reuse of common AC plugs: DON'T DO THIS! - Page 1
Forum section: electronics / beginners

author: linux-works
author_rank: Super Contributor
timestamp: June 03, 2014, 03:09:02 pm
content: simply shocking that someone would do this and even worse, that a big DIY site would encourage such bad behavior:hackaday.com/2014/06/03/solar-energy-provides-an-outlet-for-hurricane-related-woes/folks who are reading this: please don't even THINK of doing anything this dumb. hack-a-day is being very irresponsible by even showing to the world (a lot of beginners) this 'idea' of reusing power sockets for something lower voltage dc output sockets.just wow ;(

author: max666
author_rank: Frequent Contributor
timestamp: June 03, 2014, 03:34:01 pm
content: Oh wow! This post would be perfectly suitable for the 'Electronic Horror Gallery'.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 03, 2014, 03:46:46 pm
content: Yikes! And; why do that when you could just connect an inverter to the battery and have a real 120 VAC outlet that you could use ordinary equipment on?Also, am I reading that correctly that he used 22-26 AWG phone wiring for a long in-wall run carrying relatively high current? That is possibly even more horrifying than the misuse of the 120 V outlet. Using that kind of undersized wiring for an in-wall high current application is going to start a fire.

author: richard.cs
author_rank: Super Contributor
timestamp: June 03, 2014, 04:00:34 pm
content: Using the standard AC plug of a foreign country for low voltage distrubution is pretty common (like using schukos in the USA or USA outlets in Germany) and, combined with labelling, probably not too unsafe. Unfortunately that's not what he did.

author: mtdoc
author_rank: Super Contributor
timestamp: June 03, 2014, 04:38:45 pm
content: Quote from: ejeffrey on June 03, 2014, 03:46:46 pmYeah, that's the real issue - the ampacity of the wire, not the plugs. He initially had no fusing. Reading the comments, it looks like he's now added a 3 amp fuse. Still not adequate protection - maybe with 1 amp fusing but then what's the point - he'd only be able to use it to charge a phone or two or turn on a couple of very small led lamps.

author: SeanB
author_rank: Super Contributor
timestamp: June 03, 2014, 04:58:05 pm
content: The wire is the fuse........

author: jolshefsky
author_rank: Regular Contributor
timestamp: June 03, 2014, 05:27:20 pm
content: Omitted: the 12V equipment that has a 120VAC plug at the end! "Oh, AC plug, AC outlet?" :BANG:I see one big thing wrong with using mains wires for 12V, and it's not the current as long as it's limited to ~20A as per a household circuit. The big thing is unconventional wiring inside a house! When an electrician comes to do work at some point in the future, would jee know it's actually 12V and not mains? I find it bad enough when people use the non-standard (against U.S. code?) practice of hot-is-white / neutral-is-black (at a bare minimum people remember "black is death", because, you know, we're all raging racists here in the U.S.)

author: AG6QR
author_rank: Frequent Contributor
timestamp: June 03, 2014, 05:56:32 pm
content: Yeah, there are many comments on the Hack a Day site about this, and most of them are good. This is an accident waiting to happen. I'd use Anderson Powerpoles, or at least some other dedicated 12V connector, instead of a mains style connector. And the wiring gauge needs to be beefed up.The big problem isn't that someone will plug a 120V appliance into a 12VDC outlet. That might happen, but, especially if things are fused, the low voltage is unlikely to present a huge safety concern. The big problem is that the 12VDC appliance adapted to use that 12VDC outlet (that is physically like a 120VAC outlet) might be plugged in to a 120V outlet.His motive was reasonable, though. He wanted the ability to re-use his 120V table lamp fixtures on 12V during a power outage. He found some 12V bulbs with an Edison base, and screwed them in to his lamps. Now, he needed to get 12V into those lamps, and the easiest way is to put 12V into a 120V outlet.He mentions in his writeup that you have to be sure to remember to swap the bulbs back before you plug the lamp into 120VAC, and he says he almost forgot to do this. Yikes! With an incandescent bulb, it would probably just quickly burn out the filament, but he was using 12V LED bulbs with Edison bases. I wonder what sort of protection they have against 120VAC?The original problem is that the same Edison base is used for lamps of widely varying and incompatible voltages. Those sockets/bulbs are used in boats and RVs (camping vehicles) using 12V, but the same physical connector as is used for 120V bulbs.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 03, 2014, 06:08:19 pm
content: How is insurance if you get a fire due to this in the USA?

