How to mark "110VAC" appilances for 12VDC

You can *physically* daisy chain them -- there is nothing that prevents you from doing that.

You can even get a "three prong" plug to fit into some (nothing made recently, IIRC) "two prong" extensions.

But, most extension cords are pretty cheap/flimsy. And, most "homeowners" see electricity as a *mechanical* phenomenon: "how do I get a continuous wire from point A to point B" never considering the bits and pieces they tack together to achieve that goal.

"Gee, why is this *wire* hot?"

I've got 100' of 12/3 stranded on a Hannay reel (nicely built product! But, very heavy -- maybe ~60 lbs) that I use whenever working in the yard, on the roof, etc.

By contrast, most homeowners will have some lightweight 14/16AWG cord strung across the yard. And, perhaps 15+A of holiday lights dangling off it!

Cords are also a trip hazard in a workplace. And, often result in "face up" outlets.

Here, the code requires outlets (receptacles) to be located at intervals not exceeding 12' (?) "along the baseboard". The thinking is that a user should be able to reach a nearby outlet with a ~6 ft corded appliance. WITHOUT needing an extension cord.

[On kitchen countertops, the distance shrinks to 4' between outlets as countertop appliances are intended to have very *short* cords]

The cord (and the appliances/devices plugged into it) have ratings. In theory, a user could/WOULD ensure that the ratings of all devices were observed when using them. As well as knowing how to derate cascaded cords (plug ten 6ft cords together to make a 60 ft cord; is the resulting cord capable of handling the same load as any of the *single* cords used to create it?).

But, as I said, most users just see electrical connections as a simple matter of "how do I get the right number of the right

*type* of connectors where I need them?" ["Let's see... this cube tap gives me three outlets! So, if I plug it into the end of the cord, the single outlet becomes 3 outlets! But, I need 6. So, I'll plug this second cube tap in as well. But, that consumed one of those three outlets leaving me with just 5 instead of the 6 (2 x 3) I had hoped for! So, I'll add a *third* cube tap -- which also costs me an outlet giving me 7 instead of the 8 I thought I was going to get..."]

Look at XMAS lights. They are designed to be cascaded for convenience. Plug the second strand into the end of the first. Indefinitely, right?? :> The strings that we use tolerate a maximum of three strings in a row -- the plug bodies of each are fused to enforce this restriction. Otherwise, you *know* someone would have "The Griswold's" (National Lampoon) house all fed from a *single* plug!

At last count, there were something like 57 "plugs" on various devices in my *tiny* office. (and that doesn't count the dozens of "peripherals" stored in the closet) I think, if I tried really hard, I *might* be able to find receptacles for each of them (there are six 6-receptacle FUSED outlet strips fastened to the undersides of the worktables -- no "face up" outlets allowed! -- plus at least two or three outlets on each of the 8 UPS's, also fused).

But, I don't *need* to have every device on at the same time (electric service couldn't support it if I did!) So, it's easier to just leave things unplugged (do I *really* need the four printers in that room "ready at a moment's notice"? What about the four scanners?) and bear the cost of manually plugging/unplugging as needed.

Granted, most folks don't have this much kit in their "home office" or bedroom. But, I'd wager most folks have *everything* plugged in at the same time! Even those items that seldom see use!

And, that many of these are NOT plugged into fused extensions or outlet strips. Rather, just whatever odds and ends (generic extension cords, cube taps, etc.) that they happened to have lying around -- to save them a trip to the store!

Reply to
Don Y
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Or a 15 plugged into a 7. The guy holding the end of the 15

*thinks* he's got a relatively high ampacity cord -- only to later discover the 7A "fuse" upstream! :>

There are reasons why certain appliances are expected to have "dedicated circuits"!

[I wanted to share the electric kiln with the swamp cooler on that 30A 220V circuit. It would be relatively easy for me to ensure both would never be on at the same time! But, apparently, this could only be done if the swamp cooler and kiln shared the same physical *outlet* -- plug one in or the other. "Um, isn't the role of the circuit breaker to protect against more power being drawn than the circuit rating? Doesn't *it* enforce that restriction on the load -- even if I *don't*?" In the end, it just wasn't worth a fight with the inspector... (and, SWMBO hasn't taken out the potters wheel, let alone asked for me to light the kiln! :-/ ) ]

Many homeowners with large TV's "hide" the wiring inside the wall behind the TV -- "Oh, that's *so* much cleaner looking!". This is a code violation. As is stringing an extension cord above ceiling tiles, etc.

Esp if the thing its hiding behind is not "movable" (intended to be removable), etc. You get into the whole "hidden box" syndrome.

Even abandoned wires are (technically) supposed to be removed from a structure -- lest they be reused "incorrectly". (IMO, a perfect reason NOT to use "conventional" electrical supplies like wire, connectors, etc. for "unconventional" uses).

