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Old 8th Dec 2017, 9:00 pm   #1
Ed_Dinning
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Default Earthing of phone lines

Hi folks, a pal of mine who has a large house and an annex that is separately occupied had one of his tenants complaining about a very noisy phone line.
Phone man called and diagnoses a faulty earth connection which he renews with a new earth rod.
He then tells my pal that he needs to get his electrical installation checked out as there are "earth leakage currents".

This is an old house from about 1800, but is wired to at least 16th edition standards with earth leakage trips on the DB's, non of which suffer from nuisance tripping. I have noted that the pipework cross bonding is not up to 17th edition standards.

I did not think that modern phone needed an earth wire, so was he being fed some bull by this linesman?

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Old 8th Dec 2017, 9:22 pm   #2
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Default Re: Earthing of phone lines

Telephones didn't need an earth connection (as I understand) unless they were party lines. But one leg of the incoming line pair is at or about earth potential (there may be about four volts difference WRT the other leg between the line and earth) and so the incoming pair is unbalanced with respect to earth.

But if both wires of the incoming pair are not directly connected to earth (which they shouldn't be) and the telephone is hummy, there is likely to be a problem elsewhere.

Do any of the telephone sockets have a metal backbox that is connected to the house electrical earth?
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Old 8th Dec 2017, 9:29 pm   #3
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Default Re: Earthing of phone lines

The only other time I've seen an earth connection (forgot to say earlier) is when a bakelite lightning arrestor was fitted, but these have long been superseded. I've seen tele lines with an earth connection at a distribution frame with a centre-tapped gas-gap, but never in a domestic installation: only on hilltop radio sites.

What incoming telephonic connecting hardware is at your pal's house?
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Old 8th Dec 2017, 9:36 pm   #4
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Default Re: Earthing of phone lines

Could be there is still an earth there from earlier days - shared service or the more recent Subs Private Metering (now both withdrawn). The BT SIN for a basic analogue DEL (Direct Exchange Line) does mention 'a local earth when required' See http://www.sinet.bt.com/sinet/SINs/pdf/351v4p8.pdf

Sadly not all BT engineers are well informed. When I had a PSTN socket first fitted, the guy didn't know where to put the earth wire - I had the Subs Private Meter facility which I'd had fitted to stop being made a 'shared service' line many years before - a little known 'dodge' ! In more recent years, I ended up clearing a noise fault which BT engineers couldn't find in a fires station in North Wales - so I got called ! Wasn't too hard to find the bad joint.
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Old 8th Dec 2017, 9:41 pm   #5
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Default Re: Earthing of phone lines

UK POTS phones are 'floating' and don't depend on an earth connection.

[Earth *was* necessary on the old 'party-line' setups where one side of the subscriber-pair was used against local earth to support each of the two party-line members]

If you pop the faceplate off the NTE5 and plug a phone into the socket thus revealed - and still have hum/noise issues then you should call your voice-phone-service provider [not necessarily BT - remember we've had Local Loop Unbundling for well over a decade] and complain.

Let the provider argue with BT/OpenReach: that's what you pay them for.
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Old 8th Dec 2017, 9:46 pm   #6
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Default Re: Earthing of phone lines

Quote:
Originally Posted by Pellseinydd View Post
The BT SIN for a basic analogue DEL (Direct Exchange Line) does mention 'a local earth when required' See http://www.sinet.bt.com/sinet/SINs/pdf/351v4p8.pdf
Ian,

With reference to the following excerpt of the SIN: 'There may not be a through metallic path from the BT network interface to the exchange so that the “battery” and “earth” at the exchange cannot be assumed to be repeated at the BT network interface.'..

When might this be the case? Are BT suggesting there may be a deliberate break? And were telephones ever connected to subs' premises by a single wire earth return? I ask this because of all the old insulator brackets on 'J's I see in passing, amongst them are the the odd single insulators, particularly in rural areas.
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Old 9th Dec 2017, 11:56 am   #7
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Default Re: Earthing of phone lines

Hi Gents, thanks for the details. House was run on a new 4(?)pair overhead a few years ago . A least one service appears OK, one other suffers more in windy conditions.

Apparently the linesman was connecting an earth lead on his test set to radiators and pronouncing "leakage currents!!!!

My simple line powered 20 year old Betacom house phone worked OK on both the outer and inner master socket connections (new master socket about 4 years ago).

Wireless router right next to phone, so suggested they try moving phone.

Ed


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Old 9th Dec 2017, 1:30 pm   #8
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Default Re: Earthing of phone lines

I may be wrong but were all lines earthed years ago?
I remember the 3 twisted bare copper cables coming through the lavatory overflow pipes to be connected around the cold water pipes with an expanding brass 2 screw clamp.
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Old 9th Dec 2017, 1:59 pm   #9
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Default Re: Earthing of phone lines

Hi Sam, that sounds like a mains earth, telecom was much thinner. The 2 wires (A&B) were not normally earthed, only momentarily by the party line select button. See details above.

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Old 9th Dec 2017, 2:18 pm   #10
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Default Re: Earthing of phone lines

No, they were taken into the incoming joint box or even onto the insulator on the wall bracket. From memory the wire was 3/029 copper, loose twisted and usually cleated to the mortar joints outside with lead headed cleats.
I assume that the GPO used the overflow pipe as an easy access as the water pipe was the other side of the cistern.
Ripped out loads in the old days when replacing lavatory cisterns, never reconnected one.
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Old 9th Dec 2017, 2:28 pm   #11
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Default Re: Earthing of phone lines

The was a time when it was normal to fit an earth consisting of uninsulated stranded copper wire connected to an earth spike. It was used in conjunction with lightning protectors fitted in the customers premises. It was also useful if the line was later converted to shared service.

