7/29 wire is seven copper strands, each 0.029 inch (0.737 mm) thick, which makes 2.98 mm² of copper. Shops sell it against the 2.5 mm² metric size. In conduit on a single-phase circuit it carries about 26.6 A at 30°C and 23.1 A at 40°C, so in a Pakistani summer it suits a 20 A breaker. 3/29 has only 1.28 mm² of copper, less than the 1.5 mm² it is sold against.
The calculator works out the current your load draws, picks the breaker, applies heat and grouping factors, then checks voltage drop over your cable length. It gives the smallest metric size and the smallest Pakistani strand size that pass both checks, with every step shown.
Cable size chart: Pakistani wire sizes in mm and amps
Copper wires with PVC insulation, as sold in 90 m coils. Amps are the BS 7671 table ratings at 30°C air. The last column applies the 40°C factor (0.87) and gives the largest standard breaker the wire can sit behind.
| Wire | Strand | Copper (mm²) | Sold as | Conduit, 1 phase (A) | Conduit, 3 phase (A) | Clipped, 1 phase (A) | Drop 1 phase (mV/A/m) | Largest MCB, conduit 1 phase at 40°C |
|---|---|---|---|---|---|---|---|---|
| 3/.029 | 0.737 mm | 1.28 | 1.5 mm² | 15.7 | 13.9 | 18 | 35.6 | 13 A |
| 7/.029 | 0.737 mm | 2.98 | 2.5 mm² | 26.6 | 23.3 | 30.2 | 15.7 | 20 A |
| 7/.036 | 0.914 mm | 4.60 | 4 mm² | 34.7 | 30.4 | 40 | 9.9 | 25 A |
| 7/.044 | 1.118 mm | 6.87 | 6 mm² | 44.5 | 39 | 50.9 | 6.7 | 32 A |
| 7/.052 | 1.321 mm | 9.59 | 10 mm² | 55.4 | 48.6 | 63.2 | 4.7 | 40 A |
| 7/.064 | 1.626 mm | 14.53 | 16 mm² | 71.3 | 63.6 | 81.6 | 3.2 | 50 A |
| 19/.052 | 1.321 mm | 26.03 | 25 mm² | 103.5 | 91.2 | 116.8 | 1.7 | 80 A |
| 19/.064 | 1.626 mm | 39.43 | 35 mm² | 132.7 | 117.1 | 153.1 | 1.2 | 100 A |
| 19/.083 | 2.108 mm | 66.32 | 70 mm² | 184.5 | 164.2 | 224.4 | 0.8 | 125 A |
Imperial wires are rated from their real copper area, in a straight line between the two nearest metric sizes in the BS 7671 table. That never gives a wire more than the table would. Drop is the voltage lost per amp per metre of run on a single-phase circuit.
What 3/29, 7/29 and 7/44 mean
Pakistani house wire is named by the number of strands and the thickness of each strand in inches. 7/.029 (said as seven by twenty-nine) is 7 strands of 0.029 inch. The copper area is the number of strands times the area of one strand:
- Strand diameter: 0.029 x 25.4 = 0.737 mm.
- Area of one strand: 3.1416 ÷ 4 x 0.737 x 0.737 = 0.426 mm².
- Seven strands: 7 x 0.426 = 2.98 mm².
The same sum gives 1.28 mm² for 3/29, 4.60 mm² for 7/36, 6.87 mm² for 7/44, 9.59 mm² for 7/52 and 14.53 mm² for 7/64. Makers label these as 1.5, 4, 6, 10 and 16 mm². Most are close, but 3/29 and 7/64 carry noticeably less copper than their labels, which is why the calculator rates them by their own area.
Which wire goes where in a house
In most Pakistani homes, lights and fans run on 3/29, socket circuits on 7/29, a 1.5 ton AC or water motor on 7/36, and a 2 ton AC or instant geyser on 7/44. The supply from the meter to the main board is usually 7/52 or 7/64. These are habits, not rules: the size you need depends on the breaker, the heat and the length of the run.
Electrical cable size chart in amps (mm²)
Single-core copper PVC cables, BS 7671 Table 4D1A and 4D1B. Conduit means reference method B, clipped means reference method C. Single phase is 2 loaded cables, three phase is 3 or 4.
| Size | Conduit, 1 phase (A) | Conduit, 3 phase (A) | Clipped, 1 phase (A) | Clipped, 3 phase (A) | Drop 1 phase (mV/A/m) | Drop 3 phase (mV/A/m) | Largest MCB, conduit 1 phase at 40°C |
|---|---|---|---|---|---|---|---|
| 1 mm² | 13.5 | 12 | 15.5 | 14 | 44 | 38.1 | 10 A |
| 1.5 mm² | 17.5 | 15.5 | 20 | 18 | 29 | 25 | 13 A |
| 2.5 mm² | 24 | 21 | 27 | 25 | 18 | 15 | 20 A |
| 4 mm² | 32 | 28 | 37 | 33 | 11 | 9.5 | 25 A |
| 6 mm² | 41 | 36 | 47 | 43 | 7.3 | 6.4 | 32 A |
| 10 mm² | 57 | 50 | 65 | 59 | 4.4 | 3.8 | 40 A |
| 16 mm² | 76 | 68 | 87 | 79 | 2.8 | 2.4 | 63 A |
| 25 mm² | 101 | 89 | 114 | 104 | 1.8 | 1.56 | 80 A |
| 35 mm² | 125 | 110 | 141 | 129 | 1.3 | 1.13 | 100 A |
| 50 mm² | 151 | 134 | 182 | 167 | 1 | 0.87 | 125 A |
| 70 mm² | 192 | 171 | 234 | 214 | 0.72 | 0.63 | 125 A |
| 95 mm² | 232 | 207 | 284 | 261 | 0.56 | 0.49 | 125 A |
Ratings fall in heat: multiply by 0.94 at 35°C, 0.87 at 40°C, 0.79 at 45°C and 0.71 at 50°C. With 2 circuits in one conduit multiply by 0.80, with 3 by 0.70 and with 4 by 0.65.
