circuit sizing and current

[djd]

690.8 [a] 1 says parallel module short circuit currents multiplied by 125 % , what do they mean by short circuit current and where do you find that sum . short circuit I think of aic rating , I dont think that applies here. any help would be greatly appreciated .

 

[jaggedben]

Short circuit current is a module spec provided on the datasheet and module label.

 

[ggunn]

Imax = Module Isc X number of parallel strings X 1.25

 

[ggunn]

Short circuit current is a module spec provided on the datasheet and module label.

aka Isc

 

[djd]

Thanks I over complicate as usual , still like to know why its refered to as short circuit current.

 

[jaggedben]

Thanks I over complicate as usual , still like to know why its refered to as short circuit current.

It's the current you get if you expose the module to standard test conditions* and short the positive and negative leads. It's really the same concept as with other sources, just typically smaller amps.

*standard test conditions for solar modules are 1000W/m^2 irradiance and temperature of 25C.

 

[Carultch]

Thanks I over complicate as usual , still like to know why its refered to as short circuit current.

Short circuit means the load resistance (or more generally, impedance) connected across the terminals of the source is zero or close to it. Generally considered bad practice to let any circuit get to this condition, as the high amounts of current could damage the components. Solar modules are unusual, in that the short circuit current is close to the typical operating current, unlike your utility power source where a typical 200A service has kiloamps of short circuit current. The opposite is called an open circuit, where the source isn't connected to anything, with effectively infinite impedance across the terminals. No matter how high the voltage in an open circuit, current will not flow.

 

[ggunn]

The point of the article is to direct you to size the conductors such that even a dead short will not damage them. You do the same with inverter output circuits. All the OCPDs in solar are there to protect the conductors from fault current coming from the other direction.

 

[Zee]

Imax = Module Isc X number of parallel strings X 1.25

fine point:
only multiply by number of parallel strings if they are combined into a single output circuit.

some people take parallel to mean parallel in conduit....... and some to mean parallel wired (combined) together.

e.g. if you have 3 circuits going to inverter independently..... then it is just Solar Panel Isc x 1.25.

 

[ggunn]

fine point:
only multiply by number of parallel strings if they are combined into a single output circuit.

some people take parallel to mean parallel in conduit....... and some to mean parallel wired (combined) together.

e.g. if you have 3 circuits going to inverter independently..... then it is just Solar Panel Isc x 1.25.

True enough, but I was just trying to help the OP interpret 690.8(A)(1).