In a solar system, several main components often require fusing for safety and protection against overcurrent situations. These components typically include:
Here's a step-by-step guide:
Solar Panels
Each solar panel or string of panels connected in series should have a fuse or a solar panel combiner box with fuse/circuit breaker protection. Fusing the solar panels helps prevent damage due to overcurrent caused by factors such as shading, a faulty panel, or a short circuit. For example, if you have 3 strings of panels capable of 10 amps per string that is potentially 30 amps being drawn to single panel if it is shorted. To determine if your solar panels need to be fused:
- Determine the max fuse rating of the junction box installed on your solar panel. This can be found on the panel label or on the datasheet. Most panels are between 15A-20A.
- Determine the ISC amp rating of the solar panel and the number of strings in your array.
- In series strings, the volts are added, while the amps remain the same. If each panel is rated for 10 amps, a single string will produce 10 amps regardless of there being 1 or 5 panels in the string.
- Take the amp rating of a string and multiply it by the number of strings. So, if each string is 10A and there are 3 strings the total is 30AMPS. Multiply this number by 1.25A for safety purposes. 30A x 1.25 is 37.5A.
- Compare this number to the max fuse rating of the panel. If the total amps of all strings exceed the max fuse rating of the panel, then it needs to be fused.
- To simplify the process, you can choose a fuse equal to the max fuse rating of the panel. If the max fuse rating is 15A then use a 15A fuse for each string.
- MC4 inline fuses are typically used for this application or a combiner box with a circuit breaker for each string.
Charge Controller
The charge controller is responsible for regulating the charge to the battery bank, should have a fuse/circuit breaker for protection. This protects both the charge controller and the battery bank from excessive current that could damage them. To determine the proper fuse/circuit breaker:
- First consult the manufacturer’s manual. This should always be the first step when installing solar equipment.
- If there is no manufacturer recommendation find the max amp output rating of the solar controller.
- You typically want the protection to be about 20-25% higher than the max output, rounded up to the next available size. This protects the device while avoiding nuisance trips.
- As an example, if you have an 80A charge controller, multiply 80A x 1.20 and you get 96A. You would then round up to the next available size fuse/breaker which would be 100A.
- You want to install this on the positive between the charge controller and the battery bank.
Battery Bank
Fuses are necessary to protect the battery bank from overcurrent or short circuits. Each battery bank should have an individual fuse or a fuse located at the positive terminal of the battery bank. This protects against potential hazards like battery failures or accidental short circuits.
- First consult the manufacturer’s manual. This should always be the first step when installing solar equipment.
- If there is no recommended fuse size, determine the maximum current that the battery bank can deliver safely.
- Choose a fuse with a rating slightly higher than the calculated maximum current to ensure it can handle the peak current without blowing unnecessarily. It's common to select a fuse with a rating around 1.25 to 1.5 times the maximum calculated current to provide a safety margin.
- If your battery bank can deliver 100A, then 100A x 1.25 gives you a fuse rating of 125A.
- Select a fuse type suitable for use in a battery bank application. Typically, fast-acting fuses or circuit breakers designed for DC applications are used to protect battery banks in solar systems. These fuses are designed to interrupt the circuit quickly in the event of an overcurrent situation to prevent damage to the batteries and other components.
Inverters
Inverters, which transform the DC power from the batteries into usable AC power, should also be fused. Fusing the inverter protects it from excessive current and potential damage. It also ensures the safety of the electrical system connected to the inverter
- First consult the manufacturer’s manual. This should always be the first step when installing solar equipment.
- If the fuse size is not listed in the documentation, contact the manufacturer directly.
- If none of these methods work calculate the size of the fuse/breaker by the watts and DC volt rating of the inverter.
- For instance, if you have a 2500W inverter that is 24V use the following formula:
- Watts / Volts X 1.25 and then round up to the next available size fuse/breaker.
- 2500W / 24V x 1.25 is 130A. Rounded to the next fuse/breaker would be 150A.
- Ensure that the selected fuse is suitable for DC applications and compatible with the wiring and terminals used in your system. Install the fuse in series with the positive terminal of the battery bank and the positive input terminal of the inverter, following the manufacturer's guidelines.
Our next blog will go over how to properly size the wire for these solar components.