author: mtdoc
author_rank: Super Contributor
timestamp: June 03, 2014, 06:13:05 pm
content: Quote from: jolshefsky on June 03, 2014, 05:27:20 pmI disagree. Anything more than an amp or two through 22-26 AWG wire running through your walls is a huge fire risk. Yes, the wire would be the fuse long before you got near 20 amps...Any fire caused by this would not be covered by homeowners insurance.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 04, 2014, 02:27:37 am
content: Quote from: jolshefsky on June 03, 2014, 05:27:20 pmHe isn't using mains wiring. He had some *phone wiring* that he re-purposed for low voltage power transmission. That is cheap, poorly insulated narrow gauge wire. Not only that, if you are re-using existing wiring you never know where someone spliced a run by twisting wires together, or where you have a crack from metal fatigue on the thin wires that can create a local hot spot.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: June 04, 2014, 02:37:20 am
content: Can anyone suggest a good solution for wall mounted DC outlets? Be nice to give him an alternative.Something like wall mounted Andersons that kids cant put their fingers in.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: June 04, 2014, 02:39:50 am
content: The worst thing about what the OP has done is the equipment that plugs into it.It sure wont be expecting mains voltages and currents if it is accidentally plugged into a mains wall socket.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 04, 2014, 02:49:44 am
content: Quote from: HackedFridgeMagnet on June 04, 2014, 02:37:20 amBanana plugs or binding posts? They are not ideal, but they are cheap and easy to find. DC barrel jacks? DIN connectors? Regardless, with the low current wiring I think the idea is bad, not just the execution. The real solution is to use normal mains wiring and a 120 V inverter. Modified sine wave inverters are cheap and efficient and suitable for lighting and the switch-mode power supplies found in most electronics. Then you can use almost any device you want and you could power it from the line when available.QuoteIts 12 volt.

author: GeoffS
author_rank: Unknown
timestamp: June 04, 2014, 02:51:03 am
content: If I were doing it, I'd use a 2 pin, polarised socket like this. Safe and legal (in Australia)

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: June 04, 2014, 02:58:38 am
content: QuoteYeah but some might want to use more volts. And it might still hurt.Quote from: GeoffS on June 04, 2014, 02:51:03 amYeah I would use this too. Nice if we could get them at a decent price.Be even nicer if it was redesigned and optimised for this exact purpose.

author: Unknown
author_rank: Unknown
timestamp: June 04, 2014, 03:11:32 am
content: If this makes you cringe, don't ever look into what the slot-car afficionados do...http://www.slotcarsadelaide.com/controllers.htm#871524882http://slotblog.net/topic/42913-controllers-plugs-and-connections/http://owenduffy.net/blog/?p=1081

author: tsmith35
author_rank: Frequent Contributor
timestamp: June 04, 2014, 03:26:45 am
content: Quote from: ejeffrey on June 03, 2014, 03:46:46 pmIt's not so much the voltage: ampacity of 22-26 AWG wire is somewhere between 2.1 and 7 amps depending on how confined it is. That's somewhere between 25W and 84W at 12V. Telephone wiring does a pretty good impression of a glowing lamp filament if you pull too much current through it. Perfect for setting a house on fire, unfortunately.

author: mtdoc
author_rank: Super Contributor
timestamp: June 04, 2014, 03:50:35 am
content: Quote from: tsmith35 on June 04, 2014, 03:26:45 amWell said and agreed. But it's even worse:Enclosed 26 AWG wire has a rated ampacity of only 1.3 amps..

author: AG6QR
author_rank: Frequent Contributor
timestamp: June 04, 2014, 04:06:00 am
content: Quote from: HackedFridgeMagnet on June 04, 2014, 02:37:20 amYep, wall mounted Anderson Powerpoles are ideal for this purpose.I've got a camping trailer with both 120VAC and 12VDC systems. The 120VAC only works when plugged in to external utility power, which isn't always available, but the 12VDC system works off a flooded lead-acid battery that is charged by the tow vehicle's alternator while driving, so it works no matter where I'm camped.I installed some 12VDC outlets using wall mounted powerpoles, using thishttp://www.powerwerx.com/powerpole-accessories/powerpole-outlet-cover-plate-electrical-box.htmlHere's a photo of it in action:I took this photo while camped one evening, in a place with no utility power, so the white 120VAC outlets were dead, but the black Anderson Powerpole 12VDC outlets were working as always. They're powering an alarm clock with LED projection light, a AA battery charger, and a small portable inverter that produces 120VAC. The inverter is feeding a power strip and powering two camera battery chargers and an iPad charger.I've got more 12VDC Anderson Powerpole outlets elsewhere in the trailer which feed fans and LED interior lights.The wiring between the battery and the 12V wall outlet is properly fused 10AWG. And it's only about a meter long.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: June 04, 2014, 04:31:44 am
content: QuoteThanks I hadn't seen them. Obviously hadn't looked very hard.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 04, 2014, 04:49:42 am
content: Wow, maybe we should re-name this thread "How much can we possibly overreact?"Is using common mains connectors for some oddball power distribution smart? Not really.But what is the WORST CASE that could happen here?Someone could plug in a load that wants 120V (or 230V) conventional mains power.If he doesn't have the distro circuits fused, then that small-guage wire will act as a fuse and blow.Can anyone explain how this is "dangerous"? I will concede stupid, but not "dangerous".

