What Size Armoured Cable For Outdoor Lighting

Choosing the correct size of armoured cable for outdoor lighting is crucial for ensuring safe and reliable operation. The cable needs to handle the electrical current required by the lighting fixtures while also protecting the wiring from the elements. Factors such as the distance of the run, the number of fixtures, and the type of lighting all play a role in determining the appropriate cable size.

Armoured cable, also known as 'BX cable' or 'cable with metal sheath', is a type of electrical cable commonly used in outdoor applications due to its robust construction. It consists of insulated conductors encased in a protective metallic sheath, often made of steel or aluminum. The armouring provides protection against mechanical damage, moisture, and rodents, making it suitable for outdoor installations.

Understanding Current Draw and Amperage

The first step in determining the correct cable size is to calculate the total current draw of the lighting fixtures. This information is typically found on the fixture's specifications or on the packaging. The current draw is measured in amps (A), and it represents the amount of electrical current that the fixture needs to operate.

To determine the total current draw, add the amperage of each individual fixture in the circuit. For example, if you have five 100-watt LED light bulbs, each drawing 0.1 amps, the total current draw would be 0.5 amps (5 x 0.1 amps).

Cable Size and Ampacity

Once you have calculated the total current draw, you need to select a cable with an ampacity that meets or exceeds this value. Ampacity refers to the amount of current a cable can safely carry without overheating. The ampacity of a cable is influenced by its size, the type of insulation, and the ambient temperature.

Cable sizes are typically designated by their American Wire Gauge (AWG) number. A lower AWG number indicates a larger diameter cable, capable of carrying more current. For outdoor lighting circuits, common cable sizes range from 12 AWG to 10 AWG. Consult a cable ampacity chart or electrical code specifications to find the ampacity ratings for different cable sizes and materials.

Distance and Voltage Drop

The distance of the cable run also plays a crucial role in determining the appropriate cable size. As the distance increases, the voltage drop along the cable becomes more significant. Voltage drop occurs when there is a reduction in voltage along the cable due to resistance. Excessive voltage drop can cause the lighting fixtures to operate at reduced brightness or even fail.

To minimize voltage drop, it is essential to choose a cable with a sufficiently large cross-sectional area. Larger cables have lower resistance and therefore less voltage drop. If the distance of the run is long, a larger cable size might be necessary to mitigate the voltage drop. Refer to voltage drop calculators or consult with an electrician to determine the appropriate cable size for the specific distance involved.

Safety Considerations

In addition to the considerations mentioned above, several safety factors need to be taken into account when choosing armoured cable for outdoor lighting. The cable chosen should be suitable for the environmental conditions where it will be installed. This includes factors such as temperature extremes, moisture, and potential exposure to sunlight.

Ensure that the cable meets the electrical code requirements for outdoor installations. Furthermore, it is crucial to use appropriate connectors and termination methods to ensure a watertight seal and prevent electrical hazards.