# Amps and volts to watts: conversion **URL:** \ **Category:** Factual Questions\ **Created:** [December 16, 2015, 2:00am UTC](https://boards.straightdope.com/t/amps-and-volts-to-watts-conversion/740588 "2015-12-16T02:00:03Z")\ **Posts on this page:** 3\ **Page:** 3
**Author:** ![core](https://avatars.discourse-cdn.com/v4/letter/c/d26b3c/32.png) [@core](https://boards.straightdope.com/u/core)\ **Post date:** [April 3, 2016, 6:46pm UTC](https://boards.straightdope.com/t/amps-and-volts-to-watts-conversion/740588/41 "2016-04-03T18:46:28Z")
> [@Crafter\_Man](#): > > So yea, my power strip _should_ be O.K. when the load current is 15 A. But something still bothers me about it. I have heard quite a few stories (albeit anecdotal) about power strips melting or catching fire. Regular 120 V / 15 A wall receptacles (NEMA 5-15R / UL 498) do not seem to have this reputation. The most likely failure mode I can think of is the tabs not making good contact with the plug prongs over time causing heat, melting, and fire. I don’t think the UL standard says anything about how the device performs 10 years from now, but then again I haven’t bothered to read it. 🙂 Then again you could get similar issues with a $0.29 recep from the bargain bin at the big box store, but it’s a lot harder to get above 15A with only two sockets on a duplex recep. I think most of these fires are caused by user error, not adding up the VA for the 6 devices. 15A power strip on a 20A circuit, user is oblivious, and it’s easy to see where trouble would start. Which gives the power strips a bad name. If these strips all came with the button-type breakers then maybe there would be fewer fires. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [April 3, 2016, 7:05pm UTC](https://boards.straightdope.com/t/amps-and-volts-to-watts-conversion/740588/42 "2016-04-03T19:05:05Z")
> [@excavating\_for\_a\_mind](#): > > Funny. Reading Crafter Man’s post makes me want to take a power strip apart. Maybe see if I can improve it.Insidious. A good description. Curiosity is so inviting… > > . I know all about curiosity. When I was a kid there were quite a few things I was curious about. I took them apart. I caught hell from my Dad (with a belt) because even he could not put them back together. This was a learning experience, that’s for sure… ---
**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:** [April 4, 2016, 12:44am UTC](https://boards.straightdope.com/t/amps-and-volts-to-watts-conversion/740588/43 "2016-04-04T00:44:26Z")
> [@core](#): > > The most likely failure mode I can think of is the tabs not making good contact with the plug prongs over time causing heat, melting, and fire. I don’t think the UL standard says anything about how the device performs 10 years from now, but then again I haven’t bothered to read it. 🙂 Completely agree. So let’s compare a power strip to a standard 15 A/120 VAC wall receptacle. By taking both apart. 🆒 [Here is a folder showing how I took apart a brand new power strip](https://www.dropbox.com/sh/7zp68qrjpkidcur/AADKeLY9KDMP613qKe8pmSFja?dl=0). In pics 7, 8, and 9, I insert a plug into the contacts. You might be asking, “Where’s the spring??” Good question. I guess the “springiness” comes from the strips of brass that are in contact with the plug contacts. I’m not an ME, but I am skeptical the spring force can remain constant after many years of use based on this design. It just looks very sub-par in my book. (An electrical contact needs adequate pressure at the mating surface in order for the contact resistance to remain low. A decrease in pressure can cause the contact resistance to become excessive, which in-turn can cause excessive heating of the contact. A hot contact is a bad thing.) [Here is a folder showing how I took apart a brand new 15 A/120 VAC wall receptacle](https://www.dropbox.com/sh/4zrxiblir3omd0z/AADLVp1QmJxYDWJs-hUmMvhUa?dl=0). Note the large size of the contacts and “real” looking springs. I also noticed the insertion force was significantly greater when compared to the power strip. So I agree with **core** … these power strips might meet spec when they’re new, but I suspect the contact force decreases over time due to a crappy & cheap design. [Previous page](https://boards.straightdope.com/t/amps-and-volts-to-watts-conversion/740588.md?page=2)