How To Choose Wire And Cable Gauge

Using the right wire or cable gauge is incredibly important. Unfortunately, the decision of which gauge to use is often made of a mixture of the cost of cable and the best guess of the decision maker. More often than not, this isn’t a big deal. Even if it means an accessory not working as well as it could, it may go unnoticed. In a worse case scenario, a gauge too small could cause a critical component to fail, or worse, a wire to overheat and possibly cause serious damage to the vehicle.

Below we’ll look at what we can keep in mind as general rules of thumb, and some decision-making guidelines as well as how to get the most out of your cable so prevent premature wear or damage.

How to choose the right gauge

Not many of us are likely to know how important wire or starter gauge really is. Many have heard it said that vehicle manufacturers reduce wire gauge to save on overall vehicle weight, and cost of material. If that is really the case it leads to the opinion that a larger gauge for any given application is a luxury. Some may also believe that the larger the gauge, the better. Always. Neither side is correct.

Choosing too large of a wire is essentially wasteful. The amount of energy it takes to pass current through a wire makes it more difficult for a power source to reach all the accessories that it needs to. An extreme example would be a tractor and trailer, with all its lights on. All it’s accessories like wipers, radio, not to forget the engine itself. And every single electrical component is connected by a 2 gauge ‘welding cable’. For the batteries to complete such a large and exaggerated circuit would be an extremely heavy load. The strain would find itself on the batteries and the alternator.

Choosing too small of a wire is asking for problems. Best case scenario and a marker light aren’t quite as bright as they could be. Worst case scenario an electrical sensor isn’t able to send the proper signal back to the ECM controlling the engine and an engine runs inefficiently. Or not at all. But also problematic and possibly much more dangerous for the people involved, putting too much burden on too small of a wire or cable could cause a wire to overheat which can lead to electrical fires.

The middle ground is a big one. An incandescent light system could typically use wire gauges 8-20 and none would be the wiser. If there were any problems, few could probably tell. In a starting system, one could use anywhere from 4 to 4/0 and could probably get away with it. At least for quite a while. That being said, good enough rarely is and we are talking about the equipment we rely on to make a living. So here are some tips to make wire and cable selection easier.

1- When in doubt, err on the side of a slightly larger gauge. If your trailer’s lighting system came to the world with 14 gauge, you will be okay with 12. One size up is not able to cause any problems and a now older system will benefit from having a better flow of electricity. As a starting point, wire gauges are available to know what is on your unit. If you’re taking apart wiring before getting the new wire, your skinners will be able to reliably do the job of showing what gauge you are working with.

2- Keep in mind that that gauge selection is based on amperage and distance. 1 amp over a foot takes next to nothing for reliable transmission. 100 amps over 50 feet require a lot more capacity. And remember rule number 1. You’re better off erring just slightly larger, than smaller. This can be made difficult by the rising price per foot or cable as gauges increase in size.

3-When in doubt, get informed. If you’re presented with a situation where you feel unconfident to make a decision, refer to the manufacturer or take measurements of amperage and distance and refer to one of the many available charts online. Most of these charts are free and reliable.

Conclusion

Choosing the right gauge is important. The downside to getting it wrong doesn’t have to be a big deal, but it can be dangerous. Being informed is really important. I hope this information along with these tips will, at a minimum, make your next ‘best guess’, a little better.

Drive safe,

Kevin Gauthier