When electricity enters your home, it goes to a circuit breaker box (or fuse box in older homes), where it's divided into a number of circuits. Each circuit is protected by a breaker or fuse. Bedrooms, living rooms and family rooms where only lights, alarm clocks and other small electrical items are usually used are normally onKitchens, laundry rooms, bathrooms and dining rooms—places where you're more likely to use toasters, irons, hair dryers and other big-watt items—are usually served by heavier-duty, 20-ampMajor appliances like 5,000-watt electric water heaters and 10,000-watt electric ranges demand so much electricity that they take their own 30- to 50-amp dedicated circuit (See Fig. D in “Additional Information” below), protected by big, “double The circuit breaker, the wire and even the wire insulation are all designed to work as a system—and that systemTry to push more current through a circuit than it's designed for and things start happening

Wires heat up under the burden of carrying theWhen this happens, the insulation around the wire can degrade or even melt. melts, current is no longer confined within theThat's when fires start. Luckily, the circuit breaker senses the excess current and “trips” to stop the flow of On the night the lights went out at your house, you were fine with only the lights and coffee maker operating. clean|power to the people Sign up for our Newsletter How to properly fuse a solar PV system NOTE: If you are unsure about this area, consult an electrician. Proper use of fuses and breakers are important to maintain safety. The first thing to know is that fuses and circuit breakers are primarily used to protect the system wiring from getting too hot and catching fire. Secondly, they also are used to protect devices from catching fire or from becoming more seriously damaged if there is a short circuit. A good example is a 12V lead acid battery. If a short develops in your AC/DC inverter for instance, a fuse between it and the battery will prevent a possible explosion of the battery and it will cut the circuit fast enough to prevent the wires from catching fire or getting dangerously hot.

In this case, the battery, wires, and AC/DC inverter will be safely disabled by the fuse. Solar Panel fusing Commercially made solar panels over 50 watts have 10 gauge wires capable of handling up to 30 amps of current flow. If you connect these panels in series, there will be no increase in current flow so fusing is not required for this string. This is not the case when you have panels connected in parallel, as when connected in parallel the system current is additive. Bathroom Vanity With Attached MirrorFor instance if you have 4 panels each capable of up to 15 amps, then a short in one panel can draw all 60 amps towards that short-circuited panel. Vinyl Tile Backsplash SheetsThis will cause the wires leading to that panel to far exceed 30 amps causing that wire-pair to potentially catch fire. Trained Labs For Sale In Missouri

In the case of panels in parallel, a 30-amp fuse is required for each panel. If your panels are smaller than 50 watts, and use only 12 gauge wires, and 20 amp fuses are required. Parallel/Combiner Box fusing In a parallel system a combiner box is used that holds the fuses/breakers to each panel, plus one or more “combined” fuse leading to the charge controller or grid tie inverter (see figure). When sizing this “combined” fuse/breaker, we must first determine the worst case current that will flow based on our specific panels. If we take the example 144-watt 12V panel from the introduction section, and look at the short circuit current (Isc), we see it is rated at 8.5 amps. This however can be exceeded if the actual installed situation does not match the “standard” test conditions used for solar panel factory ratings. The industry rule is to increase Isc by 25% to cover this possibility, so it now is 10.625 amps in our example. The National Electrical Code (NEC) also requires that a 25% factor be added if the load is continuous, so the number grows again to 13.28 amps per panel.

If there are 4 panels in this parallel set, then the combined current can theoretically be as high as 53.125 amps. The chart below shows the ampacity for wires in a conduit per the NEC. Note that some wires of the same gauge can handle more amps and higher temperatures. An 8 AWG USE-2 wire set (minimum) from the combiner box to the charge controller in our example will suffice, since it can handle 55 amps. A 60-amp fuse or breaker should be used in this case to protect this wire set. This also aligns with the maximum capacity of the charge controller selected. Charge controller to Battery Fuse/Breaker With a Pulse Width Modulated (PWN) charge controller, the worst-case amps flowing to and from the controller are the same, so the fuse and wire size can match. MPPT charge controllers, on the other hand, are able to both lower the voltage and increase the current flowing between the controller and the battery bank, so the exact size wire and fuse size must be recalculated or obtained from the charge controller manual.

As an example, Blue Sky recommends a 60-amp fuse/breaker for their Solar Boost 50 (amp) charge controller between the unit and the battery bank. Again, select a wire that is rated appropriately. Battery Fuse/Breaker to Inverter The wiring and fusing from the battery to an AC/DC inverter is of critical importance because this is where the most current will likely flow. Similar to the charge controller case, the recommended wire and fusing should be obtained from the inverter manual. It is very likely the invert already has a built in fuse/breaker on the input as well as the output (AC) side of the unit. A typical 1500-watt 12V pure sign wave inverter draws up to 125 amps continuously, a number that increases to 156 amps once we factor in the NEC continuous-use 25% adder. For USE-2 wires, 1/0 AWG is required in this case. For a hobbyist, welding cable is generally used with these general limits: #4 AWG 150 amps #2 AWG 200 amps #1 AWG 250 amps 1/0 AWG 300 amps 2/0 AWG 400 amps Final Note: This article was just an introduction.