- - the cable cross-section with an unknown;
- - calipers or a micrometer;
- - Table resistivity substances.
Take the cable cross section you want to set.Most often, it consists of 2-4 strands are separated from each other special materials.These wires have the same diameter.Sometimes you can find cable, one core is thinner than the rest - it is intended for grounding.
Clean insulation from the cable core.Using vernier calipers, micrometer or better (this will produce a more accurate measurement), get the core diameter.Values obtained in millimeters.Then, calculate the cross-sectional area.To do this, multiply the factor 0.25 to the number and value of π≈3,14 diameter d squared S = 0,25
∙ π ∙ d².This value is to multiply the number of cable cores.Knowing the length of the wire, its cross section and the material from which it is made, calculate the resistance.
For example, if you want to find a cross-section of copper cable 4 conductors, and measuring the diameter of the conductor gave a value of 2 mm, get the cross-sectional area.To do this, calculate the cross-sectional area of one core.It will be equal to S = 0,25 ∙ 3,14 ∙ 2² = 3,14 mm².Then define the entire cross section of the cable cross-section of a conductor, multiply by the number in our example is 3,14 ∙ 4 = 12.56 mm².
Now you can find the maximum current that can flow through it, or its resistance, if we know the length.The maximum current for copper cable, calculate the ratio of 8 A 1 mm².Then the current limit, which can pass through the cable, take the example of 8 ∙ 12,56 = 100,5 A. Note that for an aluminum cable, the ratio is 5 A 1 mm².
example, the cable length is 200 m. In order to find its resistance, multiply the resistivity of copper ρ in Ohm ∙ mm² / m cable length l, and divide it by the cross-sectional area S (R= ρ ∙ l / S).Make the substitution, you get R = 0,0175 ∙ 200 / 12,56≈0,279 ohms, resulting in very low loss power transmission characteristics of this cable.
Tip 2: How to choose a cross-section of
When replacing wiring or connection of new lines you want to select an optimal cross section cable.Proper selection will provide trouble-free operation and reliability of the system, as well as the fire safety of the house.
- - calculation of the power consumption devices;
- - knowledge of the characteristics of the circuit breaker, fuse protection, etc.
At low current take-section cable m not less than 1 mm2 (for copper wire) or 2 mm2 (for aluminum conductors).
At large currents -section of the wire pick-link capacity.First, calculate, what power the appliance will be connected.The requirements of the device you can see in the documents or instructions for use.
If you need to calculate the cross-section of for the entire room or house, count all the devices that are in and which are planned to buy.Roughly estimate, how much equipment you can turn simultaneously in the busiest day (for example, in the new year or a wedding).Multiply the total load on the simultaneity factor, e.g., 70%.
Based on the calculation of capacity, according to which the load of 1 kW requires a 1.57 mm2 cross-section, calculate the cross sections for the particular wire.For example, for the aluminum conductor this value is 5 A per mm2, and for copper - 8 A per mm2.
Using the obtained values calculated wire cross section for your device.For example, if you want to install the water heater 5 kW, the wire should be selected such that it was designed by no less than 25 A. So you select the cross-section of copper wire m not less than 3.2 mm2.
Note that for aluminum wires -section should be selected higher, since their conductivity is about 62% compared with copper.For example, if you estimate that the load is suitable for the required wire cross-section m 2.5 mm2, the aluminum wire should be at least 4 mm2 and 4 mm2 copper wire corresponds to six-millimeter aluminum wire.
If possible, always choose the cable cross-section of more than came out of convenience.It is impossible to predict in advance, you suddenly decide to connect something else.Do not forget to check whether the design is consistent -section with a maximum actual load current with the circuit breaker or fuse protection, are usually near the counter.
- how to find cable cross