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Introduction. Two Cables, Two Worlds
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High-Frequency
Cables
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High-Current Cables
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Signals: from MHz to 100 GHz.
Design pillars:impedance
matching,loss
control and shielding.
Applications: 5G, mmWave radar, PCIe Gen5/6, 224G Ethernet,
SATA, HDMI, USB4.
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Currents: from tens of amps to
thousands.
Design pillars:cross-section,thermal endurance and voltage-drop
management.
Applications: EVs, energy storage,
solar PV, industrial automation, rail transit, marine and aerospace.
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In summary: a high-frequency cable is a "highway for waves"— flat, impedance-continuous, reflection-free. A high-current cable is a "pipe for energy"— large diameter, low resistance, good heat dissipation.
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What
high-frequency cables care about
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What high-current cables care
about
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Whether the signal wave arrives intact
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Whether the energy is delivered loss lessly
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Whether the impedance is
matched (otherwise energy reflects)
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Whether the resistance is low enough (so it doesn't heat up)
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Whether high-frequency loss is
tamed (skin effect)
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Whether the voltage drop stays within the load's tolerance (V
= IR)
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Whether outside noise is
blocked (shielding)
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Whether the insulation survives the temperature and voltage
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01 / High-Frequency. Signal Highways from MHz to 100 GHz
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From
4G/5G, Wi-Fi, USB, HDMI, SATA and PCIe to automotive radar, satellite links
and defense systems — whenever the signal wavelength approaches the physical
size of the cable, you are in high-frequency territory.
1.1 The Frequency Spectrum
Each frequency band calls for a different cable technology. Once the wavelength gets close to the cable's physical dimensions, the skin effect and dielectric loss start to dominate the design.
As frequency rises, wavelength shrinks. Once it approached the cable's geometry, transmission-line behavior kicks in.
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1.2 Six Core
Electrical Parameters
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Open any high-frequency cable datasheet and these six parameters will jump
out. They decide whether the signal gets through intact.
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① Characteristic Impedance
Z₀= √(L/C). Common values: 50Ω
(RF), 75Ω (video), 90Ω (USB), 100Ω (Ethernet). Source, cable and load must
agree — otherwise energy reflects back.
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④ VSWR
Voltage
Standing Wave Ratio. VSWR = 1 is perfect match; mobile-antenna feed systems
typically require< 1.5.
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② Insertion Loss
IL= signal attenuation in dB
per unit length. It rises with frequency. Shorter length, lower-loss
dielectric and larger conductor all help.
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⑤ Skew
Propagation-time
difference between the two wires of a differential pair (ps/m). High-speed
serial links (PCIe, USB, HDMI) are highly sensitive to skew — too much
collapses the eye diagram.
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③ Return Loss
RL= the dB ratio of reflected power to incident power,
caused by impedance mismatch. Higher is better — >10 dB is acceptable,
>20 dB is excellent.
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⑥ Crosstalk
Electromagnetic
coupling between adjacent pairs (NEXTnear-end /FEXTfar-end, in dB). Twisting and shielding are the main
countermeasures.
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1.3 Common Characteristic Impedances
Why exactly 50 ohm? It's the engineering compromise between maximum power transfer and minimum loss.
1.4 Cross-Section of Coaxial Cable
The coaxial is the archetype of high-frequency cables. Four layers, inner to outer - each one shapes how the electromagnetic field propagates.
Skin effect: above 1MHz, current only flows the surface of the conductor. That's why high frequency conductors are often silver-plated and why mmWave use a hollow tube or Litz wire instead.
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1.5 Four
Mainstream High-Frequency Cable Types
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By
signalling method and structure, the major families are:
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Type
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Typical Z₀ /
Frequency
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Main Applications
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Key Properties
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Coaxial
(RG58 / RG174 / semi-rigid)
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50Ω /
75Ω · DC–110 GHz
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RF
antenna feeds, test instruments, semi-rigid in mmWave radar modules
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Single-ended,
excellent shielding, limited bend radius
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Twinaxial (Twinax)
(SATA / PCIe direct-attach)
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85Ω /
100Ω · 25 Gbps+
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SATA,
PCIe, SAS, internal high-speed server links
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Two
differential wires under a shared shield — more compact than coax
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Twisted Pair
(Cat5e / 6 / 6A / 7 / 8)
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100Ω ·
1–40 GHz (Cat8)
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Ethernet
(10G/25G/40G/100G), industrial Profinet
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Twisting
cancels common-mode noise; Cat7/8 add overall shield (S/FTP)
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Ribbon / FPC
(FFC / FPC with GND)
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90Ω /
100Ω · ≤ 16 Gbps
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Laptop
displays, board-to-board (B2B) inside a chassis
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Parallel
runs cause skew — needs length matching and proper grounding
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1.6 Main Application Areas
02 / High-Current Cable. Energy Hauling from 10 A to 1000 A
From a home EV charger (32 A) and an automotive BMS bus (200 A) to solar storage (300 A+) and rail traction (thousands of amps) — the design of a high-current cable revolves around cross-section, thermal endurance, voltage drop and mechanical strength.
2.1 The Current Scale
Each current level maps to a different conductor cross-section and cooling strategy. Doubling the section halves the resistance and quarters the heat.
