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So we want to select a cable to make sure that the voltage drop is not so large that it will cause problems, but what is acceptable and how do we calculate the right cable size to use? Well the generally acceptable voltage drop for DC circuits is around 3-4% and we can use V = IR (see Electrical Circuit Basics) to calculate the voltage drop for a cable if we know the current draw of the load and the cable's resistance per metre. Secondly, it has a greater working temperature range with a maximum of around 105ºC compared with around 70ºC for standard PVC. This makes it more suited to use in areas close to the engine. Expressed in mm² and describes the tota l cross sectional area of the copper conductor. You will sometimes see cable described as 1mm or 2mm cable without the ² sign but it is important to note that this does not mean the diameter of the cable. This can often lead to confusion so just remember that the main specification for a cable will be its conductor's cross-sectional area and cable will never be referred to by its diameter alone. Low voltage automotive and marine cable is available in different materials/constructions and the following table gives a brief overview: Material Each component or appliance connected to a circuit will have a current draw associated with its operation and it is important that the cable supplying power to these is capable of carrying the normally expected current, plus a margin of safety. If it is not capable then it is likely to result in the cable becoming hot and potentially catching fire. Although fuses are used in the circuit to protect the cable, the cable itself should be of an adequate rating to prevent this over-heating occurring under normal circumstances.
The number of devices connected to the circuit usually determines how much current will flow through the wire. This problem is overcome by manufacturing the core from many small diameter strands of copper wire to make up the desired cross-sectional area, rather than using a single wire. This type of cable is (unsurprisingly) known as 'stranded' cable and provides much more flexibility, which means improved resistance to work hardening making it better suited to use in vehicles. The difference in cross sections is shown in the diagram below: The table below provides a cross-reference between these two standards, showing the closest metric equivalents to each Gauge for cable sizes commonly used in low voltage automotive and marine applications. AWG In Europe, metric sizes are used for stranded cableand are expressed as the total cross sectional area of the conductors together with the number of strands and their diameter. For example, a cable specified as 2.0mm² 28/0.30 indicates that it has a total conductor cross sectional area of 2.0mm² and is made up of 28 individual strands, each of 0.3mm diameter. Input what percentage voltage drop is allowable. The smaller, the better, but the limit is 5% to keep devices working properly.In the US, the most commonly used wire gauge system is AWG, or American Wire Gauge. The higher the gauge number, the smaller the wire. In North America the AWG standard is most commonly used for stranded cable and expresses the Gauge together with the number of strands and their Gauge. For example, a cable specified as 16 AWG 7/24 has a size of 16AWG and is made up of 7 individual strands, each of 24 AWG. For more information regarding wiring and cables, see our comprehensive guide here. AWG Gauge Table AWG gauge
The AWG gauge system only applies for solid, round, non-ferrous conducting wires. Keep this in mind when evaluating wire size and type for your application, as AWG doesn’t apply to stranded or non-round wires. AWG Gauge Sizes for Home Wiring, Auto Wiring, and Boat Wiring In most situations the detrimental effects can be minimised by using shrink sleeving, sealed connectors, adhesive lined terminals, protective gels etc. to keep moisture out, but in some applications where the environment is particularly aggressive, for example marine use, it might be preferable to use cable with tinned conductors. This is simply where the standard plain copper conductor has has a layer of tin applied before being sheathed in the insulation.Tin doesn't react in the presence of moisture, yet retains good conductivity, and so improves long-term performance of the cable. The downsides are that it is slightly more expensive and there is a more limited range of sizes and colours available compared with plain copper. Earth braid straps that have no insulating layer are typically tinned for protection as a matter of course. Anyway, enough maths - to make it easy we've developed this handy calculator which will show you the approximate voltage drop based on cable size, supply voltage, current draw and cable length. All elements of an electrical circuit have resistance, including electrical cable, which means that there will be energy loss in the form of voltage drop experienced along the length of the cable. Just as a bulb converts electrical energy into heat and light due to its resistance, and so induces a voltage drop, a copper conductor has resistance and will convert some of the energy it conducts, causing a voltage drop in the same way. The difference is that voltage drop across a bulb (or other load) is useful as that's what makes it work, but voltage drop along cable and other passive parts of a circuit is not desirable as it's not a useful conversion of energy. The n gauge wire resistance R in ohms per kilofeet (Ω/kft) is equal to 0.3048×1000000000 times the wire's resistivity ρ in
AWG is also commonly used to specify body piercing jewelry sizes (especially smaller sizes), even when the material is not metallic. [2] Formulae [ edit ]
The n gauge wire resistance R in ohms per kilometer (Ω/km) is equal to 1000000000 times the wire's resistivity ρ inThe most common method of referring to conductor sizes uses the cross-sectional area, expressed in mm². The following AWG metric conversion table converts AWG to mm and inches, and also lists the cross sectional area (mm2). AWG Metric Conversion Chart (AWG to mm) The AWG tables are for a single, solid and round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.
The n gauge wire diameter d n in millimeters (mm) is equal to 0.127mm times 92 raised to the power of 36 minus gauge number n, divided by 39: Expressed as the number of conductors of a given diameter. So 28/0.30 means that there are 28 strands, each with a diameter of 0.30mm Input a value for the current of the system. This figure should be the peak current so that the cable can be sized for the worst case. This shows that 1.5mm² cable (at a current rating of 21A) will be suitable for the cable run length as the drop is well under 3% Change the temperature, if necessary. The value should be the maximum operating temperature that is expected for the wire.While the AWG is essentially identical to the Brown & Sharpe (B&S) sheet metal gauge, the B&S gauge was designed for use with sheet metals as its name suggests. These are functionally interchangeable but the use of B&S in relation to wire gauges, rather than sheet metal gauges, is technically improper. This shows that although 0.5mm² cable is OK for the expected current draw of the light, it's not OK for the cable run length as the drop is greater than 3%.
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