Understanding 12 volt automotive Cable - Comparing AWG B&S mm2

Calculating and installing the correct gauge cable in a 12 volt set up is paramount to any successful system.

Home of 12 Volt stock a huge range of 12 volt automotive cables in all sizes. But how do we compare AWG to B&S or mm2. It can be beyond confusing for even the most educated 12 volt enthusiast.

Can you use 240v cable with 12v system? 

One of the most important things to note is the difference between 240 volt cable and 12 volt cable. The differing voltages result in a very different construction of the cable. It is therefore crucial to note that these cables are not interchangeable on a system.

240 Volt power uses a higher voltage and therefore the power is easily transferred through cable with lesser, thicker copper strands. As the voltage starts at 210 - 250 volts, the voltage drop in this type of cable is significantly less over longer distances as the voltage starts higher. Many appliances that run on mains power will operate between 220 - 250 Volts. If the initial voltage of cable run starts at 240 volts and is extended over a significant distance (say 30mt), then even a voltage drop down to 220 volts will not be significant enough to cause an appliance to stop working or reduce in performance. 

Compare this above example with a 12 volt cable, this type of cable is built with many smaller strands of copper, designed to easily transfer the lower voltage with the aim to reduce voltage drop. Many smaller strands of copper work better to transfer the lower voltage with the less level of resistance.

In a 12 volt system, the starting voltage is low (between 10.5 volt ~ 14.5 Volts), this means that even the smallest increment of voltage drop can result in a large difference of power harnessed / lost.

Consider this: A charged battery in a 12 volt system is 12.7 Volts (12.7V = 100%), however, the same battery is 50% charged when the voltage reaches 12.2 Volts.

This 0.5 volt change is the difference in half of your battery capacity. This can show you just how significant a voltage drop can really be in a 12 volt system.

(12.7 volts = 100% | 12.5 Volt = 80% | 12.2 Volts = 50% | 10.5 Volts = Flat) 

It is now easy to understand why it is so important that we use a 12 volt cable in 12 volt installation and why it is important to use a heavier gauge cable (a greater number of strands) in any system that is running over extended lengths. This will aid in minimizing voltage drop.

Now we have identified the difference in 240 volt cable vs 12 volt cable, let's break down the difference in the styles of ratings (automotive / AWG / B&S)

How to compare mm2 B&S and AWG ratings? 

At Home of 12 Volt online we rate all of our cable as 12 volt automotive. This rating will provide a mm2 sizing, along with an amperage rating based over approx. 5mt in 30*degree ambient temperature.

Throughout the world, there are several different methods of measuring cable, however, there is a way 

What if you use a twin core cable instead of single core? Does this make a difference in performance? 

The simple answer is Yes. It does. 

Cable is often measured over a 5mt distance in approx. 30*C temperature. 

When running a single core of cable, for example, a single 5mt length of 8mm cable, then the efficiency factor is equal to 1. This means if the cable is rated to 74 Amps, then you will receive a full 74 Amps from the cable over this distance in this heat. 

Compare this to running a length of 5mt Twin core (2 x cores of cable sheathed together), then the efficiency factory is now equal to 0.8. This means we immediately lose 20% efficiency when running a twin core cable, compared to that of a single core. 

The same 8mm cable that was rated at 74 Amps in a single core, is now reduced to a 59Amp rating when run as a twin core. 

It is important to consider several factors when running cable for your 12 volt installation, factors such as: 

• How long is total length of cable used?
• What is the overall power draw used for the cable run? 
• How much do the appliance(s) on this cable run draw at maximum load? 
• What levels of heat will the cable be exposed to? 
• How will you be fusing the length of cable to the battery?

These are only a small number of the questions you may ask yourself when running cable for a 12 volt installation. Taking the time to answer these questions can make an incredible difference to the performance of an overall system. 

Cutting corners on quality 12 volt cable is not recommended. Consider this: if the pipes in a water system are weak and small, then you will never transfer the water required and you may end up with no pressure at the end of the line.. this is the same with your cable in your 12 volt system. 

If you are in doubt of what cable to use for your system, then why not contact us directly on 08 8391 3121.

Home of 12 Volt Online use only Australian manufactured oxygen free cable; High quality and reliable.

Did you know Home of 12 Volt online manufacture custom leads? 

If you are in need of assistance for making leads to suit a particular application, then why not contact our team direct on 08 8391 3121. For only a small fee per lead, our staff can help make up everything you need, to save you money on tools that you may only use once!