author: ludzinc
author_rank: Unknown
timestamp: June 04, 2014, 05:14:03 am
content: Quote from: Richard Crowley on June 04, 2014, 04:49:42 amNote: Cable is rated for 1.3A, and there is a 3A fuse.Worse Case?You hook up a 120V appliance that 'doesn't work' but draws 3A. The cable slowly overheats, but doesn't fail. A small fire starts in the wall cavity.Everybody dies.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 04, 2014, 05:16:35 am
content: Ok, then I propose that the revised title of this thread should be "Don't forget the fuse!"

author: linux-works
author_rank: Super Contributor
timestamp: June 04, 2014, 05:19:01 am
content: does anyone remember the 'audio alchemy' company from a few decades ago? they used 1/8" trs male connectors on their dual-rail dc wall-wart psu's and mating female sockets on the preamps and dacs and things they made. and yes, this is a SHORTING plug. this is a shining example of misuse of a connector for power, and even worse, by a commercial venture that should know better. it always blew my mind that a company would pass their product from beta test to full manuf and no one would speak up and say 'hey, this is really dumb!'. there were lots of user reports of sparks happening when the plug was inserted into the dac box while the power cord was still plugged in at the wall side.so, its not just hobbyiests who do these dumb things with the wrong kind of jacks, even 'real' companies can be brain-dead at times.we should still call them all out for it. else, nobody learns.

author: linux-works
author_rank: Super Contributor
timestamp: June 04, 2014, 05:22:03 am
content: Quote from: Richard Crowley on June 04, 2014, 05:16:35 amno, its way more than that.you should always design plugs so that 'if it fits, it will work or, at least, do no harm'. good engineers try for this. and re-use of a same-type plug for low voltage and high voltage is just plain wrong. how do I know if this is a low-voltage device or a high-voltage one? color? really? not good enough. we can do better and this is a lazy short-cut.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 04, 2014, 05:30:54 am
content: Yes, we appear to be in "violent agreement" that it is a dumb thing to do.But highlighting the choice of connectors diverts the focus from the real problem here (wire gauge/fusing).We already have examples of standard mains outlets with additional USB "A" connectors (for charging gadgets).I agree that it may be a viable product to sell Anderson PowerPole panel-mount assemblies that fit into standard "decora" wall plates.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 04, 2014, 05:44:24 am
content: Quote from: Richard Crowley on June 04, 2014, 05:30:54 amWell the connector is also a potentially serious problem, although in this particular instance it doesn't sound major. For such a device to be useful, you need to have 12V devices that have a 120 VAC plug on them. Those will almost certainly be destroyed if they are accidentally plugged into a normal outlet, and they may not fail safely in such a situation. In his case thankfully he isn't splicing NEMA plugs onto arduinos, but using 12 V lamps with Edison bases and using them with fixtures rated for 120 V. We can hope that the bulb manufacturer realized that this could happen and designed them with enough electrode separation to safely clear an arc if they are connected to 120 V. There is no guarantee, but it is pretty likely to be fail-safe. As soon as you want to hook something else up to your "12V backup power" and start adding mains plugs to low voltage equipment you are in trouble again.So really both problems are not just stupid, but dangerous and potentially deadly.