[Actually, even speaker/audio wiring in walls is a no-no if the loads are large -- ~100W]

Bovinophobia? :>

Reply to
Don Y

No, it's the many-corroded-contacts-in-a-row problem. If you plug something like a space heater into a chain of extension cords, you can dissipate enough heat in the contacts that the plastic softens and an arc starts. The more you have, the more likely that is.

Most people won't pay the money for good extension cords, which is stupid, considering how long they last.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

Fire marshals will also ping you for extension cords used in a permanent installation. "Permanent" may just mean feeding a computer on a desk.

Reply to
krw

John Devereux schrieb:

Hello,

if you would daisy-chain a lot of extension cords, the voltage drop for large loads would be to high and the circuit breaker would not see enough current to break fast if there is a short circuit at the far end of the cords. There is maximum allowable resistance for a long cable between circuit breaker and load.

Bye

Reply to
Uwe Hercksen

Oh OK, so you are saying it is a probability thing.

--

John Devereux
Reply to
John Devereux

"Uwe Hercksen"

** LOL !!

Shorts in wiring dissipate no energy.

The extension cords leading to the short heat slowly, if the total resistance is so high breaker holds.

... Phil

Reply to
Phil Allison

Although in loose wiring they usually become plasma arcs pretty quickly.

They only heat slowly if the reel of cable is unwound. I caught our local church with two 3kW kettles plugged into a fully coiled up 20m extension cable last year - they were relying on divine intervention.

The year before they actually melted a reel. Now I know why and how!

Nominal 13A fuses take a while to blow even at 26A. The plug was really very warm when I got to it. I guess eventually it would have blown but probably not before another extension reel of cable was ruined.

(replacement now has a thermal cutout to protect against users)

--
Regards, 
Martin Brown
Reply to
Martin Brown

Phil Allison schrieb:

Hello,

if a short would dissipate no energy, why should the cord heat anyway?

Bye

Reply to
Uwe Hercksen

Really? Perhaps the cable has resistance? With 120V at one end and

0V at the other, something is going to get hot.

Not necessarily true. It's quite possible to have 16GA extension cords fed by a 20A circuit. The current limiting device is designed to protect the building wiring, not any device (or cord) plugged into it.

Extension cords are only for temporary use. "Permanent" installations are supposed to have outlets close enough that they're not needed.

Reply to
krw

** Yep.

** It will normally do both.

Extension cords barely get warm operating at their rated current.

It takes a 3 or 4 times overload to get to the PVC softening temp, so the breaker will go first.

I've done tests using a high current, low voltage source - have you ?

... Phil

Reply to
Phil Allison

Wrong. What about the rest of the statement?

Absolutely wrong. If that were true, there would be no electrical fires.

Idiot. The issue is FAULTS.

My, my, so you do understand that shorts will create heat.

Idiot.

Reply to
krw

True, but there's a lot of certifications that become invalid when DC is present instead of AC. I'd HOPE that any breaker or fuse for 120VAC would be OK at up to 28VDC, but only SOME such breakers or fuses have any DC certifications. The other issue is switching materials and gaps, there's significant arcing in a switch opening/closing, and DC will change the expected service life and failure modes. Wire and insulation (unless there's moisture present) should be OK with DC.

Reply to
whit3rd

krw= " krackpot ratbag wanker "

** Fraid it is absolutely correct - far as extension cords are concerned.
** Try reading ahead before making another ass of yourself - f****it.

** Like an idiot - you have not and have no idea of the simple facts.

Fuck off you damn troll.

.... Phil

Reply to
Phil Allison

Phyllis, you really need to learn to read. The issue isn't operating within ratings. The issue is *FAULTS*. If it were about "ratings" current limiting devices wouldn't be needed.

...the absolutes moron.

Reply to
krw

Bullshit. I see a lot of new brass 12 V lamp bases and sockets. It may oxidize if misused, but it doesn't rust away.

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

** It is complete fact.

I see a lot of new brass 12 V lamp bases and sockets.

** Which will tarnish and fail to connect in time.

Plugs and sockets that are intended for 12v DC use are all plated.

Same goes for audio connectors.

.... Phil

Reply to
Phil Allison

Um, Mike... brass doesn't rust. Only ferrous metals do that. Of course, I'm sure you knew that and were probably using the term "rust aw ay" in the more generic sense.

The way I learned it: Rust is to ferrous as tarnish is to non-ferrous. Rust is a chemical reaction with oxygen; tarnish is a chemical reaction wit h sulfur. Corrosion (not to be confused with either of the above), is a ch emical reaction with things other than oxygen or sulfur.

That said, brass tarnish is highly conductive, so Phil is still full of shi t. AND, it isn't a matter of the degree of "build-up", as he suggests because unlike rust, tarnish will STOP the moment the underlying base metal is no l onger in contact with sulfur in the air. In other words, tarnish forms a p rotective barrier. This barrier is highly conductive. Contact resistance does not increase.

