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#152516 - 05/25/05 03:05 PM What is This?  
Admin  Offline

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Joined: Oct 2000
Posts: 3,439
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
Instructor
NECA/IBEW Electrical Training Center
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[This message has been edited by Webmaster (edited 05-25-2005).]


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#152517 - 05/25/05 03:26 PM Re: What is This?  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
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.


Larry Fine
Fine Electric Co.
fineelectricco.com

#152518 - 05/28/05 04:11 PM Re: What is This?  
techie  Offline
Member
Joined: May 2005
Posts: 246
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?


#152519 - 05/28/05 04:31 PM Re: What is This?  
NJwirenut  Offline
Member
Joined: Sep 2001
Posts: 806
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.


#152520 - 05/28/05 04:32 PM Re: What is This?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
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.


#152521 - 05/28/05 04:32 PM Re: What is This?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Snap! [Linked Image]


#152522 - 05/28/05 06:38 PM Re: What is This?  
Alan Belson  Offline
Member
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
Or the French knife switch, posted in PFD.
Alan


Wood work but can't!


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