CABLE GUIDE
***Before you say it, yes, we know our recommended maximum amperages are considered conservative when compared to other recommendations you've no doubt read online. The assumptions we use for our recommendations are on the safer end, but also aren't unrealistic. It is important you understand your loads, lengths and ambient temperatures to best pick the cable suited to your circumstances***.
However, at the end of the day, it is your money, equipment and safety on the line so the end decision lies with you!***
Choosing the right cable for your systems needs can be a daunting task given the over complicated information online and what appears to be some pretty in depth calculations required to make sure you're not setting everything on fire. Before we get started, there are a few things you'll need to know to help understand how we come up with our recommendations.
Voltage Drop:
Voltage drop refers to the decrease in electrical voltage as current flows through a cable due to the resistance of that cable.
Here's why voltage drop is important to consider:
Performance and Efficiency:
- Voltage drop can affect the performance of your electrical devices. If the voltage drops too much, devices may not operate as intended, and their efficiency can be compromised
Heat Generation:
- As current flows through a wire, resistance causes the wire to heat up. Excessive voltage drop can lead to more heat generation, and in some cases, this could be a safety concern.
- The voltage supplied at the source may not be the same as the voltage received by the device (load). If the wire is too long or not adequately sized, the voltage reaching the load could be significantly lower than the source voltage.
- In 12V lighting systems, voltage drop can result in reduced brightness of bulbs or LEDs.
- In 12V systems powered by batteries, excessive voltage drop can lead to faster battery drain.
A voltage drop of 3% (or 0.36v) is considered the "safe" standard less critical uses which typically draw a low current and require smaller gauge wire. A voltage drop of 2% (or 0.24v) is used for more critical applications such as main feed wiring and inverters.
The recommendations made for our Anderson Cables assume a voltage drop of 3%.
Derating Factor
The derating factor of cables due to heat refers to the reduction in the maximum current-carrying capacity of a cable when it operates at higher temperatures. Cables, when subjected to elevated temperatures, may not be able to handle as much current as they would at lower temperatures.
Here's why the derating factor due to heat is important to consider:
Cable Temperature Limit:
- Cables have temperature ratings indicating the maximum temperature they can withstand without compromising their insulation or other properties. Operating cables at temperatures exceeding this limit can lead to deterioration and potential failure. These derating factors are as follow:
|
Derating Factors for Ambient Temperatures °C
|
|||||
| Temp | 30c | 40c | 50c | 60c | 70c |
|
Factor |
1 | 0.9 | 0.76 | 0.6 | 0.45 |
Increased Resistance:
- As the temperature of a cable rises, its electrical resistance typically increases. This increase in resistance results in more heat generation, creating a feedback loop that can further raise temperatures.
Conductor Overheating:
- When cables carry current, they naturally heat up due to the resistance of the conductors. If the ambient temperature is already high, or if the cables are bundled together, this additional heat can lead to overheating.
Fire Hazard:
- Excessive heat can pose a fire hazard. Derating factors are applied to prevent cables from reaching temperatures that could potentially ignite nearby materials or damage the insulation.
For the purpose of our standard Anderson Cables, we use an ambient temperature of 50c which gives a derating factor of 0.76. We have chosen 50c as it's not uncommon for ambient temperatures of even shaded systems to reach this.
Well that's all still very complicated, can you put this into something useable for me please?
Of course we can! Below is a chart of the different wire gauges and the maximum amperage we recommended putting through each cable based on it's length:
| Maximum Recommended Amperage | ||||
| Length (m) | 6AWG (13.5mm2) | 8AWG (7.71mm2) | 11AWG (4.59mm2) | 13AWG (2.90mm2) |
| 0.5 | 82* | 59* | 38* | 29* |
| 1 | 82* | 59* | 38* | 27 |
| 2 | 64 | 37 | 22 | 13 |
| 3 | 43 | 24 | 14 | 9 |
| 4 | 32 | 18 | 11 | 6 |
| 5 | 25 | 14 | 8 | 5 |
| 6 | 21 | 12 | 7 | 4 |
| 7 | 18 | 10 | 6 | 3 |
| 8 | 16 | 9 | 5 | 3 |
| 9 | 14 | 8 | 4 | 3 |
| 10 | 12 | 7 | 4 | 2 |
| 11 | 11 | - | - | - |
| 12 | 10 | - | - | - |
| 13 | 9 | - | - | - |
| 14 | 9 | - | - | - |
| 15 | 8 | - | - | - |
*Limited by manufacturers cable amp rating
^Assumes maximum 3% voltage drop with an ambient temperature of 50c
The obvious yet much needed disclaimer
As you have probably gathered, there are so many factors at play that influence which cable you need for your system which makes the question "Which cable do I buy?" a hard question to answer. The recommendations made above are made using very specific assumptions and are to be used as a guide only. You will need to tweak these recommendations based on your individual system and it's environment and uses. If in doubt, upsize! The only real downside to upsizing is cost and the cost of going too small will far exceed the cost of upsizing your cable.
I've had a look at your recommendations and they seem ridiculous. The biggest seller of 12v equipment in the country (that may or may not rhyme with the word Stings) are selling a 6m 14 AWG Anderson Cable that is rated to 20 amps, yet you're telling me your 6m 6 AWG cable is only rated to 21 amps?!
Correct! "Stings" list no assumptions in their ratings so numbers can easily be manipulated. If we assume the ambient temperature the cable being used is 30c or less and the connected devices are suitable to handle a 16% voltage drop, then yes, you can use a 6m 14 AWG Anderson Cable safely in this scenario.
Extra Resources:
- Enerdrive Cable Sizing Selection Chart: This chart, found here, expands on the above and includes wire recommendations right up to 0000AWG!
- Topwire Traveller Cable Size Calculator: This calculator, founder here, allows you to punch in your conditions and spits out the minimum recommend wire for the job.
- Facebook Groups: Facebook has a plethora of groups dedicated to DIY systems. The best two I've come across is "The DIY 12/24v camping 4wd set-ups" group found here and the "Everything 12/24v camping & 4wd DIY offgrid setups" group found here. As with all Facebook groups, use at your own risk! While there's a of great information in this group, it's still riddled with keyboard warriors and armchair experts.
As always, if in doubt, flick us an email at sales@nbcampingequipment.com.au with your queries and we'll help where we can.