author: Psi
author_rank: Super Contributor
timestamp: June 04, 2014, 06:05:35 am
content: We used to have 12V lamps that looked the same as the 240V ones (Bayonet mount) around the house.They were used in the garage which was all 12VEvery so often someone would plug one into a house 240V socket with predictable results

author: mtdoc
author_rank: Super Contributor
timestamp: June 04, 2014, 07:19:02 am
content: Just to flog this horse a little more.....The initial article did not mention anything about fusing. Just "hook up your 12V batteries to your phone cable, put in a standard plug and you're good to go" was the gist of it.Only later, in the comments, does the author says he added a 3 Amp fuse so all was ok..The thing is a 26 gauge wire will get quite hot with just a few amps and could easily start a fire if in contact with the wrong material. I've seen old houses in the USA with balled up newspaper stuffed in the walls for insulation and wiring running right along through it..So yes, the plug is an issue - but the real danger - as in burn down your house danger - is using a too small and unfused or inadequately fused wire to carry too much DC current.OK proceed with burial of said horse.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 04, 2014, 07:19:55 am
content: Quote from: Richard Crowley on June 04, 2014, 04:49:42 amNo!The Worst case is that someone has a 12v device with a standard 120v type plug on it,& plugs it into areal120v outlet.If they have a bunch of 120v lamp units with 12v light bulbs or LED replacements in them,the worst that could happen is to blow up the bulb or LED lamp (big "bang"),as the insulation will still be OK for 120v.It will,however, be tempting to use other equipment,designed& insulatedfor 12v with one of these plugs fitted.Not only a big bang as before,but now,there is the distinct possibility of the external metal work of the "12v" device being connected to the Live side of the mains.

author: corrado33
author_rank: Frequent Contributor
timestamp: June 05, 2014, 04:51:53 am
content: Quote from: AG6QR on June 04, 2014, 04:06:00 am100% off topic but I don't know how much I'd consider "that" camping...(But to each his own.)Slightly more on topic. I just remembered I have a 120V outlet that doesn't work on the other side of my room (behind my bed.) I should REALLY check that out.On topic: I've always hated variacs that use standard wall sockets for their output. I miss simple binding posts! However you could always plug the variac into itself (infinite power?)

author: Monkeh
author_rank: Super Contributor
timestamp: June 05, 2014, 05:34:43 am
content: Quote from: corrado33 on June 05, 2014, 04:51:53 am

author: Jeroen3
author_rank: Super Contributor
timestamp: June 05, 2014, 05:35:41 am
content: Luckily you can put banana plugs in EU mains sockets.But infinite energy sounds good enough.

author: Rick Law
author_rank: Super Contributor
timestamp: June 05, 2014, 05:46:44 am
content: Ah ha... You guys don't get it. This is a grand experiment to see if evolution still works. It is an attempt to clean up the human gene pool.There must be a load of Dawin Award trophies in a warehouse somewhere ready to dispatch to the winners, express shipped to ensure it arrives at the funeral home in time for the viewing and/or wake.

author: VK5RC
author_rank: Unknown
timestamp: June 05, 2014, 06:10:57 am
content: My problem is the spectrum of Darwin award 'nominees' who don't quite kill themselves and end up in hospital for a long time costing tax payers huge amounts. It might be simpler to use a purpose built plug and socket:-)

author: BillyD
author_rank: Regular Contributor
timestamp: June 05, 2014, 09:43:10 am
content: Reminds me of a time when I used to work in a tool hire company and one day they purchased a brand new electric vibrating poker with a 'funny looking' plug on it. Shortly afterwards a customer arrived looking for a poker so the funny looking plug was quickly replaced with a 'proper' 13A plug (220v) and out it went out on hire.Apparently the word 'vibrate' didn't even come close to describing how it performed when it was powered on.Sadly it couldn't stick the pace for very long and it arrived back at the workshop later that day, dead.Yes the funny looking plug was a US 110v one. Don't know how it ended up in Ireland.But I agree with what others have said above; there are at least two howlers here.It's only a matter of when, not if, somebody accidentally plugs one of those 12v devices into a mains socket. And pumping any more than a couple of amps through that phone wiring is a recipe for a slow burn somewhere.

author: krivx
author_rank: Frequent Contributor
timestamp: June 05, 2014, 10:21:58 am
content: Quote from: BillyD on June 05, 2014, 09:43:10 amI thought 110V tools were common here on construction sites for safety reason, are the plugs normally different?

author: BillyD
author_rank: Regular Contributor
timestamp: June 05, 2014, 12:42:30 pm
content: Quote from: krivx on June 05, 2014, 10:21:58 amYou're right, in fact I think 110v may even be mandatory on building sites here now. But these all use 16A IP44 plugs or better, whereas in this case the original plug was a flimsy little 2 pin domestic US plug.

author: krivx
author_rank: Frequent Contributor
timestamp: June 05, 2014, 02:32:43 pm
content: Quote from: BillyD on June 05, 2014, 12:42:30 pmI had to google IP44 - yes, I have definitely seen a lot of those on tools and on transformers.

author: Monkeh
author_rank: Super Contributor
timestamp: June 05, 2014, 02:34:47 pm
content: IP44 is an ingress protection rating.IEC 60309are the connectors.