What is the salt spray test standard for cables? For which environments?
Main standards: IEC 60068-2-11 (salt mist) or ASTM B117. Conditions: 5% NaCl, 35°C, continuous spray 48–720 h.
Applications: marine, offshore, coastal outdoor, automotive underbody.
Pass criteria: sheath no cracks, metal shield no severe corrosion, insulation resistance not significantly reduced.
What are cable ageing test methods? How to estimate remaining life?
- Air oven ageing (IEC 60811-401): 100°C, 7-10 days, elongation retention ≥50%.
- Thermal endurance (IEC 60216): accelerate at multiple temps, Arrhenius extrapolation to operating temp.
- Oxygen bomb ageing (UL 1581 § 48): for rubber cables.
Remaining life estimated via tensile strength, elongation, resistivity changes.
How does cable capacitance affect signal transmission?
Capacitance (nF/km or pF/m) affects:
- Slower rise time: high capacitance slows edges.
- Maximum distance: higher capacitance reduces achievable length.
- Power consumption: increases charging current.
Typical values: coax 50-100 pF/m; RS-485 twisted pair <50 pF/m. Test per IEC 61196-1-104 or IEC 60811-513.
What are NEXT and FEXT in cables?
NEXT: interference from a transmitted signal measured at the same end on an adjacent pair. Higher dB is better.
FEXT: interference from a transmitted signal measured at the far end.
Derived parameters: PSNEXT, ACR (Attenuation-to-Crosstalk Ratio = NEXT – Attenuation).
For balanced twisted pair (Ethernet). Standards: TIA-568-C.2, IEC 61156-5.
How to calculate cable attenuation? Relationship with frequency?
Attenuation α (dB/100m) = 10 × log₁₀(P_in / P_out).
Frequency dependence: skin effect & dielectric loss increase α at high frequency; α ∝ √f (conductor) + f × dielectric. Standards:
- Coax: IEC 61196-1-111
- Ethernet (Cat5e/6): TIA-568 specifies max attenuation at 1-100/250 MHz.
Source: IEC 61196-1-111 & TIA-568.
How to measure dielectric strength of a cable? What are the standard test voltages?
Method: Apply power-frequency AC (50/60Hz) between conductor and shield/water bath for 1 or 5 min. No breakdown.
Typical values (IEC 60227):
- 300/500V cable: 2.0 kV AC
- 450/750V cable: 2.5 kV AC
- UL cables: 1.5 kV or higher after VW-1.
DC test also allowed (DC ≈ 1.414 × AC).
Source: IEC 60227 & UL 1581.
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