faq

• Q

  What is characteristic impedance of a cable? How to calculate? Effect on signal transmission?

  A

  Definition: Z₀ = √(L/C), L=inductance/m, C=capacitance/m.
  Typical values: coax 50Ω (RF) or 75Ω (video); RS-485 twisted pair 120Ω.
  Effect: mismatch causes reflections, signal loss, high BER.
  Test standards: IEC 61196-1-108 (coax); TIA-568 (Ethernet).

• Q

  How to convert AWG to mm²? Is there a common reference table?

  A

  Approx conversion: area(mm²) = 0.012668 × 92⁽³⁶⁻ᴬʷᴳ⁾/¹⁹
  Typical values:

  AWG	mm² (copper)	Approx ampacity (A)
  30	0.05	0.5
  28	0.08	0.8
  26	0.13	1.3
  24	0.20	2.1
  22	0.33	3.5
  20	0.52	5.5
  18	0.82	8.5
  16	1.31	13.5
  14	2.08	20
  12	3.31	30
  10	5.26	45

  Per ASTM B258 & UL 1581.

• Q

  Differences between tinned, silver-plated and nickel-plated conductors? When to use each?

  A

  Plating	Temp rating	Corrosion resistance	Solderability	Typical use
  Tinned	150°C	moderate	good	general electronics, automotive
  Silver	200°C	poor (tarnishes)	excellent	high frequency, high temp
  Nickel	260°C	excellent	fair	high temp, oil, marine

  Per IEC 60228 annex.

• Q

  How to select oil-resistant cables? What are the standards?

  A

  Based on oil type:

  - Mineral oil: per EN 60811-404 (IRM 902, 100°C, 72h)

  - Vegetable/synthetic oil: per EN 60811-405 (IRM 903)

  - Oil-resistance marking: “O” mark, e.g., UL 1277 oil immersion test.

  Typical materials: TPU, CPE, NBR/PVC blends.

  Source: EN 60811-404/405 & UL 1277.

• Q

  What is cable fire resistance? How does it differ from flame retardancy?

  A

  Flame retardant: prevents flame spread, tested per IEC 60332.
  Fire resistance: maintains circuit integrity during fire, tested per IEC 60331 (750°C, 90 min) or BS 6387 (950°C, 3h).
  Used for fire alarms, emergency lighting, evacuation systems.

  Source: IEC 60331 & BS 6387.

• Q

  Should cable shield be grounded at both ends or one end?

  A

  Depends on frequency and interference type:

  - Low frequency (<1 kHz) or electrostatic shield: ground at one end (avoid ground loop).

  - High frequency (>1 kHz) or EMI shield: ground at both ends (lower shield impedance).

  - Instrumentation/RS-485: typically single-end ground, connect only to signal ground.

  Reference: IEC 61000-5-2 & EMC practices.