See top of Page-17, this link on Brass:

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ng-the-right-brass.pdf

That's certainly true for Direct Current, which is the subject of this thre ad. At RF frequencies, I'm not sure what the conductive properties of brass sul fide are (assuming that's what you call it?) I would withhold judgment on that pending proof or testing, because at a high enough frequency, it is co nceivable that 100% of the RF currents, and therefore RF fields, would be t otally contained within the "tarnish" layer due to skin effect.

I'm sure Phil will have some snappy comeback to call me an A-hole or an idi ot, or whatever. Or maybe he'll surprise us all and just admit he learned something new.

Reply to
mpm

I would make that definition heirarchical: Corrosion is any atmospheric or aqueous oxidation process. (Chemical oxidation can occur with any oxidizer, including, but not limited to, oxygen.) Most metals corrode. Some self-limit in certain media, like aluminum and titanium in air and water; others, the layer develops so slowly at room temperature that it isn't a big deal most of the time (steel and copper are easily soldered, but a flux is required in both cases, for the same reason). Only the precious metals do not oxidize at all.

I would use two definitions for rust: strict and loose. Strictly, only iron (III) oxide (usually hydrous) is "rust". (Iron also has a lower oxide, but since it's produced at higher temperatures, it's called mill scale, or just scale.)

Loosely, any metal, whose corrosion process resembles iron's, can be said to rust. After introducing gallium or mercury to aluminum metal, it appears to "rust" away: the amalgam disrupts the oxide layer, which flakes off the same way rust does.

Lastly, tarnishing is a corrosion process, specific to near-noble metals, especially copper and silver. Sulfur has a particular affinity for these metals, above and beyond oxygen (the explanation is, to use a chemical pun, complex). Most metals can be tarnished, but most metals prefer oxygen over sulfur, and since sulfur is not a large constituent of the atmosphere, they form oxides instead. Tarnishing proceeds slowly on these low-reactive metals.

I'm not sure how conductive it is, but it is true that all copper sulfides are either semiconductors or metallic (like pyrite).

Now, brass is not just copper. "Brass" is generally a 5-35% zinc alloy, sometimes with other additions as well (3% lead for machining, etc.) Colloquially, anything "brassy" might be called brass, which is unfortunate. (The superset of copper alloys, bronzes, is classically only a range of tin alloys, but presently encompasses alloys containing anything from manganese to tellurium. Properly, a bronze must be qualified, e.g., "phosphor bronze" uses phosphorus as the primary addition. Brass could correctly be called "zinc bronze".)

So, the zinc will oxidize as well, often preferentially (which is neat, actually: if you've ever used an acid-core solder on brass, you've probably seen the surface instantly turn coppery as the zinc is leached out by the acid fumes!). I don't know if the zinc will form a mixed sulfide with copper, a sulfide of its own (ZnS is a wide-bandgap semiconductor, and probably an insulator), or an oxide (ZnO, same story). I'd lean towards separate sulfide or oxide.

Whether the zinc corrosion part is a problem depends. If the grains of copper sulfide reach the metal, you'll still get contact. If zinc oxide coats over the whole thing, you'll see intermittent contacts (much as with aluminum connections).

The nice thing, I guess, about skin effect is, it doesn't care about resistive layers. Depth is proportional to sqrt(rho), so -- as you might've guessed -- depth in an ideal insulator is infinite -- the field goes right through. Something that's a few times more resistive than copper (like brass or zinc) won't be much deeper, but something that's hundreds or thousands of times more resistive will simply pass most of the field to what's underneath.

This can backfire. Suppose you were a cheap bastard and wanted to silver-plate a cheap iron waveguide. A common plating process starts with the base metal (iron), which needs to be prepped for adhesion (flash copper). Copper and silver will diffuse together over time and ruin the plating, so a diffusion barrier is needed: nickel. Silver finally goes over the nickel, hopefully in a nice thick layer for the microwaves, and you're done. Why does it backfire? The silver plating might be thick enough (fraction of a thou, I think) to carry most of the microwave current, but if a little bleeds through, it gets trapped in the nickel layer, which has high permeability, causing a dramatically thinner skin depth despite its resistivity, and heating up worse than if you went for, say, solid brass waveguide in the first place.

Back to RF and tarnish...

A more serious problem for sensitive receivers may be rectification due to the semiconductive tarnish, introducing distortion and IMD. This has been mentioned before in regards to connectors and such -- if you need best performance, avoid bare metal (brass or copper), and avoid nickel and silver platings -- gold or other precious metal is the best way to go here. (I'd like rhodium plating myself -- it's tough and abrasion resistant, and far more expensive than gold. ;-) )

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

"mpm"

** Who is this steaming ,great f****it ??

There are none more STUPID that those who take everything they read on commercial web sites as if it is the word or god.

** Not it isn't.

It is high resistance and capable of insulting at 240VAC if the layer is thick enough.

I do not get my " facts " from advertising material on web sites.

I see it in the real world.

A place that congenital, autistic morons like mpm never even visit.

... Phil

Reply to
Phil Allison

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