Office didn't seem to have been bothered by tube lines that had opened a decade or so earlier that used only third rail electrification, but I suppose that, unlike the District & Metropolitan railways, tube lines run in cast iron tunnels that would have provided effective shielding. The Central Line tunnels pass within a few hundred yards of what used to be the Post Office's central telegraph office near St. Pauls seemingly without causing problems, and the Central Line didn't change to 3rd and 4th rail system until the 1930's.
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Old 31st Jan 2018, 11:20 pm   #44
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Default Re: Earthing of phone lines

3rd rail is a rail close to a running rail and constantly powered at 650vDC. The fourth rail is a rail in the middle of the running rails ( referred to as the "four foot"). I've heard several tales of when this rail is live. But the consensus of opinion on all NR courses I've been on was to treat as live, as it depended on trains/UG in section.
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Old 31st Jan 2018, 11:43 pm   #45
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Default Re: Earthing of phone lines

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I've heard several tales of when this rail is live. But the consensus of opinion on all NR courses I've been on was to treat as live, as it depended on trains/UG in section.
Did I read that the two 'live' rails are at different potential WRT earth? Something like +400V to earth and -250V to earth giving 650V across them but asymmetrical to earth?

Something to do with protection perhaps? Sorry to veer off topic a tad.
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Old 1st Feb 2018, 12:56 am   #46
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Default Re: Earthing of phone lines

NO- third rail ( one adjacent to a running rail, but mounted on insulators) is live WRT earth at 650v DC. NR safety courses advised us to treat the fourth rail, mounted midway between running rails as live at all times at a hazardous voltage.
Something else public is not aware of is that on the likes of the West Coast mainline, there are things called "red bonds", where a high voltage can exist on earth. And the line voltage on overhead is constantly uprated using autotransformers to keep the Overhead at 25KV.
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Old 1st Feb 2018, 9:47 am   #47
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Default Re: Earthing of phone lines

Back on topic please.
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Old 1st Feb 2018, 10:30 am   #48
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Default Re: Earthing of phone lines

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Originally Posted by russell_w_b View Post
Quote:
Decades ago, the railway used to send mains voltage along telegraph routes as a cheap way of supplying mains to signal boxes etc.
The insulators used thus were meant to be red in colour instead of off white, and on multi circuit routes were so placed so as to minimise the chances of accidental contact.
I have one of those red insulators (ex-Settle and Carlisle rly). They were mounted on the furthest end of the top crossbar, and yes: they would support mains conductors as you describe.

But were they on an earth return system too? Or would there be live and return (possibly floating) conductors along the same run as telegraph ccts?
It wasn't only the railways that ran mains on overhead routes. I remember a short route with mains wires on insulators on a PO/BT route between the exchange and the post office about quarter of a mile away on the isle of Canna in the Inner Hebrides. The couple of phone lines were on arms lower down (can't find a photo) The generator was in a building by the 'Post Office' (an 8 x 10 wooden shed) which was run to supply the adjacent house. It also charged the batteries when running at the nearby 'exchange' in another 8ft x 10 ft shed (two of the four 12 volt batteries which supplied the exchange can be see bottom right in the photo) This was the situation until 1995 but the route was still in situ in 1997 by which time the exchange (remote concentrator) was in a new building about half a miles away, with a generator in an adjacent building.

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Old 1st Feb 2018, 3:46 pm   #49
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Default Re: Earthing of phone lines

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'It wasn't only the railways that ran mains on overhead routes. I remember a short route with mains wires on insulators on a PO/BT route between the exchange and the post office about quarter of a mile...'
Interesting stuff, Ian: thanks for that. Some nice 'light straw' equipment there. I guess in such a remote location it was expedient to carry the supply this way.

Incidentally, these telegraph earth-return circuits to the PO you mentioned earlier in post #37... Were they a straight-forward key/sounder system or did they use a 'silent' Fullerphone-type arrangement where signals could not be detected in the earth-loop (and so intercepted)?
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Old 1st Feb 2018, 8:18 pm   #50
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Default Re: Earthing of phone lines

Re the 'earth return' telegraph circuits - I'll have to some 'digging' through diagrams. Luckily I have an original set of diagrams for the GPO's telegraph and telephone equipment in use in circa 1886 - so that should give a clue.

I have one of those exchanges but mine came from a more remote location - https://www.google.co.uk/maps/place/...9!4d-2.0695406
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Old 1st Feb 2018, 8:36 pm   #51
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Default Re: Earthing of phone lines

If it's that age it won't be Fullergraph stuff as I believe that was invented in 1915 during WWI. I have a book: 'Instruction in Army Telegraphy and Telephony' (1914) and I imagine some of the circuits within will be like the ones you are about to look for.

