Cable & Wire Technical Characteristics
A: The capacitance (C) of a component – in this case a cable – represents its ability to store electrical energy. A cable with low capacitance can be used over longer distances and offers lower transmission losses than a standard cable of the same length.
Whether or not a cable qualifies as "low-capacitance" depends on the insulation material that is used. In the field of data network cables, pure air would be one of the best and thus also one of the lowest capacity insulation materials. However, since it is technically impossible to use air as core insulation and to strand the bare copper conductors without contact, a range of different plastics are used for insulation purposes. Air has a dielectric constant of 1. Similarly, all insulation plastics used in cable technology also have a specific dielectric constant, which is measured at a specified frequency and ambient temperature. The dielectric constant indicates the factor by which the capacitance increases when air is replaced with a different insulation material such as polyvinyl chloride (PVC) or polyethylene (PE). The higher the dielectric constant, the greater the capacity. The lower the constant, the better suited the material is to electrical core insulation. Compared to other insulation materials, PE for instance has a very low dielectric constant of approx. 2.2, which is why it is used for higher quality products such as LAN, BUS or coaxial cables. In some cases, small air bubbles or foam are encapsulated in the PE insulation to further improve the transfer quality. Depending on its composition, PVC takes up a mid-table position with values between 3.5 and 7. With dielectric constants of up to 9.0, elastomers such as chloroprene rubber are at the bottom of the pile when it comes to insulation materials for data network cables; even when used for connecting or control cables, relatively thick insulation wall thicknesses of such materials are required to achieve satisfactory insulation performance. Symmetrical core stranding can also have a positive effect on the capacitance (e.g. ÖLFLEX® SERVO 9YSLCY-JB with its three-part, green/yellow protective earth conductor).
A cable can be described as "low-capacitance" if the mutual capacitance specified in the catalogue for a PE-insulated cable, for example, is approx. half that of a cable which merely has PVC insulation, for instance.
UNITRONIC® FD (PVC-insulated) = mutual capacitance 140 nF/km
UNITRONIC® FD P plus (PP-insulated) = mutual capacitance 60 nF/km (thus qualifying as low-capacitance)
The electrical capacitance is measured in Farad (F).
A: The rated voltage of a cable is the voltage on which the construction and testing of the cable is based in the context of electrical inspections. It is specified in the form of two voltage values: U0/U.
Many ÖLFLEX® connection and control cables have a rated voltage of U0/U 300/500 V.
• U0 is the rms-value (root mean square) of the voltage between a live conductor (core) and the earth (ground).
The earth can be a metallic cable sheath (copper braid) or an earthed surrounding medium such as the metal casing of a device or control cabinet.
The U0 value is lower than the U value, as there is as electrical separation only one layer of insulation between the live copper conductor and surrounding metallic medium.
• U is the rms-value of the voltage between 2 live conductors (cores) of a multicored cable or within a system of single cores.
The U value is higher than the U0 value since there are always as electrical separation two layers of insulation between two live copper conductors in a multi-core cable or between two single cores in a switch cabinet.
The electrical voltage is measured in Volt (V).
A: For virtually all of our ÖLFLEX® cables, the rated voltage is specified in the form of an AC value (Alternating Current). In a DC system (Direct Current), the rated voltage of the system must not be greater than 1.5 times of the rated voltage of the cable.
To calculate the DC value, the relevant AC value is simply multiplied by a factor of 1.5, as in the examples below:
AC Alternating current Factor DC Direct current
U0/U 300/500 V x 1.5 U0/U 450/750 V
U0/U 450/750 V x 1.5 U0/U 675/1125 V
U0/U 600/1000 V x 1.5 U0/U 900/1500 V
The electrical voltage is measured in Volt (V).
A: The current transfer raises the temperature of cables and wires on the basis of the current amperage or the selected conductor cross-section. If the current is too high, a cable installed in a room temperature of +20°C can easily reach a surface temperature of +80°C. If the ambient temperature were also to increase significantly, the maximum permissible conductor temperature of the cable would be greatly exceeded. This could result in damage to the core insulation material, the cable sheath and even the copper conductor, or cause the premature failure of these components.
Depending on the applicable standards, the various copper conductor cross-sections are all assigned maximum current ratings. The core insulation material plays little to no part here. What is important is how the cable is installed and whether it is a single core or multicore cable. In accordance with DIN VDE 0298, part 4, table 11 (see catalogue appendix table T12-1), the power rating values specified here apply to an ambient temperature of +30°C.
As per column B of table T12-1, the maximum continuous current that can be supplied to an ÖLFLEX® 450 P 3 G 1.5 cable for hand-held equipment at an ambient temperature of +30°C is 16 A per core (1.5 mm²).
