How To Calculate Circuit Breaker In Solar Pv System

Two standard pv breaker examples.

How to calculate circuit breaker in solar pv system.

1 35 times because wires are designed to carry over load current. Thunb rule to calculate design of circuit breaker of fuse is 1 04 1 35 rated current. So manufactures do not supply these with their inverters. There is a code rule nec 690 64 b 2 that s says you must not exceed a certain size circuit breaker for solar.

3 follow the code. Now these are often included with some inverters but it s a good idea to check. A 3 poles circuit breaker can be used on 3 phase system using either 2 or 3 poles. So for example if you have a 200a service you cannot install more than 40a of solar circuit breakers 200 0 2.

A maximum output current of 22a multiplied by a 125 percent safety factor equals 27 5a. The nominal load current of the circuit breaker is calculated as. A single phase circuit breaker can t be used for three phase supply voltage levels. Ibn 40 a x 0 9 x 0 77 x 1 07 29 7 a.

So we assumes that rated current can be 1 3 times more than flows in some condition that can beared by wire without insulation damaged. So use a 20a circuit breaker. To calculate the fuse size required between the string and the inverter s dc input you take 9 12 x 1 56 14 7 and round up to the next trade size of 15a. A maximum output current of 16a multiplied by a 125 percent safety factor equals 20a.

However if we add our pv breakers into a sub panel that is dedicated to only the pv breakers we can land the sub panel into a 40a breaker in the main panel board 10 4a 21a 31 4a x 1 25 39 25a. 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. This happens to be a standard breaker size. Multiply the nominal watts of the solar panel by the numbers of hours of sunshine it is exposed to.

This is defined as 20 of the overall home s service rating. When sizing this combined fuse breaker we must first determine the worst case current that will flow based on our specific panels.