# Those chains hanging from school buses **URL:** \ **Category:** Factual Questions\ **Created:** [October 17, 2001, 1:20am UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868 "2001-10-17T01:20:31Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![TheeGrumpy](https://avatars.discourse-cdn.com/v4/letter/t/779978/32.png) [@TheeGrumpy](https://boards.straightdope.com/u/TheeGrumpy)\ **Post date:** [October 17, 2001, 8:48pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/21 "2001-10-17T20:48:26Z")
Since the chains I’ve seen on school buses don’t touch the ground (they hang several inches above), I tend to discount the electrical theory. And since they are, in fact, automatic tire chains, I’m inclined to believe the traction theory. That doesn’t mean that fuel trucks don’t use chains for grounding to avoid nasty sparks. ---
**Author:** ![Swede\_Hollow](https://avatars.discourse-cdn.com/v4/letter/s/3bc359/32.png) [@Swede\_Hollow](https://boards.straightdope.com/u/Swede_Hollow)\ **Post date:** [October 17, 2001, 10:34pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/22 "2001-10-17T22:34:17Z")
I’ve seen chains on trucks and buses (unlike some of the above, I see less now than I used to) and these were NOT the traction devices that are available. There were usually only one or two chains hanging down in the back of the vehicle. Some semi’s had them connected to the frame near the “fifth wheel” or whatever the connection device is called. A couple sites: > [@](#): > > Even today, gasoline trucks usually have a dangling wire or chain to drain off any charge that might spark and ignite their cargo. [http://www.gi.alaska.edu/ScienceForum/ASF7/717.html](http://www.gi.alaska.edu/ScienceForum/ASF7/717.html) and > [@](#): > > Subclass: 219 > Chain-type grounding means: > This subclass is indented under subclass 217. Subject matter wherein the electric charge is discharged from the vehicle by a flexible electroconductive chain-type member which is connected at one end to the vehicle and at the other end contacts a ground. > (1) Note. “Chain” in this subclass includes such devices as chains, cables, flexible rods with attached wheels, etc. [http://www.uspto.gov/web/offices/ac/ido/oeip/taf/def/361.htm](http://www.uspto.gov/web/offices/ac/ido/oeip/taf/def/361.htm) ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 18, 2001, 2:31am UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/23 "2001-10-18T02:31:07Z")
I don’t think it has anything to do with the earth’s magnetic filed. Instead (and this is a SWAG), I believe static build-up is the fault of three things: - Rubber tires - Airflow over the car (wind) - Dry air The **wind** creates a build up of static charge on the car when you’re driving. The **rubber tires** have extremely high resistance, and thus do not discharge the car to earth ground. **Dry air** keeps the electrons from bypassing the tires. Again, just a SWAG. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 18, 2001, 6:56am UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/24 "2001-10-18T06:56:07Z")
> [@](#): > > \*Originally posted by Crafter\_Man \* > **I don’t think it has anything to do with the earth’s magnetic filed.** You’re right about that. A loop of wire travelling through a magnetic field will, indeed, induce current on the loop. But a lump of metal travelling through a magnetic field does not build up static charge. Well, there will be a tiny amount of positive charge on one end of the lump and negative charge on the other, but it’s maintained by the movement and will disappear once the movement stops. ---
**Author:** ![madman1949](https://avatars.discourse-cdn.com/v4/letter/m/90db22/32.png) [@madman1949](https://boards.straightdope.com/u/madman1949)\ **Post date:** [October 31, 2013, 5:25pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/25 "2013-10-31T17:25:21Z")
The school buses in our district are all equipped with these chains. My nephew is a mechanic for the district and confirmed that these really are self deploying tractions devices. The chains are mounted to a wheel driven device that can be lowered with air pressure. A small rubber wheel is pushed against the inside of the rear inner tires of the bus. This causes it to spin and the chains that are attached to it are thrown one by one under the front of the tires. I have been seriously thinking about checking to see if I can have them installed on my motorhome. With the limited clearance and fiberglass body I would rather not run regular chains. The real beauty of these is that if a chain breaks it simply falls off and does no damage to the vehicle. Grounding straps on the other hand are single in design and hang from the body of the vehicle and not the axle. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [October 31, 2013, 5:39pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/26 "2013-10-31T17:39:00Z")
12 year old zombie thread, but still… [Here is a write-up on the Onspot automatic chain system.](http://www.onspot.com/indhisfr.htm) ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [October 31, 2013, 6:31pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/27 "2013-10-31T18:31:10Z")
Aircraft do build up major static electricity. They have static discharge wicks along trailing edges & other ways to keep it dissipated. Many have a stiff piece of small cable that will drag on the ground attached to the landing gear. I remember from years ago that almost all fuel tankers had chains for static discharge, then they went to stiff graphite straps. Also, there has been cases of people lighting off the fumes of refueling their cars because of undissipated or build up of static electricity from the fuel flowing through the hose. ---
**Author:** ![Whiskey\_Dickens](https://avatars.discourse-cdn.com/v4/letter/w/9fc348/32.png) [@Whiskey\_Dickens](https://boards.straightdope.com/u/Whiskey_Dickens)\ **Post date:** [October 31, 2013, 8:31pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/28 "2013-10-31T20:31:25Z")
> [@KCB615](#): > > \*\*(SNIP) \*\* The chains are self deploying tire chains, made by a company called OnSpot. **(SNIP)** There’s a much better description here: [http://www.onspot.com](http://www.onspot.com) Oldest ugly website ever? 12+ years old, and it doesn’t look a day over 18. Probably completely uncha(i)nged since 2001. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [October 31, 2013, 8:36pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/29 "2013-10-31T20:36:30Z")
website has no traction. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [October 31, 2013, 10:10pm UTC](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868/30 "2013-10-31T22:10:34Z")
Zombie thread about chains, … on Halloween. 😃 [Previous page](https://boards.straightdope.com/t/those-chains-hanging-from-school-buses/87868.md?page=1)