What “Class K” really means
If you’ve ever spec’d a flexible copper conductor and wondered, “Is Class K the right call, or should I use Class M?” this guide is for you. Let’s decode Class K in plain English and share a few practical tips to get your build right the first time.
The short version
Class K is a high-flexibility, fine-stranded copper conductor built from many small wires (typically 30 AWG strands) bunched or rope-layed together to reach your target gauge (e.g., 4 AWG, 2/0, 500 MCM). Compared to standard building-wire stranding (Class B/C), Class K bends tighter, tolerates vibration better, and routes through cramped spaces with less fight.
Why Class K exists (and where it shines)
Tight routing: Smaller bend radii for panel drops, battery/inverter jumpers, and equipment whips.
Vibration & motion: Fine stranding spreads strain and resists work-hardening in moving harnesses.
Faster install: Easier to pull, dress, and land in dense cabinets and trays.
Cleaner terminations: Plays nicely with crimp lugs designed for fine-strand conductors.
Common use cases: welding leads, flexible grounds, EV battery/inverter pigtails, robotics whips, control-panel jumpers, portable power, and generator sets.
Class K vs. Class M (and others)
Class B/C: Fewer, larger strands → stiffer, lower cost; good for fixed runs.
Class K: Many 30 AWG strands → flexible, widely available; the “workhorse” of flex.
Class M: Even finer (often 34 AWG strands) → maximum flexibility for severe motion; usually higher cost and slightly larger OD for the same ampacity.
Think of Class K as the sweet spot: much more flexible than building wire, more cost-effective and broadly stocked than ultra-fine alternatives.
What changes (and what doesn’t)
Electrical performance: For the same cross-section, DC resistance targets are comparable. Flexibility comes from strand count and strand size, not from sacrificing copper.
Outer diameter: Fine-strand constructions can run slightly larger OD due to air spaces between many strands, meaning your lug barrel and ferrule choice matters.
Terminations: Use lugs, dies, and crimp profiles rated for fine-strand. (When in doubt, ask us or your connector vendor for the correct barrel ID and crimp geometry.)
Spec’ing Class K like a pro
Ampacity & gauge: Start with the system current and temperature rise. We’ll help back-solve the gauge and lay to hit your target.
Finish:
Bare copper (BC) for general use.
Tinned copper (TC) for solderability and corrosion resistance.
Nickel-plated copper (NPC) for higher-temperature zones.
Lay & construction: Smooth-bunch or rope-lay to balance flexibility, OD, and roundness for your connectors.
Environment: Heat, oil/chemicals, salt, and motion cycles drive finish and strand choice.
Terminations: Pair with fine-strand-rated lugs/ferrules; confirm crimp tool and die code.
Put-ups: Tell us spool/reel size, cardboard basket preference, and target footage for your cells.