It is very simple to find length of the conductor – to measure it enough. However, if the conductor is inaccessible or has very big length, then its direct measurement can be very difficult.

## It is required to you

- - construction roulette;
- - ampermeter (tester);
- - caliper;
- - table of conductivity of metals.

## Instruction

1. To find length **of the conductor**, measure by a roulette of length of its certain sites and put them. This method is suitable for an open electrical wiring and measurements of a wire in temporary cable connections.

2. If an electrical wiring hidden, then for finding of exact length of the conductor use the corresponding wiring scheme. If that scheme is absent, then try to restore indirectly placement of wires by position of sockets, switches, junction boxes, etc. to signs.

3. Consider the important rule of construction electricians: all wires have to be laid strictly horizontally or vertically. And, horizontal sites of a wire, as a rule, pass along the upper edge of a wall (under a ceiling). However, only the special device or the experienced electrician will be able to define the valid arrangement of wires.

4. If it is impossible to restore a trajectory of the hidden electrical wiring, then measure the electrical resistance of certain sites of the conductor. For calculations specify also the section of a wire and material of which it consists. As a rule, it is copper or aluminum. As a formula for calculation of resistance: R = ρ * L * s, length of the conductor it is possible to calculate by a formula: L = R / ρs, where: L – length of the conductor, R is resistance of the conductor, ρ – the specific resistance of material of which the conductor, s – the cross-sectional area of the conductor is made.

5. When calculating length of the conductor consider the following parameters and ratios. Specific resistance of a copper wire is 0.0154 - 0.0174 ohms, aluminum: 0.0262 - 0.0278 ohms. (If length of the conductor is equal to 1 meter, and section – 1 mm²). Section of the conductor equals: s = π/4 * D², where: π - number "пи", approximately equal 3.14,D – diameter of a wire (which is easy for measuring a caliper).

6. If the wire is winded in the coil, then determine length of one round and increase by quantity of rounds. If the coil has round section, then measure diameter of the coil (average diameter of a winding if it multilayered). Then increase diameter by number "пи" and by quantity of rounds: L = d * π * n, where: d – diameter of the coil, n is quantity of rounds of a wire.