# What is this? Fuse, insulator, or what? **URL:** \ **Category:** Factual Questions\ **Created:** [January 14, 2005, 5:24pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738 "2005-01-14T17:24:36Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![minor7flat5](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/minor7flat5/32/258_2.png) [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)\ **Post date:** [January 14, 2005, 5:24pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/1 "2005-01-14T17:24:36Z")
The other night something blew up on the utility pole outside my bedroom window (I started another [thread](http://boards.straightdope.com/sdmb/showthread.php?t=296657) about that). Yesterday, I collected the bits and pieces that I found on the lawn. [Electrical Bits](http://img.photobucket.com/albums/v186/minor7flat5/electrical-bits.jpg) My first thought is “insulator”, but that big lump of carbon is puzzling to me. Why would an insulator have metal contacts on the ends and a big lump of carbon inside. It appears that the carbon fits inside, but it could have come from somewhere else on the pole. ---
**Author:** ![TwoTrouts](https://avatars.discourse-cdn.com/v4/letter/t/a9adbd/32.png) [@TwoTrouts](https://boards.straightdope.com/u/TwoTrouts)\ **Post date:** [January 14, 2005, 5:34pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/2 "2005-01-14T17:34:31Z")
It’s a ceramic insulator. [This page](http://www.lappinsulator.com/lappgmbh/ceramic.asp) has a schematic breakdown of one type. Unfortunately, I do not know what the fill material is and its function. Maybe another more knowledgable doper will be along to explain. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [January 14, 2005, 5:52pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/3 "2005-01-14T17:52:46Z")
The vote here at the ol power co is we’re looking at pieces of a lightning arrestor used on distribution poles. The idea is that it acts like an insulator for distribution voltages (12,000 volts) but the carbon filling will form a path for high voltages (lightning) to “bleed” out of the system. It “should” have bled the current surge from the high voltage out and then resumed its job but sometimes the current is so strong that it destroys the arrestor. Think of it like a spillway on a dam. It is built in such a way that the water is held back, but too much water and it lets it out. It then goes back to normal levels. Overstress a spillway though and it could breach the dam. My guess is that either lightning struck the line somewhere close by or wind,ice, snow caused a high voltage transmission line (69,000 - 500,000volts) to come into contact with the distribution line. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 14, 2005, 6:12pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/4 "2005-01-14T18:12:01Z")
> [@BubbaDog](#): > > The vote here at the ol power co is we’re looking at pieces of a lightning arrestor used on distribution poles. That was my guess as well. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [January 14, 2005, 7:01pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/5 "2005-01-14T19:01:51Z")
> [@Q.E.D.](#): > > That was my guess as well. We actually talked it over. In our office are a number of engineers. The “review panel” was two control engineers and a power plant engineer. All of us thought the pieces looked like an insulator (the ceramic wavy parts) but the carbon core indicated a lightning arrestor (which has insulator looking parts). Again, it looked familiar but no one of us is a true “distribution engineer”. The distribution engineers are in another building, dress even funnier than we do, and would have been happy to provide us with long explanations and pages of pictures and diagrams had we been foolish enough to ask. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 14, 2005, 7:13pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/6 "2005-01-14T19:13:56Z")
> [@BubbaDog](#): > > All of us thought the pieces looked like an insulator (the ceramic wavy parts) but the carbon core indicated a lightning arrestor (which has insulator looking parts). I’m consulting my copy of the _Electrical Engineer’s Reference Book_, which thoroughly covers power distribution engineering. Its description of a surge arrestor closely matches the device in the OP: > [@Electrical Engineer's Reference Book](#): > > _Surge arrestor_… The modern device comprises an assembly of gaps and non-linear resistors in series, the whole being contained in a cylindrical porcelain housing. The use of multiple gaps gives the most rapid breakdown. The resistor elements offer a low resistance to surge currents (limiting the voltage across the arrestor) and a much higher resistance to the power-frequency follow current. Careful gap design ensures that the follow current does not restrike. ---
**Author:** ![minor7flat5](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/minor7flat5/32/258_2.png) [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)\ **Post date:** [January 14, 2005, 7:33pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/7 "2005-01-14T19:33:47Z")
You guys are the best! Now I can toss the whole works in the trash. My wife said nothing when I brought it in the house in a plastic grocery sack, but her look spoke volumes. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [January 14, 2005, 7:39pm UTC](https://boards.straightdope.com/t/what-is-this-fuse-insulator-or-what/284738/8 "2005-01-14T19:39:26Z")
> [@Q.E.D.](#): > > …I’m consulting my copy of the _Electrical Engineer’s Reference Book_, Well, if yer gonna cheat and actually look it up in a book. :dubious: 😛