The book mentions that earth returns and the advantages for telegraph ccts, but only on short telephone ccts, 'especially in the country, well away from other wires carrying electric currents; where they are often used for military work...'
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Old 1st Feb 2018, 10:58 pm   #52
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If it's that age it won't be Fullergraph stuff as I believe that was invented in 1915 during WWI. I have a book: 'Instruction in Army Telegraphy and Telephony' (1914) and I imagine some of the circuits within will be like the ones you are about to look for.

The book mentions that earth returns and the advantages for telegraph ccts, but only on short telephone ccts, 'especially in the country, well away from other wires carrying electric currents; where they are often used for military work...'
Ah! I know that book, worked in field telephone circuits when in uniform! I was a very young officer serving under a guy who went by the title of 'The Earl Kitchener of Khartoum' !! But that was a very very long time ago - seem to remember wear boots and spurs and carrying a big sword. Old field telephones working over field cable - sometimes using earth return - seem to remember earth spikes about 9 inches long with a brass terminal near the top. Happy days!
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Old 1st Feb 2018, 11:51 pm   #53
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Quote:
Originally Posted by Pellseinydd View Post
It wasn't only the railways that ran mains on overhead routes. I remember a short route with mains wires on insulators on a PO/BT route between the exchange and the post office about quarter of a mile away on the isle of Canna in the Inner Hebrides. The couple of phone lines were on arms lower down (can't find a photo) The generator was in a building by the 'Post Office' (an 8 x 10 wooden shed) which was run to supply the adjacent house. It also charged the batteries when running at the nearby 'exchange' in another 8ft x 10 ft shed (two of the four 12 volt batteries which supplied the exchange can be see bottom right in the photo) This was the situation until 1995 but the route was still in situ in 1997 by which time the exchange (remote concentrator) was in a new building about half a miles away, with a generator in an adjacent building.
The exchange, MK1, would have been a device concocted in Edinburgh, using cold cathodes. The MK2 device used SCR , and lower voltages. Mk1, had the disadvantage that it worked best when shielded from natural light. MK2 had problems with damp, prevalant in the isles. As for mains on overhead( GPO/ non GPO) , dropwire no 4 ( the realy heavy stuff) fed many a cow/chickenshed in the Argyll pensilula for many yerrs.
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Old 2nd Feb 2018, 1:40 am   #54
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Back on topic please.
Would it be permissible to start a new thread on old railway electrification systems ? Not domestic I know, but it IS vintage and electrical.
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Old 2nd Feb 2018, 9:43 am   #55
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Default Re: Earthing of phone lines

Sorry no. There are plenty of railway forums where you can discuss that subject.
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Old 2nd Feb 2018, 12:46 pm   #56
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The exchange, MK1, would have been a device concocted in Edinburgh, using cold cathodes. The MK2 device used SCR , and lower voltages. Mk1, had the disadvantage that it worked best when shielded from natural light. MK2 had problems with damp, prevalant in the isles. As for mains on overhead( GPO/ non GPO) , dropwire no 4 ( the realy heavy stuff) fed many a cow/chickenshed in the Argyll pensilula for many yerrs.
The exchanges you are referring to are the tiny 10 line semi-electronic exchanges introduced in the early 1970's. I remember seeing one, on display on an openday at Oban exchange in 1973. Because I showed 'unusual' interest in it, the TO explained that it was the' latest technology in exchange switching' and then he asked what I did for a living as I seemed to know a bit about telephones. I just said I was a senior commissioning engineer working on getting Birmingham Rectory - the first TXE4 - going. His jaw dropped.

One of the 10 line exchanges was used on Foula & Papa Stour (in the Shetland islands) plus Soay and other Inner Hebridean Islands before they were replaced with similar exchanges to the one on Canna. These were known a 20 line 'Island Automatic eXchange No 5' (IAX5). However Soay was never converted. I have the mainland end of the junctions from Canna, Muck, Rhum and Soay recovered from Mallaig in 1997. These exchanges were developed by Ian McPherson of THQ Scotland - the exchanges being built by PO Factories. Somewhere I have a folder of notes and diagrams that Ian McPherson wrote and had ended up at Inverness before coming my way. There is an article in the IPOEE Journal describing the 10 line exchange. The workings of the IAX5 appeared in the THG Journal around 2000.

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