Does max series overcurrent protection limit apply?

[Bluedog225]

I’d appreciate some help understanding the limitation regarding the maximum series overcurrent protection.

Specifically, does this limit not apply when no overcurrent protection is needed?

For example, I’d like to run 12 panels, 6 in series and 2 strings parallel. VOC will be 240 volts and the combined strings will be 19 amps.

With 2 strings, no overcurrent protection required.

Do I need to be concerned about exceeding the 15 amp limit in this scenario?

Thanks

Max. Series overcurrent protective
device (where required) fuse rating Standard test condition	[A] 15

 

[hwy17]

I interpret that as saying if you're going to run 3 or more strings in parallel, each string needs an OCP of 15A or less. I.e. don't run 3 strings with 20A OCP per string.

2 strings without OCP is still allowed.

 

[mikefitz]

exceeding the 15 amp limit in this scenario

That's 15 amps per panel or a string of those panels. With two strings in parallel, technically no series fuse is needed, unless local code requires fuse protection regardless. ( if one of two parallel strings were to fail, the maximum fault current would be 9.5 amps, thus the 15 amp fuse would offer no protection).

 

[robbob2112]

Ignore me, I am not so smart sometimes - takes 3 to need the fuse.

Were it me I would pop a MC4 15amp fuse on each string before they are joined in parallel. This covers you in case there is a fault in one string.

it is NOT technically required. with only 2 strings to fuse them.

Make sure if you are using the Y combiner cables they are #10 or #12 wire in them. I would do #10 since the #12 is only good to 20 amp and you are right there at the max.

 

[mikefitz]

This covers you in case there is a fault in one string

Please explain which current source, In excess of 15 amps, exists in a two string set up?

 

[robbob2112]

uhm uhm uhm...

Thinking hard...

ok, you got me, it takes 3 to tango and exceed 15 amps on the one if there is a fault.

 

[wdwtx2.0]

Fuses are cheap insurance.
Probably never pop one, but if you do, it was worth it.
I fuse each string.
I use the MidNite Solar Midget fuse holders.

 

[Bluedog225]

It’s an interesting question whether an inline fuse where none is needed reduces or increases the chance of fire.

 

[timselectric]

It’s an interesting question whether an inline fuse where none is needed reduces or increases the chance of fire.

It adds 2 or 4 connections. Which provides the same amount of possible hot spots or failure points.
The least amount of connections is always the best option.

 

[dopeassjackson]

Series pannels add voltage not amps in this situation. And no 2 or 3 strings in series dosnt matter for the amp capacity of your pannels. No amps should be going from one string to another because you need a load to use amps.

 

[timselectric]

Series pannels add voltage not amps in this situation. And no 2 or 3 strings in series dosnt matter for the amp capacity of your pannels. No amps should be going from one string to another because you need a load to use amps.

A shorted string is an infinite load to all other strings in parallel with it.
This is what the "maximum fuse size" on the solar panel sticker is referring to.