# Something I don't understand about AC electricity **URL:** \ **Category:** Factual Questions\ **Created:** [December 19, 2011, 6:39pm UTC](https://boards.straightdope.com/t/something-i-dont-understand-about-ac-electricity/606760 "2011-12-19T18:39:13Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [December 23, 2011, 2:00am UTC](https://boards.straightdope.com/t/something-i-dont-understand-about-ac-electricity/606760/21 "2011-12-23T02:00:17Z")
> [@johnpost](#): > > old devices (before polarized or grounded plugs) might use the chassis as a part of the circuit. if plugged in so the chassis was hot then there could be a shock hazard. the chassis should be isolated from being touched but that depended on cardboard/paper/wood/rubber/plastic spacers/backing/knobs to be functioning; these would deteriorate or be lost and the device be a hazard to people who didn’t know that technology. > [@Leo\_Bloom](#): > > 1. When I was a kid (read: impulsive asshole) the call button of an elevator was missing, and I poked my finger in. IIRC, I was thrown a foot backwards and my arm felt like a safe had dropped on it. > > Is this the type of situation you’re talking about? > > 1. This was mentioned briefly upthread. Like most people here, I’ve accumulated a trove of transformers (?) for computer speakers, printers, and other doo-dads. They’re lying around in archaeological layers, and each says “must be used with x company”–they don’t even say which device, to add more spice to the mix-'n-match game. > > Is such 1-1 matching of electrical device to peripheral valid? > > I apologize for the hijack in question 2). 1. the situation i mentioned was different, accidental. you put your finger where it didn’t belong and you touched a contact/wire at a high voltage (high enough to cause a painful shock). 2)those power transformers might be used on other devices if done correctly. you need to match the voltage and current provided, the polarity and plug type. do it incorrectly and you might wreck your electronic device. ---
**Author:** ![Mdcastle](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Mdcastle](https://boards.straightdope.com/u/Mdcastle)\ **Post date:** [December 24, 2011, 12:58am UTC](https://boards.straightdope.com/t/something-i-dont-understand-about-ac-electricity/606760/22 "2011-12-24T00:58:01Z")
In countries where polarity isn’t enforced like those the use Schuko or Italian plugs, how do you safely replace a bulb in a table lamp since there’s a 50% chance of the shell being hot? I assume both lines are switched and you make sure a lamp is switched off before changing the bulb? Or are you just really careful? ---
**Author:** ![Silophant](https://avatars.discourse-cdn.com/v4/letter/s/a698b9/32.png) [@Silophant](https://boards.straightdope.com/u/Silophant)\ **Post date:** [December 24, 2011, 7:19am UTC](https://boards.straightdope.com/t/something-i-dont-understand-about-ac-electricity/606760/23 "2011-12-24T07:19:08Z")
What do you mean by shell? If you mean the body of the lamp fixture itself, that shouldn’t be part of the circuit in a sanely designed, non-malfunctioning lamp. As far as the bulb goes, glass is an insulator, so even if the polarity is reversed, the only part of the bulb that will be hot is the metal threading at the base. So you have to be careful not to touch the metal base until the bulb is all the way out of the socket. Or, since it’s a table lamp, just unplug it before you change the bulb. That’s probably the safest course of action. [Previous page](https://boards.straightdope.com/t/something-i-dont-understand-about-ac-electricity/606760.md?page=1)