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Author Topic: Short circuit telephone pair  (Read 10722 times)

digitalnemesis

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Short circuit telephone pair
« on: August 12, 2016, 03:00:30 PM »

What would happen if you short circuit a telephone line for a few seconds?

Reason I ask is I accidentally short circuited a phone jack (saw sparks) and this someone cured my HR fault.  :lol: (SNRM no longer drops when phone is off the hook)
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Weaver

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Re: Short circuit telephone pair
« Reply #1 on: August 12, 2016, 03:07:31 PM »

I've accidentally done this. No one came round to arrest me. I'm assuming that there's current limiting in the exchange or in the cab, some sort of short-circuit protection.

Faults of this ilk happen all the time, I believe. Last spring I had a couple of faults - nothing to do with _me_ - which were possibly of this type in the line and in the exchange hardware.
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Black Sheep

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Re: Short circuit telephone pair
« Reply #2 on: August 12, 2016, 03:16:49 PM »

What would happen if you short circuit a telephone line for a few seconds?

Reason I ask is I accidentally short circuited a phone jack (saw sparks) and this someone cured my HR fault.  :lol: (SNRM no longer drops when phone is off the hook)

All a short-circuit will achieve is to present an engaged tone to anybody ringing your landline number ............. nothing more. Can't explain how this would 'cure' a HR. 
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digitalnemesis

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Re: Short circuit telephone pair
« Reply #3 on: August 12, 2016, 03:23:14 PM »

All a short-circuit will achieve is to present an engaged tone to anybody ringing your landline number ............. nothing more. Can't explain how this would 'cure' a HR.

Isn't a short circuit similar to applying a wetting current? Perhaps this sudden extra flow of electricity is enough to 'burn' through the oxidation on bad joints?
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Weaver

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Re: Short circuit telephone pair
« Reply #4 on: August 12, 2016, 03:33:18 PM »

A wetting current doesn't necessarily _fix_ a problem for good. It may merely move things out of the most non-linear region, away from the origin (zero volts, zero amps).
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4candles

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Re: Short circuit telephone pair
« Reply #5 on: August 12, 2016, 03:37:52 PM »

Isn't a short circuit similar to applying a wetting current?

Only as much as using the phone.

Line current is limited, such that whether you're using the phone in your house, or you put a short on at the exchange frame, it's 40mA.

If you've got a milliammeter - try it and see.
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licquorice

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Re: Short circuit telephone pair
« Reply #6 on: August 12, 2016, 03:42:09 PM »

I very much doubt sparks were seen.
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digitalnemesis

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Re: Short circuit telephone pair
« Reply #7 on: August 12, 2016, 03:46:35 PM »

I very much doubt sparks were seen.

I saw it with my own eyes, poked a telephone jack (test socket) with a screwdriver and saw sparks.

Can record a video if you want proof but I don't really want to try that again.
« Last Edit: August 12, 2016, 03:48:58 PM by digitalnemesis »
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Weaver

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Re: Short circuit telephone pair
« Reply #8 on: August 12, 2016, 03:50:34 PM »

I can personally confirm that you can get sparks. ;D
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Black Sheep

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Re: Short circuit telephone pair
« Reply #9 on: August 12, 2016, 03:59:18 PM »

You can actually ....... not as big as throwing a spanner across a 6" solid copper bus-bar ........ but likkle-ikkle sparks.
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licquorice

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Re: Short circuit telephone pair
« Reply #10 on: August 12, 2016, 04:04:42 PM »

I guess if you're right on top of the exchange. There's not a lot of electric left by the time you get to my house!! ;D ;D
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digitalnemesis

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Re: Short circuit telephone pair
« Reply #11 on: August 12, 2016, 05:01:14 PM »

I guess if you're right on top of the exchange. There's not a lot of electric left by the time you get to my house!! ;D ;D

My cab is ~650m away whereas my nearest exchange is ~2km away.  :lol:
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burakkucat

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Re: Short circuit telephone pair
« Reply #12 on: August 12, 2016, 07:17:46 PM »

Quite a while ago, I recall discussing with 4C the maximum current that could be drawn on a telephony circuit. As I have forgotten the result I then obtained, the experiment was repeated --

[attachment deleted by admin]
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digitalnemesis

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Re: Short circuit telephone pair
« Reply #13 on: August 13, 2016, 07:38:14 PM »

Quite a while ago, I recall discussing with 4C the maximum current that could be drawn on a telephony circuit. As I have forgotten the result I then obtained, the experiment was repeated --

Where did you source the cable which plugs into the BT socket?
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burakkucat

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Re: Short circuit telephone pair
« Reply #14 on: August 14, 2016, 12:21:57 AM »

It's a MA1/631A test adaptor (also known as an Adaptor Test 3A) [1] and I believe I purchased it from JMW Limited along with a MA2/RJ45 test adaptor plus one other adaptor. The manufacturer's name is Chesivale Electronics [3] and a Google search may help.

Attached, below, are images of the three purchased and one home-made adaptor, along with part of a data sheet.

[1] http://www.telecomsupplyline.com/catalogue/testeq.htm
[2] http://www.jmwlimited.co.uk/Telecom_I_S.html?d=llinesman
[3] http://cpc.farnell.com/webapp/wcs/stores/servlet/Search?sf=&catalogId=15002&showResults=true&mf=101321&langId=69&storeId=10180
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