Fuse/Breaker Sizing?

[mrsolar]

Hello again Solar Panel Talk,

You have been a great source of informative and helpful advice to me since I first started frequenting this board a few months ago.

I come to you today with a question relating to how to size breakers/fuses for a Solar Panel Array that is in 6 strings with 5 modules giving a total amperage of 15.46a and 544v (after Isc multiplication of 156% and Voc temperature adjustment). My question is what is the safest fuse size to use for this setup in a combiner box and ? How did you come to your conclusion of sizing the fuses?

[Sunking]

Consult NEC 240, 310, and 690

[paulcheung]

Are you sure the numbers you give is right? 6 strings only give you 15 amps? less than 3 amps each string? and 5 panels give you 544 volts? 100 volts each?

[Naptown]

Are you sure the numbers you give is right? 6 strings only give you 15 amps? less than 3 amps each string? and 5 panels give you 544 volts? 100 volts each?

He has amorphous panels if i remember correctly High voltage and low amperage

[paulcheung]

ok Thanks

[mrsolar]

Hi team, spent a few days researching this issue and there are many verdicts but the one that sounds most correct is Isc x 125% or x 156% for fuse/breaker sizing. DC fuses are different from AC fusing, arc quenching sounds like a dangerous factor to choosing the right fuse, therefore I'd recommend a good quality manufactured fuse/breaker such as Eaton. Thanks for your input so far.

[mrsolar]

Also for transformer isolating inverters you will need a DC breaker or isolator that is double pole (breaks negative and positive simultaneously) and is rated to break 1.25 x the Short Circuit Current (Isc) rating of the solar PV array AND 1.2 x the Open Circuit voltage (Voc) of the array.

Generally speaking, breakers and isolators suitable for Solar PV are not available in tight sizes, but rather some common jump points are:

DC Current: 8A, 10A, 16A, 20A, 25A, 32A

DC Voltage: 250V, 440V, 500V, 800V and 1000V

[Naptown]

Hi team, spent a few days researching this issue and there are many verdicts but the one that sounds most correct is Isc x 125% or x 156% for fuse/breaker sizing. DC fuses are different from AC fusing, arc quenching sounds like a dangerous factor to choosing the right fuse, therefore I'd recommend a good quality manufactured fuse/breaker such as Eaton. Thanks for your input so far.

Incorrect fuse size is isc x 1.25. The conductors are calculated by using the 156%
FWIW I tend to fuse closer to the ISC than that.

[mrsolar]

Incorrect fuse size is isc x 1.25. The conductors are calculated by using the 156%
FWIW I tend to fuse closer to the ISC than that.

Thank you Naptown.