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Copper Supply and Precision Machining in Oshkosh, WI — C101, C110, and Tellurium Copper

The electrical architectures inside modern defense vehicles and heavy equipment are dense with copper — battery cables carrying hundreds of amps, grounding straps bonding chassis to engine and body, bus bars distributing power from main circuit breakers to load centers, and precision-machined terminal blocks connecting wiring harnesses to high-current distribution systems. In Oshkosh, where Oshkosh Corporation builds vehicles that must start and operate reliably at -40°F on Alaskan test ranges and at 130°F in desert environments, the copper in those electrical systems is not a commodity decision. Grade matters: C110 ETP copper handles most wiring and bus work, C101 OFC (oxygen-free) is specified where connector reliability in vibration-intensive environments demands maximum conductivity and ductility, and tellurium copper replaces pure copper in precision-machined terminals and switch components where machinability must be dramatically improved without sacrificing too much conductivity. ManufacturingBase connects Oshkosh buyers with copper suppliers and job shops that understand these distinctions.

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Modern defense tactical vehicles are substantially more electrically complex than commercial trucks. JLTV and similar platforms carry integrated communications systems, electronic warfare equipment, vetronics (vehicle electronics), GPS navigation, and auxiliary power systems that together draw tens of kilowatts of continuous electrical power in addition to the drivetrain loads. The copper wiring harness weight in these vehicles exceeds 100 lbs in some configurations, and the bus bar and terminal block infrastructure distributing that power adds additional copper weight. Every electrical connection is a potential failure point in a combat environment, and the copper alloy grade, contact geometry, and surface finish at each interface directly affect system reliability over a 20-year service life. Ground straps — flexible woven copper braid connecting chassis components, engine block, and body to the main ground reference — are a specific copper product form critical to vehicle electrical system integrity. Electrolytic tough pitch copper (C110) braid provides the high conductivity and flexibility needed for straps that must accommodate relative motion between connected components over thousands of vibration and thermal cycles. Oshkosh defense vehicle programs specify these straps to MIL-DTL-16232 or equivalent, requiring documentation of conductivity and cross-sectional area to verify current-carrying capacity. Copper bus bars distributing primary power from battery banks to load centers are typically machined or cut from C110 or C101 flat bar and plate, with silver-plated contact surfaces to prevent oxidation at bolted joints. Hydraulic system components in access equipment and defense vehicles also use copper alloys selectively. Copper-beryllium alloy bushings and thrust washers appear in hydraulic pump and motor assemblies where the combination of hardness, wear resistance, and non-sparking properties is required — though copper-beryllium's health hazards in machining (beryllium dust) require strict OSHA compliance. Standard C110 copper tubing is used in low-pressure hydraulic pilot lines and fuel system connections where the material's ability to be formed to complex shapes by hand without specialized equipment offers installation advantages in dense engine compartment packaging.

C101, C110, and Tellurium Copper — Which Grade for Which Application

C110 electrolytic tough pitch (ETP) copper is the most widely produced and distributed copper alloy in the world, with minimum 99.9% copper purity and oxygen content of 100–650 ppm. Its electrical conductivity is 101% IACS (International Annealed Copper Standard) — essentially the reference standard for copper conductivity — making it the default choice for bus bars, wiring lugs, grounding hardware, and any application where maximum electrical conductivity at minimum cost is the primary driver. C110 is available in flat bar, round bar, sheet, tube, and rod from regional metal distributors in the Fox Valley area. Its softness (Rockwell F scale 40 in the annealed condition) makes it excellent for cold bending and forming but poor for precision machining in CNC applications, as it tends to smear on cutting tools rather than producing clean chips. C101 oxygen-free (OF) or oxygen-free high-conductivity (OFHC) copper eliminates the oxygen content that can cause embrittlement in hydrogen-atmosphere or vacuum brazing operations. With a minimum 99.99% copper purity and 101% IACS minimum conductivity, it is specified for electrical connector bodies, waveguides, and precision components where hydrogen embrittlement during soldering or brazing operations is a concern. The oxygen-free designation also indicates a higher-purity processing route that results in better grain structure uniformity — relevant for components that must maintain mechanical properties after cold forming. C101 commands a price premium over C110, so it should only be specified when the oxygen-free requirement is genuine rather than used as a generic copper upgrade. Tellurium copper (C145, 0.4–0.7% tellurium) is the machining-optimized copper alloy that solves the central problem of CNC copper work: the difficulty of producing clean chips from pure copper. Tellurium additions create second-phase particles that act as chip breakers, converting the gummy, stringy chips produced by C110 into short, manageable chips that clear the cutting zone cleanly. This dramatically improves machinability — C145's machinability rating is approximately 90 (versus 20 for C110) — while retaining approximately 95% of pure copper's electrical conductivity. For precision-machined terminal blocks, connector pins, electrical bus components with complex geometry, and switch contacts that require close tolerance turning and milling, tellurium copper is the material of choice in Oshkosh's heavy vehicle and defense component supply chain.

