No, I am not.
You, however, seem to be unclear on the concept of skin depth.
Skin depth is a measure of the depth to which the electric field penetrates the material. It is not, as you seem to believe, the depth at which the current flows.
IOW, you're wrong.
Speaking of unclear on the concept... an electric field is simply a field in which work is done on an electric charge -- IOW, where current flows.
You might want to grab yourself a high school physics text and [re]acquaint yourself with a few concepts before you so glibly assure CW that he's mistaken. First, it's *static* charge that resides on the surface of a conductor, *not* electric current. Second, the cloud of free electrons in a metal extends throughout it, rather than being confined to the surface.
Finally, you might want to ask yourself why the NEC-permitted ampacity of conductors below about 4/0 is [roughly] proportional to their cross-sectional area, not their diameter.
In a force field the potential to do work is present, whether work is actually being done or not. Surely you'll agree that the electric field extends beyond the wire into the surrounding air where no current flows.
You do not need current to have an electric field. Light is an example. The skin depth for light is real small.
Wikipedia has good articles on the subject.
OK, you got me there.
I wasn't familiar with the relationship between skin depth and current density. The current density at the center of #12 wire is almost 90% of that at the surface, right?
Last night I was thinking about this and remembered the Hall effect. That would not be possible without current passing through the conductor, rather than along the surface.
NOW, Mr CW can see me backpedaling.
The NEC tables make assumptions about heat-dissipation to the environment and 4/0 down to #8 conductors are typically multi-standed, both of which complicate the issue.
If we look at the DC resistances vs cross sectional areas for #10 and smaller in the table here:
How about closing an AC circuit through a capacitor? Would you agree that the AC 'passes' through the capacitor even though the electrons do not?
BTW, other than the description at the top of the page, I don't see any difference between NEC 310-19 and NEC 310-18 here:
Take a good look at a circuit board trace, if skin effect was a major problem most would behave similar to Windows 3.0
Mark (sixoneeight) = 618
OP: Can improper wiring cause a fire.
Yes.
Next?
I do feel a bit vindicated watching these last 120+ posts about moot points, discussed by a group of full-time arguers, most of those don't have a clue. Now prior to my last run in with a few of these mental giants, I would have taken pleasure in throwing a few bones to these gnarly pups just to see them flip out all over each-other. Chasing tails, drooling, panting, refusing to roll over and LOTS of yapping.
Did anyone see that wicked chropractical move they did on Hussein's neck? I don't know why they bumped him off, he would have made a great commentator on FOX news.
*singing* "Lord loves a hanging that's why he gave us necks"(Ren & Stimpy)
love,
r
Did that a long time ago (sixoneeight) = 618
Yeah, I'll go along with that.
I haven't run the numbers, but that sounds about right, maybe on the low side, even. [snip]
In a sense, anyway -- but I think we're splitting hairs. Certainly if you apply an alternating current to one side of a capacitor, you get an alternating current out of the other side too.
I didn't check every entry, but the first one appears to be correct. The second one is definitely *not* correct: they have erroneously reproduced
310.18 under the heading of 310.19. The two tables are in fact substantially different. >
The hair splitting is in how the phenomenon is described or measured, and it's easily confused by the base terms. In other words, the base term is "Alternating Current" which should describe voltage of a certain frequency.
In the capacitor scenario, the confusion arises because we tend to think of DC and its "flow of electrons." Obviously that flow must come to a stop at an open circuit, i.e. the capacitor. However, in AC, where the electrons only move a relatively short distance (and depending on frequency) before switching direction, the "effect" of electron flow is seen as being across the capacitor.
That "flow" is measured as current, which leads to the precept that AC flows through a capacitor and DC is blocked by it. In truth, however, although you can measure the current flow, and work is actually done, the electrons don't actually cross the capacitor.
I have no idea what I was trying to say there. I think I just mashed a couple thoughts together. Like I said, this was done quickly. Actually, the basic point there has to be something about smaller wire getting hotter for a given load, which would relate to the small size of the connector in the stab-in connection, which is what gets hot under load. As a matter of fact, the use of stab-in connectors is either banned or strongly discouraged in many areas now.
Re-reading that article there are a couple places I need to clean up.
-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"
Tim Douglass
Since this over milked subject won't die a natural death, I finally had to throw some gasoline on the fire.
---So:--- (1) "Also note that the amount of electricity that can flow....." Electricity having two attributes i.e.; Voltage and Current I shall assume you're referring to Current in this context?
(2) "with the most basic factor controlling resistance is the size of the wire." I shall agree if we ignore the type of material the wire is made of such as lead, copper, silver, gold, tungsten, aluminum, etc-ad-inifinitum. Just ask the toaster manufacturers !
