Nickel coated copper wire

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Grouch1980

Grouch1980

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New York, NY
I came across a #8 AWG feeder that's comprised of nickel coated copper wire. The feeder runs from a meter center over to an apartment in a high rise residential building. The feeder is pretty old... maybe installed 30 years ago? I usually use table 310.16 of the NEC to get the wire ampacity... but that's for copper / aluminum / copper-clad aluminum wire.

Do I use table 310.18 to determine the ampacity of this type of wire? I never dealt with nickel coated copper wire. According to that table, the ampacity of the #8 wire would be 93 amps. Is this correct?
 
Any chance it is tinned copper. In that case I believe you would use table 310.16. I did not open the NEC, but #8 at 93 amps seems high
 
Table 310.18 is for high temperature insulated conductors used in specialized industrial applications.

You might see very high ampacites listed, but that is for running the wire at very high temperatures. More likely the ampacity would be seriously derated for high ambient conditions. For example using wire with 150C insulation in a 100C environment.

None of the above would apply to a residential feeder.

Far more likely you have tinned copper wire, where the tin coating was necessary to prevent reaction with the old rubber insulation.

I would treat the conductors as having 60C insulation unless you can confirm higher.

Jon
 
230724-1721 EDT

Grouch1980:

Nickle is non-porous in thin layers, and is used as an underlayer in chrome plating because it is non-porous. Automotive chrome surfaces are copper over the steel base for a good bond, nickle over copper for non-porous, and last chrome over the nickle, Thin layers of chrome are not non-porous. A very thin layer of nickle over copper wire should have virtually no effect on the resistance of a copper wire at power frequencies.

Three reasons for this: (1) there is virtually no increase in wire impedance at power line frequencies from a thin layer of nickle on the surface of a wire. (2) Nickle is itself a moderately good conductor.. (3) Only at much higher frequencies does most current flow at the conductor surface.

..
 
All the original circuits in my place are tinned solid copper in ridgid with some kind of plastic insulation. All westinghouse devices. Done sometime in the 50's. It's held up really well especially considering it was a repair shop for a mining company. It's outlasted stuff that was installed in the 80's
 
cannot recall the paragraph # of the formula for current rating of hightemp wires not speicifically covered by code, but that formula allows use of 260C rated Ni plated 18AWG wire to carry 30 amps.

An EMP fuse on a 30A missile silo motor circuit has a 1" piece of 18 AWG 260C wire, had to add a placard denoting hardness critical item to prevent electricians from removing it and replacing with a piece of 10AWG.
 
After powerline destroyed and site operating on batteries, open all 60 Hz lines or short them so EMP cannot get into site and damage electronics. EMP enough to fuse 18 AWG but maybe not 10 AWG. Fuses too low of long term reliabiity, CBs would just arc over.

This is for attacks where the nuke is close enough that the silo is tilted in the ground and diesels and powerlines all vaporized or zapped. Any more detail than that is still classified stuff.
 
In a residential situation you would use 310.16.

The only possible question is if you have to use 60C or 75C ampacity. That depends on the insulation and terminal temperature ratings.

The photo doesn't show the wire insulation, but that looks like a solid wire.

Solid wire is rare for building wire larger than 10ga.
 
A common place to see nickel plated wire is in motor leads. The wire is stranded, the strands seem stiff for their thickness, the insulation is braided yet stiff, usually in 2 or 3 layers. Expensive stuff
 
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