Later (in the 1960's I think) protection was moved to the pole top and only fitted on lines with more than four spans of overhead wire.
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Old 9th Dec 2017, 3:07 pm   #12
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Default Re: Earthing of phone lines

Re windy conditions. Our line was noisy a year or so back and traced to the cable being worn through by 20+ years of rubbing against the neighbour's tree as it grew up, so to speak. Luckily for us it was his tree as it meant the fault wasn't on our property so we didn't have to pay.

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Old 9th Dec 2017, 3:18 pm   #13
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Default Re: Earthing of phone lines

If one leg of the incoming line becomes leaky to earth for any reason then this can cause hum on the line. If a fault becomes worse when windy or during damp conditions then this is likely to be the provider's problem. I would try and connect to the master socket and disconnect all other extension wiring and if the line still has a hum/noise on it bounce it back at the provider. If this cures the problem then maybe you have damp in a LJU or connection box somewhere inside the premises. Some PABX systems require a functional earth for call forwarding etc. but that is old now. A telephone line doesn't require an earth to operate as it works on a loop across the A and B legs. Some of our external "yellow" phones have an earth but this is to reduce lightning damage and simply earths the centre of a gas tube protector between the incoming legs.
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Last edited by Biggles; 9th Dec 2017 at 3:25 pm. Reason: typo/extra info
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Old 9th Dec 2017, 3:41 pm   #14
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Default Re: Earthing of phone lines

Problem with the line?
OH- It used to be a problem in the days of shared service/ extensions on plan sets (particularly the 10x with external extensions) and small PMBX, with ringing & system using an earth connection.
Other problems came about with SS and local mains leakage, where the bell would ring/ tinckle.
Poor earth - for lightning protection -a good earth was a MUST. I've seen plansets fried in Glencoe after a lightning storm, and 140 LB OH wire melted in Africa after a hit. As a TTA I visited a home in Strontian where the line protection had been thrown across the room after a hit. I've sat in Kinlochleven exchange in a storm and watched the frame light up.
BUT on modern home installations, I suspect lineman has had been eating a bad beef burger, with more of the bull output in it.
Unless the house has a phone system, where the earth system needs to comply with standards.
Phone system- decent earth system needed.
Simple phone lineman is talking out of part of trousers, that is best covered up.
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Old 9th Dec 2017, 4:01 pm   #15
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Default Re: Earthing of phone lines

While tracing a fault a couple of years ago, an Openreach engineer requested a mains earth (extension lead), into which he plugged an instrument which, I believe, detected the distance to a leaky connection box on a nearby pole, suggesting that the line wasn't intentionally earthed.
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Old 9th Dec 2017, 5:20 pm   #16
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Default Re: Earthing of phone lines

A TDR will not always show up one leg leaky to earth. It's possible that the linesman was trying to use the earth connection as one side of the TDR to show that fault up. Most times I need an "earth" I normally just poke a large screwdriver into the soil and croc onto that. This would be used with the 109 to track U/G cable routes. I don't think I have ever used a mains earth for line testing. I would think you are asking for problems doing that. I did make a pocket gadget for injecting line voltage into a disconnected pair to check for current taken to indicate leakage across the pair and also between each leg and earth. This is quite a useful tool for finding good and poor pairs on an underground cable.
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Old 31st Dec 2017, 1:47 am   #17
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Default Re: Earthing of phone lines

Using nearby pipes to get an earth for your tester is an old dodge( I use it all the time) if no mains socket or other bonding point is handy. If the radiator is not earthed( for instance fed by plastic pipes somewhere) then it should be possible to tell from the readings on your tester. If I was at all suspicious then I would simply nip out to the van and use my mains extension lead Nd test plug to obtain a good earth.
There have been a few occasions were the mains socket I was using was actually reversed or not earthed.
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Old 31st Dec 2017, 11:30 am   #18
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Default Re: Earthing of phone lines

I had some problems in 2012, I measured a lot, got help on another forum, and the sent the telco a full report of my measuring, (scheme/thread here: classicrotaryphones.com/forum/index.php?topic=8228.msg89542#msg89542)
They did not argue, they dug in to the snow and located the fault as I concluded in the mail (by help from the forum) and fixed the fault.

No problems!


Why did I do that? many years earlier (before cell-phones), I suddenly just had one way connection, I could here the other party, they could not hear me. I tested by swapping telephones with my neighbor, but nothing changed, so I called from my neighbor and reported the error, and the refused. Nothing is wrong! it has to be your phone.

My solution was to supply back with mains connected to the phone line, then they got something wrong at the exchange, and suddenly my phone worked OK again. (heard nothing from the telco)

This is not funny way to solve it, but the only I had at that time.

dsk
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Old 31st Dec 2017, 12:33 pm   #19
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Default Re: Earthing of phone lines

It would be interesting if your method of getting the company's attention/ cooperation was in more general use dsk: Boaters Sam's description of the earthing set up [post 10*] matches the redundant wiring I found in the front garden here in Bexhill. I'd always known that earth wires might be deployed in telephone installations from my employemt [as a clerk] in the GPO circa 1968 but I was intrigued to read the technical background here.

Dave W
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Old 31st Dec 2017, 2:06 pm   #20
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Default Re: Earthing of phone lines

As others have said the GPO earth is no longer required for normal PSTN lines. I thing they were most commonly used for party lines and SPM. I come across them occasionally and I think they went to an earth plate about 6-8" square in the ground. We (Openreach) still use earth for testing( it never goes faulty!) as a reference.
I heard stories that some people could get faults on party lines in really dry weather. The cure was a watering can!
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