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17 years ago
This is wire normally used in high heat applications, hence the ratings in hundreds of degrees. The other part of the puzzle is the derating table at the bottom of the one you used. If you actually used this wire at that heat you would be derating it to 35% of the ampacity in the table. Again this is not a normal building wire. It is something you might see in an industrial kiln or a carbon arc light in the case of fixture wire or MI cable in interconnecting these appliances. MI cable looks like copper tubing with a powder inside that acts as the insulator. As I said, 99% of the electricians in the world have never seen MI cable.
Your wire is just regular copper with a very thin lead "tinning". This is a relic from the time when electricians soldered their connections. Tinning the wire makes soldering easier. It will have to use the 60c column of table 310.16 because the insulation is type TW.
I believe the purpose of nickle plating is to protect the copper from oxidation at high temperatures. It allows the copper to be used at a higher temperature (and if you used it at higher ampacity there is higher voltage drop).
As Greg G said, skin effect is substanitally negligable at 60Hz. There used to be (probalby still is) a correction table in the NEC for skin effect which only affected ratings, slightly, with very large wire.
-- bud--
State Farm in Minnesota a few years back had a surcharge for services older than xx years. They were forced to drop the policy by a class action suit or state regulators, don't remember which.
In the previously posted link
It is not a secret that insurance companies would like to redline neighborhoods.
-- bud--
Try looking for Ideal
30-210 30-211 30-222 The title was set screw connectors.My favorites are wire nuts with a "live spring" that deforms and expands over the wires.
-- bud--
In a previoulsy posted link:
-- bud--
how does anyone inspect anything buried in a wall, most likely buried under flammable lath and plaster?
that wiring without grounds is way past its design life.......
snipped-for-privacy@aol.com wrote: ...
So am I... :)
...
OK, I had a chance to go look for the previous link again...it's here--
I read the other paper as well but wasn't able quickly to find the reference cited in the following paragraph so what is lacking there is the information on how much external insulation was actually required to cause the overheating problem. IME it is likely for a "non-looped" run of wire not carrying over its rated ampacity to be far more than would be found in virtually any residential cavity for a structure of the age that would have K&T.
I wasn't arguing against, simply adding another piece of information and a link to a pretty informative paper, overall.
Here follows the section on K&T (which again doesn't say it is necessarily a problem, but that under certain circumstances _could be_ a problem)...
Excessive thermal insulation
There are simple ways in which a fire can be created with an electric cord that is neither damaged nor subjected to a current in excess of its rated capacity-loop it up upon itself several times, or provide a high amount of external insulation, or both. Laboratory demonstrations have verified that ignition readily occurs [ [28] ]; in one case, simply coiling the cord three times and covering with a cloth sufficed [ [29] ]. A special form of this hazard occurs with the old knob-and-tube wiring, which was common in the US prior to World War II. This type of wiring uses two separate conductors which are not grouped into a cable, but are individually strung on widely-spaced porcelain knobs. The current-carrying capacity is dependent on there being unobstructed air cooling of the wires, and fires have occurred when the wires were buried in thermal insulation [6]. .... [6] . Smith, L. E., and McCoskrie, D., What Causes Wiring Fires in Residences, Fire J. 84, 19-24, 69 (Jan/Feb 1990).
According to Noozer :
This is called skin effect. At 60hz it's so small an effect you can't measure it.
It's _totally_ ignored until you're into the 10s or 100s of megahertz. Eg: UHF.
Plating generally is for corrosion or galvanic protection.
I don't think nickel is higher conductivity than copper anyway.
I suspect that he's misremembering the clause in the 1996 NEC, or, he's missing context, and is misattributing an ampacity difference to plating, when it's really something else (aerial wire, higher temperature insulation etc).
Was it for 60hz? I believe the NEC does have provisions specific to frequency. I believe the NEC is intended to cover "distributions" of voltages in certain ranges, and thus, it'd have to make allowances for frequencies other than 60hz. Eg: 400hz systems.
