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#152516 05/25/05 03:05 PM
Joined: Oct 2000
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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).]

#152517 05/25/05 03:26 PM
Joined: Feb 2005
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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
Joined: May 2005
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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
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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
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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
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Snap! [Linked Image]

#152522 05/28/05 06:38 PM
Joined: Mar 2005
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Or the French knife switch, posted in PFD.
Alan


Wood work but can't!

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