# Calculation of the cross-section of DC electrical cables

### Manual

### Intensity:

### 2. Example:

### The formula to use for copper conductors is:

S = 0.017 x L x I / PT

S = section of the copper conductor expressed in square millimeters

L = outbound + return length of the conductor expressed in meters

I = intensity expressed in Amperes

PT = loss of tension accepted at the level of the cables expressed in

Volts

Manual

Length calculation:

Whatever the nature of the shell, it always requires a "go" or positive conductor in

generally red in color and a "return" or negative conductor in black color.

As specified in Division 240, hull material should never be used as

as a driver.

### Intensity:

The nominal intensity is sometimes provided: in this case, nothing could be simpler.

Often, only the power of the device is indicated. In this case, we have to calculate

intensity using the following formula:

P = U x I i.e. I = P / U

P = Power expressed in Watts

U = nominal voltage of the installation (12 V, 24 V or 48 V) expressed in Volts

I = Intensity expressed in Ampere

PT or loss of voltage in the cables:

A current passing through the cables generates a voltage (Ohm's law).

Division 240 specifies that this must remain less than 5% of the rated voltage of

installation either:

Maximum allowed PT in 12 V = 0.6 V (5% of 12 V)

24V = 1.2V (5% of 24V)

Reasonable PT a priori in 12 V = 0.3 V (2.5% of 12 V)

24V=0.6V (2.5% of 12V)

2. Example:

Installation of a 110 W 12 V pump

Distance between the fuse or circuit breaker and the pump via the complete route: 7

meters. Go + return = 14 m.

The nominal current is: 110 / 12 = 9.2 A

The strictly minimum section of the conductor must be:

0.017 x 14 x 9.2 / 0.6 = 3.6 mm²

The so-called “reasonable” section is:

0.017 x 10 x 9.2/0.3 = 7.3 mm²

A section of 4² is sufficient "legally" but a conductor of 6 is preferable.

As far as I am concerned, I prefer to send the maximum voltage to the pumps and I

will carry out the installation in 10²

### Manual

### Intensity:

### 2. Example:

### The formula to use for copper conductors is:

S = 0.017 x L x I / PT

S = section of the copper conductor expressed in square millimeters

L = outbound + return length of the conductor expressed in meters

I = intensity expressed in Amperes

PT = loss of tension accepted at the level of the cables expressed in

Volts

Manual

Length calculation:

Whatever the nature of the shell, it always requires a "go" or positive conductor in

generally red in color and a "return" or negative conductor in black color.

As specified in Division 240, hull material should never be used as

as a driver.

### Intensity:

The nominal intensity is sometimes provided: in this case, nothing could be simpler.

Often, only the power of the device is indicated. In this case, we have to calculate

intensity using the following formula:

P = U x I i.e. I = P / U

P = Power expressed in Watts

U = nominal voltage of the installation (12 V, 24 V or 48 V) expressed in Volts

I = Intensity expressed in Ampere

PT or loss of voltage in the cables:

A current passing through the cables generates a voltage (Ohm's law).

Division 240 specifies that this must remain less than 5% of the rated voltage of

installation either:

Maximum allowed PT in 12 V = 0.6 V (5% of 12 V)

24V = 1.2V (5% of 24V)

Reasonable PT a priori in 12 V = 0.3 V (2.5% of 12 V)

24V=0.6V (2.5% of 12V)

2. Example:

Installation of a 110 W 12 V pump

Distance between the fuse or circuit breaker and the pump via the complete route: 7

meters. Go + return = 14 m.

The nominal current is: 110 / 12 = 9.2 A

The strictly minimum section of the conductor must be:

0.017 x 14 x 9.2 / 0.6 = 3.6 mm²

The so-called “reasonable” section is:

0.017 x 10 x 9.2/0.3 = 7.3 mm²

A section of 4² is sufficient "legally" but a conductor of 6 is preferable.

As far as I am concerned, I prefer to send the maximum voltage to the pumps and I

will carry out the installation in 10²

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