You, and others, are most likely correct--also about the conductivity of nickel, which again defeats the purpose of plating for conductive purposes. I was really hopin my 14 ga wire was SILVER plated, and good for about 40-60 amps! :) No such luck. :( But, I got nicely soldered splices!
We did a lot of 400hz wiring in the old mainframe computer biz. They did make assertion that skin effect was present at 400hz and all of the cables on the computer side were fine stranded like a car battery cable. The sparkies on the line side still used garden variety THHN. Because of the typical sizes this was going to be stranded but it was the usual THHN stranding. I can't say we noticed any difference in voiltage drop from one side to the other. I think it was snake oil.
Bud-- wrote: ...
I guess that is so...I tend to forget/ignore/am unaffected from most if not all of those problems by being in smaller market areas and that dealing w/ regional/local firms instead of the national big boys is really a completely different experience..I guess not everybody has the luxury to choose... :(
Never the less, the system is as safe as it was when installed IF it hasn't been compromised or insulated around. The 286 computers will still do as well at word processing as they did the day they came out.
Amen!!
I still have my 286. Loved my amber monitor--was hi tech,back then! Loved Dos 3.3! :)
:Ultimately you are better off updating your electrical since it will: : :1. Improve safety due to grounds, GFCIs, AFCIs and load capacities that :meet today's standards. : :2. Improve the homes value and saleability. : :3. Avoid insurance cancellation hassles. : :4. Lower insurance premiums. : :5. Eliminate one possible excuse for denying or shorting a claim.
Plus it will give you an opportunity to install a whole house surge protection system.
When we insured my current house 2 years ago, it was still mostly K&T. The insurance inspection took hours, up into the attic, down in the crawlspace, pulled outlets and fixtures to inspect connections, etc., and ended up with exactly that decision -- the wiring was old, but safe. The inspection wasn't by an electrician, but by the company's senior loss adjuster for the state, who has significant experience with what goes wrong with old wiring.
The underwriting rules they were working from don't actually say "no K&T," they say no wiring that is obsolete, overloaded, or in need of repair, and no service panels under 60A. We can insure homes with K&T, or with fuses, *if* the wiring is in good condition and adequate for likely uses.
Do all insurance co's inspect houses? I don't ever recall that happening.
No, but it is becoming more common.
Most insurance inspections are exterior-only, sometimes just a drive-by with photos. Those are mostly to make sure the house is in reasonably good condition with no obvious undisclosed liability exposures -- the insurance company doesn't want to be providing premises liability to homes with un-fenced pools, or commercial operations in the garage drawing customer traffic. There's a good chance you could have had one of those inspections and not even know it, unless your house is inaccessible and they needed your cooperation to take exterior photos.
Different insurance companies have different underwriting requirements for homeowners insurance. Preferred-rate companies can be very picky, they refuse to insure houses that have any number of issues -- too many leaves in the gutter or moss on the roof, comp shingles that aren't leaking yet but are nearing the end of their useful life, trampolines on the premises, grass that's too tall, cars stored on the property, general clutter, anything that suggests an increased risk of losses. That pickiness means they can charge less for the homes they do insure.
At the other extreme there are companies that will insure a house with a roof that already leaks, they'll just add a roof exclusion to the policy. They know they're insuring riskier houses, so their premiums are higher, and they may sometimes be more detailed in their inspections: they know the house isn't perfect, they want to know just how imperfect it is. They have a long list of exclusions available for all sorts of non-standard risks. Getting non-renewed because you've had three theft losses? No problem, here's a policy with a theft exclusion. They don't like your EIFS siding any more? Try a policy with a siding exclusion.
When we insured my house, besides having K&T wiring, it had a broken foundation, which the inspector took a long look at before deciding it was still acceptable.
Once we finish our renovations, the insurable value of the house will be about triple its original value, but our premium will be lower.
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