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Many technical terms describe the electrical characteristics of cables and wires in the wire and cable industry. However, these are terms that you will be forced to learn regardless of whether you ever get into the world of wires and cables. So here is a short overview of some essential electrical characteristics terminology in the wire and cable industry:
Spark Test
Used to check Insulation defects on an insulated conductor. It is usually done with a spark tester during the core eruption or stranding process. It can be used during the complete stranding process as well. In practice, cables with shields (e.g., braided wire and aluminum foil outside) use a spark tester to detect failures during the extrusion of the outer sheath. This is a fundamentally simple means of applying voltage between the electrode that touches the object to be tested and the ground conductor. A breakdown can also occur in this insulation medium (e.g., a turn that is too thin or completely missing), where the voltage applied will lead to an arc on the grounding conductor. It will fire the connected indicator (buzzer, light, counter, etc.)
The spark test is based on high voltage, and the equipment should be thoroughly grounded. The testator can employ an AC or DC voltage and typically uses an AC voltage at various frequencies. The testing current is often kept at lower deadlines to minimize risk.
Conductor Continuity
One of these key characteristics is the conductor continuity of wires and cables. Continuity tests shall be carried out at no more than 100V DC except as part of the functional tests. Manual Continuity Testing: Using a 9V battery hooked up in series with a visual or audible indicator. Remove the insulation at both ends of your conductor. Separate the conductors. Use an automatic (tester) to adjust the conductors one step at a time onto 1. However, when manual testing is used, each conductor on one end is often contacted with the same test terminal and voltage (not current) is detected at both ends. Bi-color, i.e., RED and GREEN LED indicators, to show whether the circuit under test is continuous or open.
Conductor Resistance
Resistance is an essential feature of each conductor in a wire or cable.” The conductor resistance measurement is still used only as a sampling check during the end-of-line tests (per unit-miles when shipped [ex, reel]). This property can then be sampled during measurement if the cable comprises a massive conductor. Conductor resistance measurements are performed at 68°F (20°C) unless otherwise stated. The test for Temperature coefficient is as per ASTM B 193. The resistance is dependent on the length of the cable. The conductor resistance is generally determined with a voltmeter/ohmmeter or a Wheatstone bridge.
Conductor Resistance Unbalance
The resistance difference between any pair of conductors is critical in communication transmission. Unbalanced conductor resistance is usually measured simultaneously with conductor resistance measurement. The resistance values are recorded per pair. The absolute difference between the maximum and minimum resistance is the absolute resistance imbalance per pair. Absolute resistance imbalance is usually expressed as Ω/1000ft or Ω/km. A more commonly used representation is as follows:
Unbalance Resistance = (Maximum Resistance – Minimum Resistance) / Minimum Resistance x 100%
Coaxial Capacitance (Capacitance To Water)
During manufacturing, water capacitance is measured by immersing the insulated conductor in a tank, measuring the capacitance between the ground conductor and water, and automatically feeding it back to the control equipment. Coaxial capacitance is between a circular metal conductor’s outer surface and the insulation layer’s outer surface. The test method is to immerse a section of the insulated wire in a water tank. Measure the capacitance directly between the ground conductor and water, with water temperature generally at 20°C ± 2°C and frequency at 1000 ± 10 Hz.
Mutual Capacitance
Mutual capacitance refers to the effective capacitance between a pair of conductors. In a multi-conductor cable, the mutual capacitance formula is as follows:
Cm = Cab + (Cag)(Cbg)/(Cag + Cbg)
Before measuring, strip the outer sheath, shielding layer, etc., at both ends of the cable until about 2 feet of the core wires are exposed. Separate the conductors at one end of the cable. Ensure that the conductors are not short-circuited or grounded. After stripping the insulation layer of the conductors at the other end of the cable, short all conductors, then connect to the ground for measurement. Unless otherwise specified, mutual capacitance refers to the capacitance at an AC frequency of 1000 ± 100 Hz.
Capacitance Unbalance – (Pair To Ground)
Capacitance unbalance to the ground is shown in the following figure.
A and B are a pair of conductors. Cag and Cbg are the shield’s direct capacitance between conductors A and B. Cap and Cbp are the direct capacitance between conductors A and B and other pairs of conductors. The formula is:
Cupg = (Cap + Cag) – (Cbp + Cbg)
Attenuation
Attenuation refers to the loss of signal strength as the signal passes through a wire or cable. It is influenced by the insulation conductor material and geometric shape, with units in decibels (dB). The concept and definition of dB values (decibels) are based on energy or power, where power equals the time derivative of energy or the energy output per unit time.
Propagation Delay
Propagation delay refers to the time it takes for a signal to pass through the measured object. The smaller the dielectric constant, the faster the propagation speed and the smaller the loss.
Velocity of Propagation
The velocity of propagation, also known as the velocity of the waveguide (one of the characteristics of a coaxial cable), is defined as the square root of the product of the dielectric constant in vacuum and the dielectric constant of the insulating medium. Since the dielectric constant in a vacuum is 1, it is expressed as follows:
The ratio of the signal propagation speed in a cable to the propagation speed in free space. The dielectric constants of various materials with air are as follows:
Cross Talk
It occurs when adjacent conductors interfere with each other during signal transmission. The common types of crosstalk are:
NearCrosstalkstalk (NEXT)
Power Sum Near-End Cross Talk (PSNEXT)
Equal Lever Far-End Cross Talk (ELFEXT)
Power Sum Equal Lever Far End Cross Talk (PSELFEXT)
Structural Return Loss (SRL)
SRL is derived from the input impedance (square root of open/short circuit impedance), while RL is derived from the termination impedance scanning. SRL compares the input impedance to the characteristic impedance, while RL compares the termination impedance to the load impedance (e.g., 100Ω), so these two measurements differ. Independent characteristic impedance and SRL characteristic curves are usually the preferred methods in the specification. This is because the two curves can be easily distinguished. From a measurement standpoint, the RL method is sometimes preferable because it does not require an input impedance function but uses the load impedance as a reference value.
Impedance
It is the sum of resistance, capacitance, and impedance in a specific AC circuit, with units in ohms (Ω).
It is expressed as Z = R2 + (XL-XC)2, where Z is impedance, R is resistance, XL is inductive reactance, and XC is capacitive. The common types are:
- Input Impedance
- Characteristic Impedance
There are two test methods for input impedance
Open/Short Method
The basic principle of the open/short measurement method is as follows:
A network analyzer will be used for testing, and the actual open/short data will be input into the above formula to calculate the input impedance.
Matched Load Method
The basic principle of the matched load measurement method is as follows:
Connect a load matching the impedance of the wire to be tested at the end of the test line, use a network analyzer for testing, and the instrument will automatically calculate the input impedance based on the formula above.
Sam Wu is the Marketing Manager at Romtronic, holding a degree in Mechatronics. With 12 years of experience in sales within the electronic wiring harness industry, he manages marketing efforts across Europe. An expert in cable assembly, wiring harnesses, and advanced connectivity solutions, Sam simplifies complex technologies, offering clear, actionable advice to help you confidently navigate your electrical projects.
