By :Mahendra Bandal

Technocrats Plasma Systems Private Limited Mumbai

Welding cables- the current carrier between machine and the job.

Welding cable size selection- an important but commonly unknown knowledge; often ignored by users as well as manufacturers.

Insufficient cable size- the cause of unsatisfactory performance many a times which goes unnoticed; ultimately service dept. and goodwill of the company suffers.

Q. Standard length of cables used for commercial welding e.g. Maintenance workers, fabricators etc. ?

3-5 meters.Q. What conductor material should ideally be

used?CopperQ. Range of cable length in heavy industrial

applications e.g. Tube mill, ship yards etc. ?15-50 meters.

Welding cables are affected by various factors which cause power losses during welding.

Power dissipation factors:1.Length of cable.2.Cross- sectional Area of cable.3.Resistance of the material.4.Ambient temperature.

Consider Solaris 400:o/p current(I)= 300 ampsArc voltage(V)= 32 volts

Arc voltage = 20+(0.04*I)o/p power(P) = V x I= 9.6kW

This is the o/p power when welding with short cables up to distances of 5 meters.

Now, What about o/p power when welding cables

used are of lengths ranging up to 50 meters?

Power dissipation along cable length.Dissipated power = I2 x RResistance(R) = ρL / A

ρ= 1.68 x10-8 Ωm for copper and 2.65 x10-8 Ωm for aluminum.

Suppose the length of welding cable is 30 meters.R= ρL / A (A= 95 mm2)

= 1.68 x10-8 Ωm x30m / 95x10-6 m2. =5.3052 mΩ.

R= ρL / A (A= 35 mm2) = 1.68 x10-8 Ωm x30m / 35x10-6 m2. =14.4 mΩ

Dissipated power along cable of area 95 mm2 = I2 x R= 3002 x 5.3052m= 477.468 W

Dissipated power along cable of area 35 mm2 = I2 x R= 3002 x 14.4m= 1.296 kW

Total Power At Job End = O/P at terminal – Power dissipated along the cable.

When cable area -95 mm2 = 9.6 kW – 477.468 W = 9.1 kW

When cable area -35 mm2 = 9.6 kW – 1.296 kW = 8.304 kW

*All calculations are considering copper cables & an ambient temperature of 20˚C.

Hence, to reduce power losses, the diameter/cross sectional area of cable should increase as cable length increases.

o/p power=9.6 kW

Length= 30 mts.Area= 35 mm2

Work Piece

Electrode holder

rod

Power= 8.304 kW

COMMON INDUSTRIAL PRACTICEThe case study was considering both +ve & -

ve cables to be of 30 mtr. Length.Now, as per common industrial practice, the

job cable is replaced by common strips, kept one on top of the other.

This leads to a huge voltage drop at the contact point as the contact area is very small, leading to sparks during welding.

This drop causes further power losses.

o/p power=9.6 kW

Length= 30 mts.Area= 35 mm2

Work Piece

Electrode holder

rod

Power << 8.304 kW

Job clamp

Common strips

Meters

Ampere

15 25 30 40 45 55 60

200 35mm2

50mm2

70mm2

95mm2

95mm2

120mm2

120mm2

250 50mm2

50mm2

95mm2

120mm2

120mm2

300 50mm2

70mm2

95mm2

120mm2

350 50mm2

95mm2

120mm2

400 70mm2

120mm2

SUGGESTED AMPACITY FOR WELDING CABLE DISTANCE IN METERS

The first preference of any user when purchasing an inverter machine is the low power consumption of this technology.

The excess power losses in the cables(around 1 kW) increase the machine’s power losses, making the low power consumption plus point ineffective.

Advice our valued customers to save power by making the right choice.