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Wire and cable ampacity analysis
Cable ampacity mouth decision:
Estimation formulas:
Two five multiplied by nine the next, minus a cis numbers go up.
Thirty three five five times, both in groups minus point five.
Plus there is a change premise translated into high-temperature copper grade% off.
Wear tube root number two three four, eighty-seven tickets full stream.
(1) This section formulas for various insulated wire (rubber and plastic insulated wire) carrying capacity (safe current) is not explicitly stated, but "cross section multiplied by a certain factor" to that obtained through mental arithmetic.
As can be seen from Table 5 3: Multiple cross-section decreases with.
"Two five multiplied by nine the next, minus a cis numbers go up," said the 2.5mm 'and below the various sectional aluminum insulated wire, cross-section of its carrying capacity is about 9 times the number. If 2.5mm 'conductors carrying capacity of 2.5 × 9 = 22.5 (A).
From 4mm 'and above the wire carrying capacity and the number of multiple relations section along line number is up row, multiple successive reduction l, ie 4 × 8,6 × 7,10 × 6,16 × 5, 25 × 4.
"Thirty-three five five times, both in groups minus point five," said the 35mm "carrying capacity of the wire is 3.5 times the number of sections, ie 35 × 3.5 = 122.5 (A). From 50mm 'and above the wire, which contains flow and multiple relationship between the number of sections into two by two into a group of line numbers, multiple order minus 0.5. is 50,70 mm' carrying capacity of the wire cross-section number 3
X; 95,120 mm "wire ampacity the number of cross-sectional area is 2.5 times, and so on.
"Canada has changed the premise translated into high-temperature copper grade% off." The formulas are aluminum insulated wire, Ming deposited at ambient temperature 25 ℃ under the premise and set. If aluminum insulated wire for surface at an ambient temperature higher than 25 ℃ long-term areas of wire ampacity accordance with the above formulas calculation approach, then you can call Jiuzhe; when not using aluminum instead insulated copper wire, Its carrying capacity is somewhat larger than the same size aluminum, according to the above method of calculation formulas than aluminum to increase the carrying capacity of a line number.
Such as 16mm 'carrying capacity of copper wire, aluminum wire can be calculated 25mm2.
Select cable cable ampacity calculations (based on the current selection cable):
Conductor ampacity and conductor cross section, but also with the wire material, type, method of laying and ambient temperature and so on, many factors influence the calculations are more complicated. Various conductor ampacity is usually available from the manual search.
But the use of formulas together with some simple mental arithmetic, can be calculated directly, without look-up table.
1 formulas aluminum insulated wire ampacity multiple relationship with the cross-section
10 under five, 100 on two,
25,35, four, three realms.
70,95, two and a half.
Wear tube, temperature, eight at 10%.

Bare plus half.
Copper into the class count.
Help formulas for various sections of the carrying capacity (Ann) is not explicitly stated, but with a certain cross section multiplied expressed in multiples.
This will be our common conductor nominal cross section (square millimeters) are arranged as follows:
1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185 ......
(A) The first sentence formulas indicate aluminum insulated wire ampacity (Ann), according to the cross section calculated in multiples. Formulas in Arabic numerals wire cross section (square millimeters), Chinese numerals multiples.
The cross section formulas lined up with multiple relationships are as follows:
1 16,25 35,50 70,95 10 120 or more
﹀ ﹀ ﹀ ﹀ ﹀
Two and a half twice three times four times five times
Now and then, and formulas were even more clear, formulas "10 under five" refers to section 10 below carrying capacity is five times the cross-section values. "100 on the two" (read one hundred on two) refers to section 100 of the carrying capacity of more than twice the value of the cross-section. 35 is a cross-section 25 and the boundary between the quadruple and triple. This is the formulas "25,35, four realms." The sections 70,95 was 2.5 times.
As can be seen from the above arrangement: In addition to 10 or less and more than 100, the middle of the wire cross-section of every two specifications are the same kind of multiples.
Such as aluminum insulated wire, the ambient temperature is less than 25 ℃ when the load flow calculation:
When the cross-section of 6 mm2 when considered carrying capacity of 30 A;
When the cross-section of 150 mm2 when considered safe carrying capacity of 300;
When the cross-section of 70 mm2, the carrying capacity of 175 considered safe;
From the above arrangement can also be seen: a multiple decreases with the cross-section, the junction of the multiple shift, the error is slightly larger. Like sections 25 and 35 are four times and three times the boundary, 25 genera and four times the range, it is counted as 100 A by formulas, but according to the manual for the 97 safety; while 35 On the contrary, according to formulas counted as 105 security, but look-up table 117 Ann. However this did not affect the use. Of course, if "a few chest", the choice of conductor cross section, do not let it fill 25 to 100 Ann, 35, may be slightly more than 105 An even more correct. Similarly, 2.5 mm2 conductor position in the beginning of five times, it is more than five times the actual (maximum up to 20 amps or more), no more than the wire in order to reduce power consumption, usually do not need to use such a large current, manual generally
Standard 12 Ann.
(2) is on the premise behind the three formulas change process. "Wear tube, temperature, eight 10%" means: If through pipe laying (including laying groove boards, etc., that lead plus a protective cover layer, unknown exposed), calculation, call discount for each purchase; if the ambient temperature exceeds
25 ℃, and then calculate a discount, if only through pipe laying, the temperature is over 25 ℃, the discount of twenty percent after a discount, or simple press play percentage calculation.
On the ambient temperature, according to delimit the hottest summer months is the maximum temperature uniformity. In fact, the temperature change, in general, it does not affect the current-carrying conductors greatly.
Therefore, the workshop or only for certain temperature hotter regions, more than 25 ℃ higher, before considering discounted.
Such as aluminum center insulated wire in a different premise download flow calculation:
When the cross-section of 10 mm2 wear tube, then the carrying capacity of 10 × 5 × 0.8 ═ 40 Ann; case of high temperature, then the carrying capacity of 10 × 5 × 0.9 ═ 45 Ann; if wearing a tube and high temperature, then the carrying capacity of
10 × 5 × 0.7 ═ 35 Ann.

(3) For the bare aluminum carrying capacity, formulas that "bare plus half" that is calculated plus half.
This refers to the same section of bare aluminum and aluminum insulated wire compared to the carrying capacity can be increased by half.
Such as bare aluminum ampacity calculations:
When the cross-section of 16 mm2, then the carrying capacity of 16 × 4 × 1.5 ═ 96 Ann, if the high temperature, the carrying capacity of 16 × 4 × 1.5 × 0.9 = 86.4 Ann.
(4) For the carrying capacity of copper wire, formulas that "copper wire into the class count," the upcoming cross-section copper wire promoted an order, and then calculate the corresponding aluminum premise.
Such as cross-section of 35 mm2 bare copper wire ambient temperature is 25 ℃, carrying capacity is calculated as: Press into the class of 50 mm2 bare aluminum that was 50 × 3 × 1.5 = 225 Ann.
For cable, formulas are not the first volume. Generally directly buried high-voltage cables, in general, can be directly used in the first sentence of the relevant formulas multiples. Like 35 mm2 High armored aluminum cables laid underground ampacity of 35 × 3 = 105 Ann.
95 mm2 to about 95 × 2.5 ≈ 238 Ann.
Three-phase four-wire system in the zero line cross-section, usually chosen phase line section of about 1/2. Of course, according to the mechanical strength of not less than the minimum required by section promised. In the single-phase line, because the zero line and the phase line adopted by the load current is the same, so the zero line section should be the same phase line section.

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