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What Size Cable for 12v Solar Panel?

By Benjamin Strusnik June 17, 2022

Our mission here at Shop Solarkits is simple: to make solar energy easy. That means easy to understand, user-friendly, and affordable. Today we address a common question. What size cable to use for a 12v solar panel.

What Size Cable to Use for a12v Solar Panel

Differences in Size

Different solar systems need different wire sizes. Even different parts of a solar system may need different sizes. 

Solar power usually needs a 12 gauge AWG wire. But as the size may differ depending on resistance and flow, you need to determine the amps to know which size you need. 

Standardized Sizes 

Solar wires sizes are standardized using the American Wire Gauge (AWG). Wires with higher numbers generally have more resistance and can deal with lower currents only.

what size wire to use for a 12v solar panel

Metals 

For most installations, aluminum or copper solar wires are used. 

Copper wire has far better conductivity and carries more current than an aluminum wire of the same size. It offers flexibility and better heat resistance.

Understanding Cable Terminology

Voltage

The voltage represents the potential electric potential energy of your solar panel per unit charge. Your solar panel’s peak power voltage is measured in volts and watts and is expressed as voltage maximum power or VMP.

Voltage Drop Index

A reduction in voltage causes a loss of power (V=IR) and an undersized wire can cause this reduction. This is represented with a voltage drop index.

Rated And Maximum Current

Electrical current flows between the electrical circuits and is measured in amps.  The rated current is the maximum that can be drawn in continuous use, without reducing the longevity of the solar panel.

Formula for Cable Size

When you invest in a DIY solar kit you’ll find that it includes almost everything you need. But with most technology, there’s a formula to determine what size cable you need. 

what size wire to choose for a 12v solar panel

Even if you are not outstanding at maths, you’ll find the calculation fairly simple. The formula is Amps = Watt / Volt. 

How the Formula Works

Whether you’re installing solar panels on a boat or the roof of your home, the formula remains the same. If you know the watts and voltage of your system, you can find the amperage.

The amps will determine the minimum AWG cable size to use, based on a 2% voltage drop. In this case, you know that the voltage is 12V. Divide the wattage of your solar panel by the voltage to determine the amps. 

Why Amps Are Important

Most often, you will need a cable gauge between 10 and 14. But a 14 gauge solar wire can only handle a maximum of 15 amps. And many solar panels need a higher amp. 

When you are unsure of the amps, a 12 AWG cable may be the best bet. This is because a 12 AWG cable has an amp capacity of 20 with a 2% voltage drop.

Cable Length

Once you’ve determined the amps, you can choose the best gauge. But there is more to choosing the right cable than the diameter. Length also plays its part. 

This is because the longer the cable, the higher the voltage drop. You need to factor this into your calculation. Longer cables may not always be feasible in smaller spaces, for example when installing solar panels on a van. 

Why Cable Size Is Important

Every wire gauge (AWG) has a maximum current limit that the cable can handle before damage occurs. It is crucial to pick the correct size so that the cable does not overheat. 

what size cable to use for a 12 v solar panel

Risk of Overheating 

Solar panels harness the sun’s energy and transform it into electrical current. Just like batteries, a solar panel has positive and negative terminals. And current flows from the negative terminal to the positive terminal.

Wires then transport this current to your electrical units. If too high a current is run through them, there’s a risk of overheating from too much energy. In certain jurisdictions, undersized wires and cables constitute a violation of the National Electric Code.

What Size Cable for 12V Solar Panel FAQ

Can I mix different wattage solar panels?

Although mixing different wattage solar panels is possible, it reduces the efficiency of your solar energy system. 

Can I use two charge controllers for one panel?

While you can use two charge controllers for one solar panel system, each controller must have its own solar panel block.

what size wire to choose for a 12 v solar panel

Closing Thoughts

Solar energy is renewable, safe, and simple when used correctly. 

But choosing the right wire size is essential for the safety and functionality of your solar panel. By following the guidelines and formula above, you’ll select the right cable size with confidence.

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