If the ambient temperature rises to +50°C, for example, the so-called “correction resp. reduction factor" comes into play, the aim of which is to reduce the current load on the cable.
The reduction factor to be applied is derived from the prevailing ambient temperature and the maximum permissible conductor temperature of the cable. On the catalogue page for the ÖLFLEX® 450 P cable, the maximum permissible conductor temperature is specified as +70°C. Based on these two temperatures, the reduction factor 0.71 can be read from table T12-2 ("Correction factors") in the catalogue appendix; the maximum current rating is then multiplied by this factor.
If a customer wants to supply for his application a 16 A current to an ÖLFLEX® 450 P 3 G 1.5 mm² cable at an ambient temperature of +50°C, a conductor cross-section of 1.5 mm² will be insufficient!
ÖLFLEX® 450 P 3 G 1.5 mm²:
Max. load at +30°C as per table T12-1, column B: 16 A
Max. load at +50 ℃ as per table T12-2: 16 A x reduction factor 0.71 = 11.36 A
Result: To be able to conduct a 16 A current at an ambient temperature of +50°C, the conductor cross-section must be increased to a suitable size.
ÖLFLEX® 450 P 3 G 2.5 mm²:
Max. load at +30°C as per table T12-1, column B: 25 A
Max. load at +50 ℃ as per table T12-2: 25 A x reduction factor 0.71 = 17.75 A
Result: Increasing the conductor cross-section from 1.5 mm² to 2.5 mm² produces the required value of 16 A at an ambient temperature of +50°C.
Note that this calculation does not take account of other important factors for the correct determination of cable ampacity, e.g. the type of installation!
The amperage is measured in Ampere (A).
A: Although copper and steel are conductive metals, only copper (e.g. in the form of a braid) represents a suitable means of protecting a cable or wire from electromagnetic interference or shielding the environment from the interfering emissions originating from the cable itself. This not only depends on the electrical conductivity of the metal employed, but also on the braid density or the degree of coverage with which the cable is braided.
From all metals only pure silver offers marginally better conductive performance than copper. Although different qualities of iron/steel alloy exist, the conductivity of steel is generally six times lower than that of electrolyte copper. For this reason, a steel wire braid only ever protects a cable from external mechanical impact. To ensure optimized electromagnetic shielding, which also meets the requirements of the Electromagnetic Compatibility (EMC) directive, a sufficient level of copper braiding is required. As a minimum, a visual coverage level of 82-85% is required to achieve adequate screening protection. In the case of a steel wire braid used solely for mechanical protection, a visual coverage level of approx. 50% or less is standard. With a little practice, it is therefore quite easy to visually distinguish copper and steel wire braids by their degree of coverage. In addition, copper braids often have a slight reddish tinge (despite their tin plating), are somewhat softer than steel and are in comparison to steel non-magnetic.
However, even the densest, highest quality copper braid is rendered useless if it is not properly grounded! For safety reasons, steel wire braids should also be earthed when used in power networks. If the connected equipment develops a fault, this grounding prevents the transmission of dangerous voltages to the often exposed steel wire braid at the connecting points.
A: It is possible to measure the capacitance (C), inductance (L) and impedance (Z) on a cable drum or to calculate these values on the basis of specific key data. Calculations can be performed for virtually all ÖLFLEX® cables, but the values must be determined separately for each individual product article.
Calculations are only possible if the following data is known:
• Cable product and dimension
• Exact dielectric constant of core insulation material
• Diameter of copper conductor
• Wall thickness of core insulation
Accurate calculations are only possible if the relevant cable was produced in one of our own Lapp factories, meaning that all the above values are available.
The capacitance, inductance and impedance of many ÖLFLEX® products have already been established in the past and can be obtained on request from the PDC Technology department.
The electrical capacitance is measured in Farad (F).
The inductance is measured in Henry (H).
The impedance is measured in Ohm (Ω).
A: As a cable and wire manufacturer, we are not generally permitted to calculate the ampacity of cables for the planning or operation of electrical equipment, plants and systems. Such calculations usually involve many different factors, of which neither we nor – as is often the case – the customer are aware. If incorrect planning results in the selection of the wrong conductor cross-section, which in turn leads to faults, fire damage or personal injury during later operation of the machine or system, the party who conducted the planning will be held responsible! This is why a number of engineering consultancies make their living by planning electrical plants and systems.
The following are just some of the important factors required to ensure accurate and, most importantly, safe determination of the right conductor cross-section:
• What power level is to be transferred?
• What length of cable is to be installed?
• What is the ambient temperature where the cables are used?
• Are there any mechanical forces or chemical stressors affecting the cable?
• How are the cables installed? In pipes, open or closed cable ducts, cable conduits, on-wall or in-wall?
