C28000 is one of the few copper alloys that earns its place in two completely different duties at once: current-carrying components in electrical wiring systems, and pipework that carries water, steam or process fluid. The 60/40 copper-zinc balance gives the alloy useful conductivity, enough strength to hold threads and compression joints, and corrosion resistance that stands up to fresh water and marine air.
Why C28000 Appears in Electrical Components
Electrical fittings need a metal that conducts, machines easily, resists atmospheric corrosion and keeps a reliable clamping force over years of thermal cycling. C28000 provides all four: terminals, connector bodies, wiring accessories, earthing clamps, conduit fittings and switchgear parts are routinely machined or formed from it. The beta phase provides the strength that pure copper lacks, so a compression terminal made from this alloy does not deform permanently when the screw is tightened.
Electrical and Thermal Behaviour
| Property | Value |
|---|---|
| Electrical conductivity (annealed) | about 28 % IACS |
| Thermal conductivity | about 120 W/(m·K) |
| Density | 8.39 g/cm³ (0.303 lb/in³) |
| Melting range | approximately 900 – 940 °C |
| Modulus of elasticity | about 103 GPa |
| Magnetic behaviour | Non-magnetic |
Conductivity of about 28 % IACS is well below that of a high-conductivity copper grade, so the alloy is selected for current-carrying parts by design current density rather than by convenience. For a busbar or a heavy current path, the cross-section is calculated from the allowable temperature rise of the assembly, and a dedicated high-conductivity copper is used where the section would otherwise become impractical. Where a part only carries the current of a control circuit, C28000 is a sound choice: it holds threads, resists corrosion and machines at high output.
Cold work raises strength and slightly reduces conductivity, so current-carrying parts are normally specified in an annealed or lightly worked temper when conductivity matters, and in a harder temper when clamping strength dominates.
Performance in Piping and Water Contact
In piping duty the alloy shows good resistance to fresh water, neutral and mildly alkaline solutions and marine atmospheres, and it tolerates the moderate flow velocities found in domestic and industrial water systems. Its strength allows thinner walls than a low-strength copper grade for the same pressure rating, and its machinability makes it economical for fittings with threads, flanges and sealing faces.
Water chemistry: the alloy performs best in neutral to slightly alkaline water; strongly acidic or highly aerated soft water accelerates attack.
Flow velocity: keep velocity within the range recommended for the piping system to avoid impingement and erosion-corrosion.
Temperature: service temperatures well below the melting range are used; high-temperature steam service is normally assigned to a copper grade with different alloying.
Joints: soldered, brazed, threaded and compression joints are all common, with brazed joints preferred for higher temperature pipework.
Dezincification and Stress Corrosion
Two selective-corrosion mechanisms govern the long-term performance of any high-zinc brass, and both belong in the technical review:
Dezincification: in aggressive chloride-bearing waters the zinc can be leached preferentially from the alloy, leaving a porous copper-rich residue. Resistivity of the alloy to this mechanism is assessed with the ISO 6509 dezincification test, and where the water is known to be aggressive a grade with a dezincification inhibitor addition is specified instead.
Stress corrosion cracking: residual stress from cold work plus exposure to ammonia or ammonium compounds causes cracking. The ASTM B858 ammonia vapour test and the ASTM B154 mercurous nitrate test are the recognised ways to verify that a delivered lot is adequately stress relieved, and a low-temperature stress-relief anneal of the finished part removes the risk.
Selection and Installation Notes
State the product form and standard: drawn bar, tube, strip or fittings, each with its own specification.
Declare the temper, because conductivity, strength and stress-corrosion behaviour all follow the temper line.
Require a certificate of analysis and a stress-relief statement where the part carries residual stress from machining.
Avoid mixing the alloy with more noble metals in a wet assembly, since galvanic effects concentrate at the joint.
Protect stored fittings from ammonia-bearing atmospheres such as cleaning agents and animal waste.
FAQ
Q: Is C28000 a good electrical conductor?
It conducts at roughly 28 % IACS, which is adequate for terminals and control-circuit parts but well below high-conductivity copper used for heavy current paths.
Q: Can C28000 be used for water pipe?
Yes, for fresh water and moderately aggressive industrial water, provided velocity and water chemistry stay inside the recommended range for the alloy.
Q: What is dezincification?
It is the selective leaching of zinc from a copper-zinc alloy in aggressive water, leaving a weak porous copper layer; ISO 6509 is the standard test used to assess resistance.
Q: How is stress corrosion cracking avoided?
By stress-relief annealing after cold work or machining and by avoiding ammonia and ammonium exposure in service and storage.
Q: Does plating affect conductivity?
Tin or nickel plating adds a small contact resistance but improves corrosion resistance; the effect is evaluated for signal-level parts rather than power paths.
Q: Why choose brass instead of copper for pipe fittings?
Because the alloy machines faster, holds threads better and offers higher strength for the same wall thickness while still resisting water-side corrosion.
