# Electric circuits in old houses--the Random Approach

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• posted on November 1, 2006, 12:33 am

On Tue, 31 Oct 2006 18:48:45 -0500, "Proctologically Violated©®"

Sounds unlikely.

There is a "skin effect" for AC signals but it doesn't become significant until you're into Megahertz if memory serves. At 60Hz it's probably nearly unmeasurable.

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• posted on October 31, 2006, 11:51 pm

I think you should go read 310.16 again. The difference in ampacity depends on the isnulation temperature rating (except aluminum which is generally one size bigger for a given ampacity) The "tinned" wire is lead coated and that does not change the ampacity
That is all academic in sizes 14-10 anyway since 240.4(D) rules 10ga -= 30a 12ga = 20a 14ga = 15a
There are very few exceptions to this rule. None affect a circuit with receptacles on it.
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• posted on November 1, 2006, 1:08 am
OK, you forced me get my NEC--and my magnifying glass.
I did overstate my case, but look at Table 310.19:
For #4 wire, for example, the four ampacities are 190, 220, 150, 278, where 278 is nickel coated copper. And the 150 is bare wire?? Strangely, for #12, the ampacities are 60, 68, 35, 78.... really high! Special insulation?? For the nickel-plated wire, the ampacity is higher, but the temp is also notably higher, and the insulation is different in all cases, so it sorta seems like the plating is helping, but too much other stuff is happening.
Actually not sure if the coating on my wire is nickel or lead, but it seems brighter/smoother than what I would imagine lead would provide.
Oh well, not as dramatic as I thought... :( -- Mr. P.V.'d (formerly Droll Troll), Yonkers, NY Stop Corruption in Congress & Send the Ultimate Message: Absolutely Vote, for *Anyone BUT* a Democrat or a Republican Ending Corruption in Congress is the Single Best Way to Materially Improve Your Life entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie, all d'numbuhs

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• posted on November 1, 2006, 2:54 am
On Tue, 31 Oct 2006 20:08:08 -0500, "Proctologically Violated©®"

You should have looked at 90.1(C) Intention. This Code is not intended as a design specification or an instruction manual for untrained persons.
The table you are looking has nothing to do with residential wiring. That nickle wire is either a high temperature fixture wire or part of MI cable (something most electricians have never seen). Niether of these are used in a home. Look at the temperature ratings of those wires. 302 degrees F up to 482F. If you have old Romex it is 60C max (140F), for that matter that is all you can use new Romex for in basic ampacity. (the first column in 310.16) The 90c column is only valid for derating purposes. As I said upthread, the over riding rule is 240.4(D) and that is the old 10ga0a, 12ga a, 14gaa. The only exception that affects homeowners is usually the dedicated motor circuits like the condenser on a split system AC unit. In that case you can use the label on the A/C unit to select the wire and breaker combination. That was an engineered circuit dedicated for a motor.
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• posted on November 1, 2006, 4:05 am
Why is the wire in the table I cited rated so high? Triple the normal rating, for #12? -- Mr. P.V.'d (formerly Droll Troll), Yonkers, NY Stop Corruption in Congress & Send the Ultimate Message: Absolutely Vote, for *Anyone BUT* a Democrat or a Republican Ending Corruption in Congress is the Single Best Way to Materially Improve Your Life entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie, all d'numbuhs

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• posted on November 1, 2006, 5:17 am
On Tue, 31 Oct 2006 23:05:57 -0500, "Proctologically Violated©®"

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. http://en.wikipedia.org/wiki/Mineral-insulated_copper-clad_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.
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• posted on November 1, 2006, 8:09 am

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--
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• posted on November 1, 2006, 5:46 pm

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.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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• posted on November 1, 2006, 6:16 pm
On Wed, 01 Nov 2006 17:46:06 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

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.
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• posted on November 3, 2006, 6:11 pm
Chris Lewis wrote:

I'm not aware of where frequencies, other than 60Hz, are specifically covered in the NEC. There are tables for wire reactance at 60Hz which would not apply. Power other than 60Hz (or 50Hz, some 25Hz still?) is probably rare and would be engineered. There are some NEC provisions for harmonics.
There used to be a NEC correction table for converting DC resistance to 60Hz "AC resistance". For wires not in metal conduit I think that is primarily skin effect. The table was in the 1978 NEC, removed by the 1990 NEC. A few values wire size correction multiplier 1 1. 0000 1.004 500MCM 1.018 2000MCM 1.233
The correction is under 2% at 500MCM which is really big wire.
-- bud--
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• posted on November 1, 2006, 5:40 pm

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).
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Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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• posted on November 1, 2006, 6:08 pm
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! -- Mr. P.V.'d (formerly Droll Troll), Yonkers, NY Stop Corruption in Congress & Send the Ultimate Message: Absolutely Vote, for *Anyone BUT* a Democrat or a Republican Ending Corruption in Congress is the Single Best Way to Materially Improve Your Life entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie, all d'numbuhs

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• posted on November 2, 2006, 7:25 pm
says...

It occurs at much lower frequencies than that. I'm retired from NASA, and worked on the electrical system for the Space Station. The original power plan was for 20 Khz power at 160 volts, and we had numerous testbeds running 20 Khz switchgear and instrumentation. It most definitely exhibits surface effect. The most efficient wires we tested were thin, flat ribbons about 2 inches wide and maybe 0.010" thick. They were stacked together for higher amperages, each ribbon insulated from the others.
On of the claimed advantages of the 20 Khz power was safety, the current would flow around the outside of an astronaut if they contacted a live conductor.
-- Dennis
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• posted on November 2, 2006, 3:03 am
snipped-for-privacy@gannon.edu says...

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.
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snipped-for-privacy@phred.org is Joshua Putnam
<http://www.phred.org/~josh/
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• posted on November 2, 2006, 4:34 am
Do all insurance co's inspect houses? I don't ever recall that happening. -- Mr. P.V.'d (formerly Droll Troll), Yonkers, NY Stop Corruption in Congress & Send the Ultimate Message: Absolutely Vote, but NOT for a Democrat or a Republican. Ending Corruption in Congress is the Single Best Way to Materially Improve Your Family's Life. entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie, all d'numbuhs

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• posted on November 2, 2006, 5:11 am
entropic3.14decay@optonline2.718.net says...

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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snipped-for-privacy@phred.org is Joshua Putnam
<http://www.phred.org/~josh/
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• posted on November 4, 2006, 2:33 am
I've never heard tell of such an action in all my days. Maybe a picture or two from the outside, but that's it.
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Steve Barker

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• posted on November 4, 2006, 3:14 am
Steve Barker LT wrote:

I know of 3 people who went thru this, one was denied insurance completely home had really bad roof....
One had to replce their K&T wiring and rebuild their porches....
One was required to replace their sidewalk, tree roots had lifted slabs, it was a trip hazard.
state farm will not insure homes with K&T I asked the other day when I was in their office....
insurance companies dont want claims....... homeowners used to be a cash cow but the hurricanes changed all that........
its just like car insurance, have a DUI or two, espically a license supension? its assigned risk for you..
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• posted on November 4, 2006, 4:47 am
Well I don't know about most K&T houses left today, BUT, I can assure you the romex job I tore out of our recently purchased 1871 home (wired in the late '40's) was a whole hell of a lot more dangerous than any K&T jobs I've seen. In a few months, I'll post the links to some pictures.
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Steve Barker

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• posted on November 2, 2006, 8:42 pm

trouble with crimps if something needs changed you may not be able to get the crimp apart necessitating wiring replacement. some leave no spare cable at all, i hate that