Machining and Fabricating Copper in Oshkosh-Area Job Shops

Copper machining requires different tooling and process approaches than steel or aluminum, and buyers sourcing copper components in Oshkosh should confirm that candidate shops have experience with the specific alloy grade they need. C110 and C101 pure copper's gummy cutting behavior demands sharp, high-positive-rake tooling with polished flute surfaces to prevent built-up edge — the phenomenon where work material welds to the tool face and then tears out, producing rough surface finish and unpredictable dimensions. High surface speeds (above 600 SFM with carbide), aggressive feed rates to maintain chip thickness, and flood coolant to prevent adhesive tool wear are the standard protocol. Even with optimal tooling, hole tolerances in pure copper are harder to hold than in steel because the material springs back more after cutting — ream passes with oversized starting holes are common practice for tight bore tolerances in C110. Tellurium copper (C145) changes this picture substantially. Its machinability improvement allows shops to run C145 at parameters similar to free-machining brass, producing clean chips, excellent surface finish, and consistent dimensional control at significantly lower tooling cost. For programs requiring hundreds of machined copper terminals or connector bodies, the shift from C110 to C145 can reduce per-piece machining cost by 30–50% through faster cycle times and longer tool life. The trade-off is that tellurium copper's slightly lower conductivity (95% IACS versus 101% IACS) and its slightly different mechanical properties must be acceptable for the application — for most electrical connection hardware, both properties are well within acceptable limits. Braze joining of copper components is common in bus bar fabrication and heat exchanger construction. Copper's high thermal conductivity means brazing requires high heat input — a focused oxy-acetylene or induction heating approach rather than propane torch — to bring the joint area to the silver braze flow temperature (typically 1,200–1,400°F for BAg-series silver alloys) before the surrounding mass absorbs all the heat. Shops experienced in copper brazing maintain proper technique documentation and use the appropriate BAg alloy for the copper-to-copper or copper-to-brass joint material combination. Flux selection is critical — residual brazing flux on electrical components can cause corrosion and increased contact resistance over time if not thoroughly cleaned after brazing.

Frequently Asked Questions

Tellurium copper C145 is the correct grade for precision CNC-machined terminal blocks, connector bodies, and bus bar components with complex geometry. Its machinability rating of approximately 90 (versus 20 for C110 ETP copper) allows shops to run at faster speeds with cleaner chip formation, achieving ±0.001 in dimensional tolerances consistently. Electrical conductivity of C145 is approximately 95% IACS — slightly below C110's 101% IACS — but for terminal and connector applications where the contact resistance is dominated by surface conditions and joint pressure rather than bulk material conductivity, the difference is negligible. Specify C145 by UNS designation on drawings, not just 'tellurium copper,' to ensure the correct temper (typically half-hard or hard for machined parts) is sourced. For simple bus bar shapes that are cut and drilled rather than turned on a lathe, C110 flat bar is cost-effective and adequate.
C110 ETP copper contains 100–650 ppm dissolved oxygen as cuprous oxide, which exists in grain boundaries and interstitially in the copper matrix. This oxygen is harmless in normal room-temperature electrical applications. However, when C110 copper is heated in a reducing atmosphere containing hydrogen — such as during hydrogen furnace brazing, annealing in forming gas, or certain vacuum soldering operations — the hydrogen diffuses into the copper and reacts with the cuprous oxide to form steam. Steam cannot diffuse out, creating internal voids and embrittlement that can catastrophically reduce ductility and electrical conductivity. C101 OFHC copper avoids this entirely by specifying maximum 0.001% oxygen content. In Oshkosh defense programs, specify C101 whenever copper components will be joined by hydrogen-atmosphere brazing, vacuum brazing, or soldering operations where the thermal profile could trigger hydrogen embrittlement. For standard room-temperature assembly and non-thermal joining, C110 is adequate and less expensive.
Regional metal distributors in the Fox Valley and Milwaukee area typically stock C110 ETP copper flat bar in widths from 0.500 to 4.0 in and thicknesses from 0.062 to 0.500 in in standard 12-ft lengths. Sheet stock in 24 x 48 in and 36 x 96 in sizes is available in thicknesses from 0.016 to 0.250 in. C110 round bar in diameters from 0.250 to 3.0 in and tube in standard plumbing sizes are also generally in stock. Tellurium copper C145 round bar in diameters from 0.250 to 2.0 in is stocked at specialty copper distributors in the region but may require 1–2 week lead time for less common sizes. C101 OFHC is a special-order item with 2–4 week lead time from regional distributors. For all copper grades, verify conductor certification (ASTM B187 for bus bar) versus structural grade (ASTM B152 for sheet) when electrical conductivity documentation is required by the program.
Copper bus bars for defense vehicle primary power distribution must be designed to carry continuous current without exceeding a temperature rise that would degrade insulation, reduce conductivity through annealing, or create thermal expansion problems at bolted joints. The standard design allowable for copper bus bars in enclosed enclosures is approximately 1,000 A/in² of cross-section for continuous 30°C rise above ambient — meaning a 0.25 in x 1.0 in bar (0.25 in² cross-section) handles approximately 250A continuously. For intermittent or peak loads, higher current density is acceptable with appropriate thermal analysis. Silver plating of contact surfaces at bolted joints (per MIL-DTL-45204 for defense programs) prevents oxidation and maintains low contact resistance over the life of the vehicle — unplated copper joints oxidize rapidly and their contact resistance climbs, causing voltage drop and localized heating. Specify 0.0001 to 0.0003 in electroless or electrolytic silver plate over copper at all contact surfaces, with no silver over the areas to be bolted together (which would otherwise cause galling).
For tellurium copper C145 in CNC turning and milling, Fox Valley job shops can consistently hold ±0.001 in on bore diameters, ±0.002 in on milled features, and surface roughness of Ra 63 µin or better on turned ODs with appropriate tooling. The key process requirement is sharp, high-positive-rake carbide tooling with polished flute surfaces — standard tooling used for steel will produce built-up edge on pure or near-pure copper and inconsistent dimensions. For pure copper C110, the same dimensional tolerances are achievable but require additional care: slower feeds, very sharp tooling, and in-process measurement after each finishing pass to compensate for springback. Electroless plating dimensional allowance should be factored into pre-plate dimensions — 0.0001 in per side silver plate adds 0.0002 in to a bore diameter, which must be taken out of the pre-plate machining tolerance budget.

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Last updated: July 2026

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