olar systems are no less safe than any other of your electric appliances, but this is no excuse for neglecting the most basic safety measures. Today, we will focus on solar panel fuses to help you understand whether they are necessary for your particular case.
What are solar fuses?
A solar fuse is a kind of fuse explicitly designed for PV power systems and used to protect their wiring from an electrical malfunction and catching fire. It helps avoid issues like overcurrent – a situation when the current in the circuit rises sharply and far exceeds the nominal amperage capacity of that circuit. And if that happens in a PV system, a fuze interrupts the current, thus protecting the wiring and the panels.
A fuse is a two-terminal device consisting of a metal strip or wire element with a very low melting point. When excessive current flows through the element, it melts, thereby stopping it.
Does my solar system need a fuse?
The necessity of equipping your solar installation with fuses depends on its wiring type. Like a battery, each solar module has two terminals; the positive and the negative. A series connection is made by connecting the positive terminal of one module to the negative terminal of the next module. In this wiring type, the voltage increases while the amperage (current) remains the same. Suppose you have six solar panels rated at 12 volts and 5 amps wired in series. In that case, the entire solar array would be 72 volts at 5 amps.
Wiring solar modules in parallel connects all the positive terminals together and all of the negative terminals together. Parallel wiring causes the amperage to increase, but the voltage doesn’t change. So if we connect six solar panels rated at 12 volts and 5 amps in parallel, the voltage will remain at 12 volts, and the current will increase to 30 amps.
According to the overcurrent protection rules specified in the National Electric Code (NEC), solar modules wired in parallel require fusing, except when the short circuit current of the entire PV array is lower than the maximum series fuse rating of a module (maximum fuse size that can be used).
In other words, solar fuses aren't necessary if your panels are connected in series. With only two strings in parallel, fusing isn’t required as well. But with three or more strings in parallel, you do need fuses for overcurrent protection.
Where exactly should the fuzes be placed?
At least three places in a solar power system should be fused. The first is between the panels and the charge controller in a combiner box. This box connects several strings in parallel and combines output currents from multiple strings for connection to the charge controller or grid-tie inverter. Each string lands on a fuse terminal within the combiner box, after which the output merges into a single cable connected to the charge controller.
Apart from that, fuses are usually installed between the battery and the inverter as well as between the battery and charge controller: they protect the inverter and the charge controller from damage and the battery from a possible explosion.