Sproat Lake, Vancouver Island, BC

Mark and Sally’s RV Light Connections

Mark and Sally’s RV Light Connections

Part 1 (Conductor Sizes)

Mark and his wife Sally own an RV and want to add a couple of new devices to their 12-volt house battery bank. Although their RV is equipped with a shore power converter, they want these new devices to be powered directly from the battery bank, ensuring they remain functional even when the RV is not connected to shore power. They recently purchased a 10-watt LED puck light, perfect for reading or finding things at night at the back of the RV. Additionally, they bought a 100-watt LED bar for the front of the RV, providing extra visibility on the dark, unlit backroads they frequently travel.


Wiring Two Light Bulbs in an RV: Determining Conductor Sizes

To properly connect these two devices, it’s essential to understand the amount of current that will flow through the wires connecting them to the battery. Although adding the correct fuses and switches is also important, today’s lesson focuses solely on determining the appropriate cable sizes. We need this information to ensure we purchase the correct wire sizes when we go to the store.

In this lesson, we’ll calculate the appropriate wire conductor sizes for adding two new lights to a 12-volt DC house battery bank in an RV. Our focus will be on ensuring safe and efficient connections, without discussing the battery bank’s capacity at this point. Each circuit will have a total length of around 20 feet. This length is sufficient to run from the battery compartment in the underside of the RV to the first location at the back for the 10-watt LED light, and also 20 feet to the front where the 100-watt LED bar is situated.

Our two loads are:

  1. A 10-watt LED puck light.

  2. A 100-watt LED light bar (which could represent any 12-volt device, such as a TV).

Let’s go through the calculations to determine the correct wire sizes for each load.


Now that we know how much current will flow through Let’s add a 3% voltage drop. Voltage drop refers to the reduction in voltage as electrical current travels through a circuit. This phenomenon occurs because wires and other components have inherent resistance, which causes them to consume a small amount of the electrical energy they are transmitting.


When calculating voltage drop in a DC circuit, it is essential to account for the total length of the wire in the circuit, which includes both the outgoing and returning wires. This is because electrical current must travel from the power source to the load and back again to complete the circuit. Therefore, the total path the current travels is twice the distance from the power source to the load. This is referred to as a “round trip.”






AWG Sizing Chart

Although we calculated our available current per foot, you can easily download an AWG chart online. By knowing the current draw (ampacity) of your device, these types of charts provide the distance in feet per gauge of conductor and its ampacity. This can simplify the process of selecting the appropriate wire gauge for your specific needs.

The main calculation you need to do involves determining the ampacity using Ohm’s Law once you know the wattage of a device and your source voltage. With this information, you can consult a chart to figure out the appropriate conductor size and length for that particular size.


In conclusion, we’ve explored how to safely wire two new devices—a 10-watt LED puck light and a 100-watt LED Bar light—into Mark and Sally’s RV using their 12-volt DC house battery bank. By calculating the appropriate wire conductor sizes using Ohm’s law, we ensure efficient connections without exceeding safe current capacities or causing excessive voltage drops.

The same principles apply regardless of the device’s wattage—whether it’s a 25-watt device or a 200-watt device, the calculations remain consistent. Practicing with different scenarios allows you to understand the varying cable sizes required for different loads.

At IOTG Solar, we are committed to empowering others through education, helping them understand the fundamentals of building and maintaining reliable electrical systems. This knowledge ensures that devices like lights, TVs, or other 12-volt appliances operate reliably and safely, enhancing the functionality and convenience of RV living and beyond.


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