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#152516 - 05/25/05 12:05 PM What is This?
Admin Offline

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Registered: 10/07/00
Posts: 3417
Loc: NY, USA
Quote:
I had a student bring this in to me today and I'd like to find out what it is. He found it in the attic of a house. The brass piece screws on to cover the part sticking up in the middle. I'm guessing a telegraph relay, but that's just a guess.

Laura Jenkins
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NECA/IBEW Electrical Training Center


[This message has been edited by Webmaster (edited 05-25-2005).]
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#152517 - 05/25/05 12:26 PM Re: What is This?
Larry Fine Offline
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Registered: 02/18/05
Posts: 693
Loc: Richmond, VA
This is a fused lightning arrestor for a telephone line. The cap covers a pair of carbon spark-gaps. The bottom terminal is for ground.
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#152518 - 05/28/05 01:11 PM Re: What is This?
techie Offline
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Registered: 05/17/05
Posts: 246
Loc: palo alto, ca usa
The two terminals labeled "L" are for the incoming telephone line, The two labeled "I" are for the telephone instrument, and the terminal labeled "G" is for ground.

Note that the terminal on the upper right is corroded, but none of the others are.
Can anybody explain why that particular terminal would be corroded, but not the opposite side?
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#152519 - 05/28/05 01:31 PM Re: What is This?
NJwirenut Offline
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Registered: 09/15/01
Posts: 806
Loc: Bergen County, NJ
Quote:
Can anybody explain why that particular terminal would be corroded, but not the opposite side?


That sort of thing is common when DC wiring gets wet. Electrolysis causes one terminal (the cathode, IIRC) to corrode very quickly, while the other electrode is hardly effected.
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#152520 - 05/28/05 01:32 PM Re: What is This?
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Remember that the telephone loop current is DC. That's the same sort of corrosion of one pole that you can see on an automotive battery terminal, or on other DC switching equipment.
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#152521 - 05/28/05 01:32 PM Re: What is This?
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Snap!
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#152522 - 05/28/05 03:38 PM Re: What is This?
Alan Belson Offline
Member
Registered: 03/23/05
Posts: 1803
Loc: Mayenne N. France
Or the French knife switch, posted in PFD.
Alan
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