(3) Are we now going to add surface current flow to our consideration of wire sizes to power our tools? And do we ignore the mechanical strength solder adds to a joint? Further, very few, in fact none of my stationary power tools run on DC, so I shall conclude that is "safe" to delete surface current comparisons of AC vs DC from this highly over technical evaluation of what started out as a simple.... Yes/No question?
But at least the Engineering theorists sure had fun with it didn't they? Not a lot of practicality here for application in the home shop , but a lot of smoke got blown and a lot of chest got beaten on!
Don Dando
and bring something to kill"
Could you summarize some of the maintenance issues?
Does anything need inspection and/or replacement more often than copper wire?
On Wed, 3 Jan 2007 12:49:12 -0700, snipped-for-privacy@spamcop.net wrote (in article ):
Check connection tightness perodically. The wide thermal expansion properties makes Al wire tend to work itself loose after awhile. Also be ware of any connecting devices (wire nuts, screw lugs, etc.) that are not specifically rated for Al wire.
That's kind of hard to do when the connections are inside of the wall, right?
NEC forbids connections that cannot be easily accessed. In this case, one must pull the device and torque the connections to the correct value for Al Wire.
Of course, the device itself must be rated for AL or AL/CU.
scott
You are in over your head sunshine, give it up.
Lew
[...] [...]
That, in and of itself, is sufficient to exclude the installation from the category of "properly installed" wiring, whether aluminum or copper. The NEC requires all junctions to be readily accessible.
Aha, so is removing the cover plate and then removing the switch or outlet from the box is readily accessible, tearing out the wall is where the line is drawn.
I sure wish those boxes were bigger, or at least DEEPER. I recently replaced a ground -fault breaker in a bathroom and it was a PIA.
I'm willing to bet that the number of homes that get that inspection ever, let alone periodically, is about nil.
In an earlier article (not sure if its part of this thread or an earlier discussion, someone suggested that for copper wire it was better to terminate it on the screw, rather than using the clamp. I assume he was referring to switches and outlets. I find that to be well-nigh impossible with #12. Is it acceptable to use crimped lugs, with two lugs on the same screw? Or is there really no problem with what Leviton calls 'back' connections?
I emailed Houston Wire to tell them about the error in their webpages. Thanks for checking.
Yep.
You can get deeper/bigger boxes, but they cost a lot more--far out of proportion to the size increase.
Chris
Absolutely.
Something to the effect of "without removing or damaging the structure or finish of the building" is where the line is drawn. Tearing out the wall would fall under that heading, but so would removing a piece of molding.
I assume you mean a GFCI *outlet*... Deeper boxes do exist, and they're frequently used in new construction, particularly where GFCIs are required.
I won't take that bet. :-)
True. It's *much* more secure.
Note that for aluminum wire, the clamp isn't even an option: you *must* use the screw.
Why? It's not that hard to bend a hook on the end of a #12 copper wire. Grab it with the tip of a needlenose pliers and twist. Or use an electrician's stripper-crimper tool (e.g. Gardner-Bender GS-70) -- most have a hole about
1/8" in diameter in one of the jaws, specifically for making such hooks. Stick the wire through the hole, twist the tool 180 degrees, and voila! a perfect hook.Yes, if the lugs are rated for 120V *and* the device is rated for two lugs. Of course, you could use one wire in a lug as a pigtail, and wire-nut it to as many other wires as needed.
Yes, there really is a problem -- they're not nearly as secure as originally believed. In fact, they're no longer listed for use with 14ga wire specifically because of that. They don't always grab 12ga as tightly as they should. Better to avoid them altogether, and just use the screws.
No prob.
snipped-for-privacy@spamcop.net wrote: ...
But (and I am asking this mostly for the lurkers) surely only with a proper (rated for aluminum) terminator on the wire. You are NOT allowed to use bare aluminum wire under a brass screw, that is a sure fire (no pun intended) recipe for disaster, right?
OK that'd work but then the heads of the screws would stand proud and the fixture would not fit back in the box. The GFCI (thank you) protects two 'downstream' circuits. Looks like one of those larger boxes is called for. And for a fumble fingers like myself, lugs.
When I rewire my home, which is currently a bastard mix of romex and knob and tube, I intend, wherever possible, to avoid both 'pass through' and splices behind the outlets, feeding them from separate junction boxes in the attic or crawlspace.
It is downright scary to discover that turning the lights on in my dining room causes an (unused) upstairs bedroom outlet to become hot to the touch.
But, as Mr Hodgett so diplomatically suggests, I've a lot to learn first.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.