• How many cables are installed in the pipe, duct or conduit?
• How far apart are the cables in the conduit?
In some cases, we can provide reference values for advisory purposes. However, such data is always provided in a non-binding capacity and under consideration of the above points. It must also be pointed that full and adequate planning can only be performed by a recognized engineering consultancy. Written confirmations should not be provided!
A: No! This could easily result in fires or lethal electric shocks! Data network cables and power cables are subject to completely different design and test standards. The main difference lies in the core insulation strength. UNITRONIC® data cables are typically used in data networks with a voltage range of 6 to 48 V. ÖLFLEX® connection and control cables, on the other hand, are predominantly used for devices with a 230 V mains voltage (e.g. drills, lawnmowers etc.) or for machines in power or three-phase networks, e.g. U0/U 300/500 V or 600/1000 V.
Since the size of the voltage is directly connected to the strength of the core insulation, this represents the greatest difference between data and power cables.
To be able to cope with voltage ranges of U0/U 300/500 V, the core insulation of an ÖLFLEX® CLASSIC 100 power cable, for example, is on average 50-70% thicker than that of a UNITRONIC® LiYY data cable. It is possible for voltage peaks of 250 V to occur in data networks. However, under no circumstances must this voltage be equated with a stabilized alternating current of 230 V at 50 Hz supplied from a mains power socket! Using a data cable in this case would carry a very high risk of cable fires or electrocution resulting from the insufficient strength of the core insulation! The dielectric strength of data cables is generally only checked with 1200 to 1500 V for one minute periods. Connection and control cables, on the other hand, are tested with 4000 V for periods of 15 minutes.
Indirect connection of data cables to the power network is only possible if a transformer is used to convert the mains voltage to the permissible low voltage of the operated device (e.g. a laptop or model railway). In this case, it must be ensured that an ÖLFLEX® cable with the appropriate voltage class (e.g. U0/U 300/500 V) is used to connect the transformer to the mains supply and that the UNITRONIC® data cable is only used to link the relevant device with the transformer.
The electrical voltage is measured in Volt (V).
A: Heating systems, for example, require a relatively high voltage to ignite the pilot flame, but this is only needed once or twice a day and for a matter of milliseconds. Operators and users are often of the opinion that a cable with a rated voltage class of, for example, U0/U 300/500 V can be briefly supplied with a higher voltage, provided that it does not exceed the specified testing voltage. In such cases, it is very important to note that a cable with a rated voltage class of 300/500 V and a testing voltage of, for example, 4000 V must never be subjected a voltage exceeding the specified rated voltage – not even for a matter of milliseconds! Even if, for example, a voltage of 2500 V occurs just once per day for a single second, the relevant cable, and the core insulation thickness in particular, must be constructed and tested to ensure the appropriate rated voltage. In this particular case, a cable a with a rated voltage class of 1.8/3 kV must be used to safely handle the briefly occurring voltage of 2500 V.
The testing voltage listed for a specific product on the catalogue page, particularly in the case of ÖLFLEX® connection and control cables, in no way indicates that the relevant cable can be subjected to higher voltages – no matter how briefly.
The withstand or high voltage test is a required element of the final acceptance resp. inspection of each and every cable and only serves as a means of identifying any insulation faults after production.
A: Virtually all ÖLFLEX® connection and control cables are screened with tin-plated copper braiding. UNITRONIC® data cables are screened with copper braids and aluminum-laminated synthetic foils, which are generally wrapped around the core bundle in overlapping spirals. Some data cables, such as the UNITRONIC® Li2YCY PiMF or ETHERLINE® Cat.5, actually feature both an aluminum foil and an additional copper braid.
Copper braids primarily protect the cable against inductive coupling in the low frequency range in which virtually all connecting and control cables operate. If, for example, a UNITRONIC® data cable is installed in the direct vicinity of an ÖLFLEX® connecting cable that may not have copper screen braiding, the data cable should be protected against inductive interference from the connection cable by means of a screening braid. The same applies if a connecting cable is installed in the proximity of an insufficiently shielded or EMC-compliant machine or in the vicinity of an electric motor, which can also generate fields of inductive interference.
Aluminum foils are primarily used in data cables, as data is generally transferred at very high frequencies, thus necessitating protection against capacitive coupling.
The so-called coupling resistance and the transfer impedance act as indicators of the shielding performance – the lower the measured transfer impedance, the greater the effectiveness of the cable screening.
Of course, the best results are achieved by combining a foil shield with copper screen braiding. The disadvantage is that the aluminum foil laminate makes the cable quite stiff and inflexible, meaning that it is mostly only really suitable for fixed installations in conventional cable construction design. Frequent movement of the cable can quickly tear or displace the sensitive foil shield, which will have a negative impact on screening performance.