Fuses and Wire Gauge
Size a Fuse
Adding a fuse is extra protection for your system. It is meant to protect from system over-voltage or damage from a short circuit. It is not mandatory to have fuses for your system to function properly. However, we do recommend to add fuses to prevent any mishaps. We recommend adding two different fuses in the following scenarios:
- Between the charge controller and battery bank (ANL Fuse Set + Fuse)
- Between the charge controller and solar panels (Solar Connector Inline Fuse)
- Between the battery bank and inverter (ANL Fuse Set + Fuse)
SOLAR CONNECTOR INLINE FUSE (Model: RNG-CNCT-FUSE)
ANL FUSE (Model: RNG-SET-ANL)
When hooking up your Renogy system, the best way to add protection is by using fuses or circuit breakers. Fuses and circuit breakers are used to protect the wiring from getting too hot and protect all devices connected in the system from catching fire or getting damaged if a short circuit occurs. They are not necessary for the system to run properly, but we always recommend using fuses or circuit breakers for safety purposes. There are three different locations that we recommend installing fuses or breakers:
- Between the charge controller and battery bank
- Between the charge controller and solar panels
- Between the battery bank and inverter
Between the charge controller and battery bank
To determine the fuse size needed, simply matching the rating on the charge controller. For instance, if you have one of our 40Amp charge controllers, we recommend using an 40Amp fuse between the controller and battery. This will help protect your system if you decide to connect the maximum power to the controller. In addition, it is mindful to use appropriate wiring that can also support the maximum continuous amps for this rating as well for further safety.
Between the solar panels and charge controller
The size of this fuse is dependent on how many solar panels you have and how they are connected (series, parallel, or series/parallel). If the panels are connected in series, the voltage of each panel is added but the amperage stays the same. And for the amperage of the panel, you will need to check the rated short circuit current (Isc) value for the panel your are using. The short circuit current (Isc) is the largest current that the solar panel can produce under any circumstances.
For example, if you have two 100W panels connected in series, each producing 20 volts and the rated short circuit current (Isc) is 5 amps, the total output would be 40 volts and 5 amps. We then take the total amperage and multiply it by a safety factor of 25% (5A x 1.25) giving us the fuse rating of 6.25A or 10A if we round up to the nearest available fuse size.
Series Volts = V1+V2: 20V + 20V = 40V
Series Amps = (A1 = A2) * Safety Factor (1.25) = 5A * 1.25 = 6A Rating or close value
If the panels are connected in parallel, the amperage of each panel is added up, but the voltage stays the same.
For example, if you have two 100W panels connected in parallel, each producing 20 volts and the rated short circuit current (Isc) is 5 amps, the total output would be 20 volts and 10 amps. We then take the total amperage and multiply it by a safety factor of 25% (10A x 1.25) giving us the fuse rating of 12.5A or 15A if we round up to the nearest available fuse size.
Parallel Volts: V1= V2 = 20V
Parallel Amps: (A1 + A2) * Safety Factor (1.25) = (5A + 5A)* 1.25 = 12.5A or close value
Between the battery bank and inverter
The last fuse would be between your inverter and the battery bank. Proper wiring size and fuse sizing is critical for inverter application, given their high amp draw nature. A fuse size recommendation is usually stated in the manual and most inverters already have built in fuses/breakers. However, it is always good practice to add more overcurrent protection. The rule of thumb that we use here would be the inverter rating divided by the battery voltage. This value is then multiplied by a safety factor.
For example, let’s consider our Pure Sine Wave Inverter is rated for 1000Watts and will be connected to a 12V battery bank. You want to divide the Inverter Watts by the Battery Voltage AND ALSO the efficiency rating of the inverter. In this example we will consider a 1000W inverter with a 90% efficiency and a 12V battery bank:
Fuse Recommended = Inverter Watts / Battery Bank Voltage / % Efficiency
= 1000W / 12V / 0.90
= 92Amps Continuous
We then multiply by the 25% safety factor (1.25):
= 92Amps (1.25)
Fuse Recommended = 115Amp or close
We can consider the nominal battery voltage (12V) to be the minimum continuous amps, as the value can increase when applying a low battery voltage and a safety factor. Therefore, when selecting which wire gauge to connect to the inverter it is also important to consider the continuous amps. The chart below shows the ampacity for wires in a conduit per NEC Table
Wire Gauge
When selecting which wire gauge to connect use it is also important to consider the continuous amps. The chart below shows the ampacity for wires in a conduit per NEC Table
Considering the NEC for the 3 situations:
1. Between the charge controller and battery bank
If you are connecting and expecting 40A from the controller to the battery bank, A 8AWG copper wire with 90C insulation is rated for 55A and would work in this application as you would want to oversize for protection.
2. Between the solar panels and charge controller
If you have 2 panels in parallel and expecting 10-12Amps from the panels to the controller, a 14AWG copper wire with 90◦C insulation is rated for 25A and would work in this application as you would want to oversize for protection.
3. Between the battery bank and inverter
If you are connecting and expecting about 92Amps from the battery bank to the inverter, A 4AWG copper wire with 90C insulation is rated for 95 Amps and would work in this application as you would want to oversize for protection.
For details on how to size a wire in a power system, see Sizing Wires for PV Systems.
NOTE:
This is a brief introduction and summary for fusing selecting wire gauge for your system. There are other factors such as cable length, voltage drop, and fuse/breaker types that could be considered depending on the application. We recommend giving us a call for more information!
