Conductor ampacity calculation formulas]

Related to the carrying capacity of the wire cross section of the wire, and conductor material, type, installation methods, as well as ambient temperature, the effects of many factors, calculations are more complex.

The ampacity of various conductors can usually find the manual. But the use of formulas together with a few simple mental arithmetic, can be directly calculated, and do not have to look-up table.

A formulas or aluminum conductor insulated wire contained multiple relationship of the flow cross-section

10 5, 100 on two

25, 35, four, three realms.

70,95, two and a half times.

Wearing a tube, temperature, and eight 10% off.

Bare wire plus half.

Copper upgrade count.

Description of formulas on the carrying capacity of the various cross-section of the (security) is not directly pointed out, but with a certain multiple of the cross-section multiplied. This end of commonly used conductors nominal cross section (mm2) is arranged as follows:

1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185 ......

(1) a formulas that the Lvxin insulated wire ampacity (A), according to multiples of the cross section to calculate. The formulas in the Arab digital wire cross section (mm2), the Chinese character numbers indicate multiples. The cross section formulas and multiple relationships lined up as follows:

1 to 10 16,25 35 50 70,95 120

>>>>}

Five times four times three times Two and a half twice

And formulas control is even more clear formulas "under 10 five" refers to the wire section 10, the wire ampacity section five times the values. 100 on "(read on) refers to the carrying capacity of wire cross-section 100 of the wire is twice the value of wire cross-section. Wire cross-section of 25 and 35 are four times and three times at the boundaries. This is the formulas 25, 35, four three realms ". The wire cross section 70,95, compared with 2.5 times. It can be seen from the above arrangement: In addition to the wire 10 and above 100 wire, the wire cross-section of the middle of each two specifications are the same multiples.

For example, Aluminum conductor, insulated wire, the ambient temperature of not more than 25 ° C wire ampacity calculation:

When the wire cross-section of 6 mm2, regarded as the carrying capacity of 30 safety;

When the wire cross-section of 150 mm2, be regarded as carrying capacity of 300 A;

When the wire cross-section of 70 mm2, can be considered the carrying capacity of 175 security;

Can also be seen from the above arrangement: multiples decreases with increasing cross-section, the change in the multiples of the junction, the error is slightly larger. Such as wire cross sections 25 and 35 are four times and three times at the boundaries, the wire 25 is four times the range, according to the formulas count as 100 A, but according to the manual for the 97 security; 35 On the contrary, according to the formulas count of 105 security , but the look-up table 117 A. However, this did not affect use. Of course, if a few chest, in the choice of conductive line section 25 does not make it full to 100 A, 35 can be slightly more than 105 safety will be more accurate. Similarly, 2.5 mm2 conductive line position in the five times the beginning of the actual will be more than five times (the maximum safety for more than 20), but in order to reduce the power loss within the wire, usually the current is not used so much in the manual is generally The standard 12 Ann.

(2) behind the three formulas is the processing conditions change. Wearing a tube temperature, 10% off: If wearing pipe laying (including the laying of the slot board, Traverse protective sleeve layer of unknown wires exposed), some calculation, call the discount for each purchase; if the ambient temperature more than 25 ℃, and then calculate the discount, both wearing pipe laying, the temperature is over 25 ° C, a discount after the discount of twenty percent, or simply a play Qizhe calculation.

Ambient temperature, according to regulations refers to the average maximum temperature of the hottest summer months. In fact, temperature changes, under normal circumstances, it affects the cable carrier is not great. Therefore, only certain temperature workshop or the area of ??hotter than 25 ℃ more before considering discounted.

Download different conditions such as heart insulated wire of aluminum wire in the flow calculation:

When the cross section of 10 mm2 wire wear tube, wire ampacity for 10 × 5 × 0.8 ═ 40 security; for high temperature, the wires are set out the flow rate of 10 × 5 × 0.9 ═ 45 security; if wearing a tube but also high temperatures, The carrying capacity of the wire 10 × 5 × 0.7 ═ 35 Ann.

(3) for the bare aluminum wire carrying capacity, the formulas that "the bare and half calculation plus half. This refers to the same cross-section bare aluminum or aluminum conductor insulated wire, cable ampacity can increase the half.

Such as bare aluminum wire ampacity calculations:

When the cross section of 16 mm2, the carrying capacity for the 16 × 4 × 1.5 ═ 96 security at high temperatures, the carrying capacity of 16 × 4 × 1.5 × 0.9 = 86.4 Ann.

(4) For the carrying capacity of copper wire, the formulas that "copper upgrade to count", to be copper wire cross-section of the order level, and then the aluminum condition evaluates.

Example, the section of 35 mm2 bare copper wire ambient temperature is 25 ℃, the carrying capacity is calculated as: ie 50 × 3 × 1.5 = 225 An upgrade to 50 mm2 bare aluminum wire.

For cable, the formulas in the introduction. Generally directly buried high voltage cable, in general, can be directly related to multiples of the first sentence of the formulas in the calculation. Such as 35 mm2 high-pressure armored aluminum cable burying the carrying capacity of 35 × 3 = 105 security. 95 mm2 wire and cable is approximately 95 × 2.5 ≈ 238 Ann.

Zero-line cross-section of the three-phase four-wire wire and cable, usually chosen as 1/2 of the phase line section. Of course, not be less than the minimum allowed cross-section required by the mechanical strength. In the single-phase line, the load current through the zero line and the line is the same as the zero line cross section with the phase line section.

www.tianlan88.com, ------- www. kuanglan88.com