The Waytek Blog

When Do You Need GPT Primary Wire? 

Automotive GPT primary wire is the most widely used wire for automotive projects and electrical wire connections. 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. Think of GPT wire as a general circuit type of wire intended for standard electrical wiring usage in vehicles. Avoid using it next to the engine or in areas that are subject to exposure to liquids or environmental elements.

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. The cross-link wire offered at Waytek also features a smooth surface finish and is highly resistant to moisture, grease, oil, gasoline, and 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. 

To learn more about the variations in the two main automotive wiring types, see the article How to Choose Between Automotive Cross-Link and GPT Wire.

Understanding Wire Gauge

Wire gauge—the measurement of the diameter of the wire—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. An 8 gauge wire, for example, is thicker and heavier than an 18 gauge wire. Wire is typically labeled or referred to with a gauge number followed by “Ga.” or “AWG” (AWG stands 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%, the efficiency of the equipment in the circuit is severely decreased and the life of the equipment will be shortened. As wire lengths get longer, electrical resistance builds up until it forces the voltage down below a usable level. If the wire length results in too much voltage drop, upsizing the wire gauge can 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 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. 

Waytek also offers our own handy slide rule (shown at right) to enable quick determinations of wire gauge in relation to amps and wire length in 24-volt applications. Order a Waytek wire selector slide rule.

Disclaimer: Many factors can affect the performance of an application, such as voltage, temperature, load, etc. Please refer to your design engineer for final decisions.