How to calculate cable size
- Current. Single phase: watts ÷ (230 x power factor). Three phase: watts ÷ (1.732 x 400 x power factor). Use 1 for heaters and 0.8 for motors and AC units if you do not know it.
- Breaker. Take the next standard size at or above that current: 6, 10, 13, 16, 20, 25, 32, 40, 50, 63 A and so on.
- Derate. Divide the breaker rating by the temperature factor and the grouping factor. The answer is the table rating the cable needs.
- Size by current. Pick the smallest cable whose table rating is at least that figure.
- Voltage drop. Multiply the cable's mV/A/m by the current and the one-way length in metres, then divide by 1,000. Keep it within 3% for lighting (6.9 V on 230 V) and 5% for other circuits (11.5 V on 230 V, 20 V on 400 V).
- Take the bigger of the two sizes.
Worked examples
A 2,500 W circuit in conduit
Single phase, power factor 0.8, 25 m from the board, 40°C.
- Current: 2,500 ÷ (230 x 0.8) = 13.6 A, so a 16 A breaker.
- Table rating needed: 16 ÷ 0.87 = 18.4 A. 1.5 mm² is rated 17.5 A, too little; 2.5 mm² is rated 24 A.
- Drop on 2.5 mm²: 18 x 13.6 x 25 ÷ 1,000 = 6.1 V, or 2.7%.
Answer: 2.5 mm² or 7/29. 7/29 is rated about 26.6 A in the table and 23.1 A after the heat factor.
A 15 kW three-phase shop load
400 V, power factor 0.8, 40 m, clipped to the wall, 40°C.
- Current: 15,000 ÷ (1.732 x 400 x 0.8) = 27.1 A per phase, so a 32 A breaker.
- Table rating needed: 32 ÷ 0.87 = 36.8 A. 4 mm² is rated 33 A; 6 mm² is rated 43 A.
- Drop on 6 mm²: 6.4 x 27.1 x 40 ÷ 1,000 = 6.9 V, or 1.7% of 400 V.
Answer: 6 mm² or 7/44. 7/36 falls just short at about 36.0 A.
A long run where voltage drop decides
A 3,000 W heater, power factor 1, 60 m away, in conduit at 40°C. The current is 13.0 A and the breaker 16 A, so 2.5 mm² passes on current. But 5% of 230 V over 60 m allows only 14.7 mV/A/m, and 2.5 mm² drops 18. The answer moves up to 4 mm² or 7/36, which loses 8.6 V (3.7%) on 4 mm².
A licensed electrician must confirm the final wire and breaker before the circuit is switched on. These figures cover copper single-core PVC wires only. They do not cover earthing, loose joints, cheap undersized wire or a breaker that does not match the cable. For the load of a whole house, add up your appliances in the solar load calculator first.
Cable size questions
What is 7/29 wire size in mm?
7/29 is 7 strands of 0.029 inch, or 0.737 mm, copper. That is 2.98 mm² of copper, and it is sold as the 2.5 mm² equivalent. In conduit on a single-phase circuit it is rated about 26.6 A at 30°C, or 23.1 A in 40°C summer air, enough for a 20 A breaker.
What is 3/29 wire size in mm?
3/29 is 3 strands of 0.737 mm copper, which is 1.28 mm². Shops call it the 1.5 mm² size, but it has about 15% less copper. In conduit it is rated about 15.7 A at 30°C and 13.7 A at 40°C, so it suits a 10 A or 13 A breaker for lights and fans.
How do I choose a 3 phase cable size?
Divide the load in watts by 1.732 x 400 x power factor to get the current in each phase. Pick the next breaker size, divide it by the heat factor, and choose the cable from the three-phase column. Then check voltage drop against 5% of 400 V, which is 20 V. A 15 kW load at 0.8 power factor draws 27.1 A and needs 6 mm² or 7/44 at 40°C.
Which wire size for a 20 A or 32 A breaker?
Choose the wire by the breaker, not only by the appliance. In conduit at 40°C, a 20 A breaker needs a table rating of 23.0 A, so 2.5 mm² or 7/29. A 32 A breaker needs 36.8 A, so 6 mm² or 7/44 on a single-phase circuit. A long run may need one size larger for voltage drop.
Why does heat change the cable size?
Cable ratings are worked out for 30°C air. PVC insulation must stay at or below 70°C, so in hotter air the wire can take less current before it overheats. At 40°C a cable carries 87% of its table rating, and at 50°C only 71%. Wires bunched in one conduit also heat each other, so two circuits together carry 80%.
How do I calculate voltage drop in a cable?
Multiply the cable's mV/A/m figure by the current in amps and the one-way length in metres, then divide by 1,000 to get volts. For 2.5 mm² (18 mV/A/m) carrying 13.6 A over 25 m, that is 6.1 V, or 2.7% of 230 V. Keep lighting within 3% and other circuits within 5%.
Last reviewed 1 October 2026. Results are estimates; official notices always take precedence.