Each 10x bump in current needs roughly 10x cross-section to hold the same temperature rise.
2.2 Six Core Parameters
Where high-frequency cables worry about the wave, high-current cables worry about heat and voltage drop.
① Ampacity The
maximum current a cable can carry continuously under rated conditions. Driven
by cross-section, insulation temperature rating and installation method (free
air / conduit / buried).
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④ Conductor Resistance In Ω/km. Copper 1.72×10⁻⁸ Ω·m, aluminium 2.65×10⁻⁸ (≈ 1.6×
copper) — so an aluminium cable needs~1.6×
the cross-section to match copper's ampacity.
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② Voltage Drop V
= I × R × L. Low-voltage systems typically require
< 3% (lighting) or < 5% (power). Longer runs and higher currents both
demand a thicker conductor.
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⑤ Withstand Voltage The maximum voltage the insulation tolerates to ground or
phase-to-phase. Common: 300/500 V (electronics), 0.6/1 kV (power), 6/10 kV
(medium voltage), 26/35 kV (high voltage).
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③ Temperature Rating The rated operating temperature of the insulation: PVC 60–105°C, XLPE 90°C, Silicone
180°C, PTFE 200°C, ETFE 150°C. Higher rating = more ampacity.
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⑥ Flame / Safety VW-1,FT1/FT2,FT4,IEC 60332-3. Automotive UL 758,
storage UL 1973, EV charging IEC 62893 / 62196.
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2.3 Cross-Section v.s Ampacity
Approximate values for copper conductor XLPE 90 degree Celsius insulation, single-core, in free air.
Bigger section means more current but also more weight, more cost and harder installation.
2.4 Cross-Section of a High-Current Cable
Why not just use a solid copper bar? Besides flexibility, a standard bundle actually exploits the skin effect; under high-frequency or pulse DC(PWM) conditions, current travels on the surface of every fine strand, so the effective cross-section is larger than a solid conductor of the same diameter. That's why the Litz wire is also popular in high-current applications.
2.5 Six Mainstream High-Current Cable Types
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Type
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Typical Current / Voltage
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Main Applications
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Key Properties
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Power Cable
(THHN / XLPE / NM-B)
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10–500 A · 0.6/1 kV
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Building distribution, industrial panels, solar
DC
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Single or multi-core; copper most common,
aluminium also used
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Welding Cable
(H01N2-D / 60245 IEC 81)
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200–600 A · 100 V
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Welding machines, temporary high-current
grounding
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Ultra-flexible Class 6 strands, abrasion- and
heat-resistant rubber jacket
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Battery Cable
(SGX / SGT / WBK)
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50–300 A · 60 V DC
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Automotive, EV, UPS, energy storage systems
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Oil- and chemical-resistant, ultra-flexible,
vibration-fatigue resistant
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Silicone High-Temp Wire
(UL 3135 / 3239 / 3530)
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5–100 A · 600 V
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Heaters, motor leads, inside solar inverters
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−60°C to 200°C, flame-retardant, flexible
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EV Charging Cable
(IEC 62893 / GB/T 33594)
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16–250 A · 450/750 V AC
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AC slow charging, DC fast charging, portable EVSE
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High-flex TPE jacket + integrated signal/control
cores
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Busbar
(Cu / Al bar with heat-shrink)
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400–3000
A · 1 kV+
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Switch gear,
data centers, rail traction
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Flat
copper bar + heat-shrink insulation; replaces very large cables
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2.6 Main Application Areas
03 / Side by Side. The Two Cables at a Glance
This is where beginners most often get confused. The key difference to remember: high-frequency cares about the wave, high-current cares about the heat.
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Dimension
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High-Frequency Cable
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High-Current Cable
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Core
physics
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Voltage waveform, impedance,
loss
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Current, resistance, temperature
rise, voltage drop
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Frequency
/ current
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1 MHz – 100 GHz (even THz)
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DC – low frequency; 10 A – 3000 A+
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Primary
design goal
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Signal integrity (SI), impedance
matching, EMI rejection
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Low voltage drop, low heat,
thermal endurance, mechanical strength
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Key
parameters
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Z₀, IL, RL, VSWR, Skew,
Crosstalk
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Ampacity, V drop, Temp Rating,
Withstand Voltage
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Conductor
preference
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Solid or 7-strand,
silver-plated, copper-clad steel; large surface area
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Many fine strands (Class 5/6);
bigger and bigger as current rises
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Insulation
material
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Low Dk, low Df: PE / FEP / PTFE
/ foam PE
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Heat-resistant, flame-retardant:
XLPE / PVC / Silicone / TPE
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Shielding
importance
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Critical (double braid + foil,
S/FTP, overall shield)
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Depends — only required when mixed
with signal; pure power cables often skip it
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Failure
mode
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Reflection, signal distortion,
eye-diagram collapse, EMI over-spec
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Burning, fire, excessive voltage
drop, insulation breakdown
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Main
standards
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USB-IF, PCI-SIG, IEEE 802, IEC
61156
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NEC (NFPA 70), IEC 60364, UL 758,
GB 50054
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Selection
keywords
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Bandwidth GHz, impedance Ω,
dB/m, ps skew
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Section mm², current A,
temperature °C, voltage V
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