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How to Select the Right Wire

Posted by R. Iversrud on Apr 20, 2020 12:59:01 PM

The wiring you select for your applications and maintenance of electrical systems is an integral part to keeping your system operating as designed. There are many types of automotive wire, understanding which types are best suited for your application can be confusing. 


For this reason, we will focus on wire typically used in automotive applications and cover two main insulated Wirewire types, such as automotive GPT primary wire and cross-link wire, as well as covering the importance of wire gauge size based on your application, current draw, potential electrical resistance, and voltage drop.

When Do You Need GPT Primary Wire?

Automotive GPT primary wire is the most widely used wire for automotive projects and electrical wire connections. Why? It has a single conductor, stranded bare copper, jacketed polyvinyl chloride (PVC), and an excellent resistance to oil and flame. Plus, its smooth surface is ideal for threading and pulling through wire looms or conduits.

When Do You Need Cross-Link Wire?

Cross-link automotive wire is constructed with chemically altered polyethylene insulation, making it more durable and resistant to heat than standard GPT automotive wire. Our auto wiring features a smooth surface finish and is resistant to moisture, grease, oil, gasoline, as well as most acids and solvents. This durability means cross-link wire is typically found in high temperature areas, such as connecting wiring to circuit protection devices in engine compartments or automotive wiring connectors

What Is a Wire Gauge?

A wire gauge is a measurement of the diameter of the wire. This size determines the amount of current your wire can safely carry. The wire gauge also tells you the weight and electrical resistance of the wire.

The smaller the wire gauge number, the heavier the wire; and the larger the gauge number, the lighter the wire. Wire is typically labeled or referred to with a gauge number, followed by “AWG.” These letters stand for “American Wire Gauge.”

The most common wire gauge sizes seen in automotive applications include 18,16,14,12,10 and 8 gauge.

How to Select the Right Wire Gauge

To find the right wire gauge, you need to know the current voltage drop. Voltage drop is the amount of voltage lost over the length of the wire or cable. 

Voltage drop changes as a function of the resistance of the wire and should be less than 2% if possible. If the drop is greater than 2%, efficiency of the equipment in the circuit is severely decreased and life of the equipment will be decreased. As wire lengths get longer, electrical resistance builds up until it forces the voltage down below a usable level. At that point, up-sizing the wire gauge will restore the voltage to its intended level.

How is voltage drop calculated? Ohm’s Law states that current through a conductor between two points is directly proportional to the potential difference across the two points. That is a very long way of saying, Voltage Drop = current in amperes x resistance in ohms.

Depending on the calculated voltage drop, you should be able to find the right wire size. If you don’t want to do the math, our partner, Blue Sea Systems, has created an interactive Circuit Wizard that helps you find the correct wire size.

Blue Sea Systems has also created a printed version of the calculator that can be a helpful resource tool. This 20x17 convenient desk mat (pictured below) allows for quick calculation of needed wire gauges. Although this guide is titled “Protect your boat with the correct size wire, fuse and fuse holder”, it can be used for all mobile vehicle applications. As the title notes, this helpful desk mat also provides a fuse selector.

Click here to receive this desk mat for free! 

Blue Sea Deskmat

Disclaimer: Many factors can affect the performance of an application, such as voltage, temperature, load, etc. With so many variables, Waytek is providing this wire gauge guide as a general guideline only. Please refer to your design engineer for final decisions.

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