Questions About Over-Current Protection Devices (OCPD)

[rjolicoeur]

I have several questions about over-current protection. I’ve included a diagram of the array I’m planning at the bottom of this post.

• All the MC4 style fuses that I’ve found online have a 1,000 V DC rating. As long as the amperage rating is correct, would a 1,000 V DC fuse work for an array that only generates around 120 V?
  
  
• All the DC circuit breakers I see online have lower voltage ratings (12V, 24V, 48V). Would they work in an array that generates around 120 V?
  
  
• For a 4S3P array, does the Isc amperage of the individual PV panels in the series connection determine the fuse size required?
  
  
• In my case, each of the four panels in one of the series connections have an Isc of 5.21 amps. Would a 10-amp fuse be the correct choice?
  
  
• Should the fuses be located at the point where the positive leads become a parallel connection?

Thank you for your assistance!!!

 

[12VoltInstalls]

All the MC4 style fuses that I’ve found online have a 1,000 V DC rating. As long as the amperage rating is correct, would a 1,000 V DC fuse work for an array that only generates around 120 V?

Yes. Just like you don’t have to fill a 2-gallon pail- it works as good with a quart in it- you don’t have to put 1000V through a 1000V-rated fuse for it to work.

All the DC circuit breakers I see online have lower voltage ratings (12V, 24V, 48V). Would they work in an array that generates around 120 V?

No. Not unless rated in excess of the volts you are applying.

For a 4S3P array, does the Isc amperage of the individual PV panels in the series connection determine the fuse size required?

You will need to properly fuse each 4S string. In series, the max amps of the string is the same as a single panel.

In my case, each of the four panels in one of the series connections have an Isc of 5.21 amps. Would a 10-amp fuse be the correct choice?

I might pick 7 or 8 but 10 is fine if the maximum fuse rating is high enough

Should the fuses be located at the point where the positive leads become a parallel connection?

That is where I would put them. Many use a combiner box for that.

View attachment 139658
Thank you for your assistance!!!

 

[rjolicoeur]

Thank you again! Your response put me on the right track. I went back & reviewed a post about OCPD on explorist.life and it finally made sense to me.

Without the help from the members here on this forum, I would have made some serious mistakes.