MC4 Inline Fuse Placement and Size Question for Series+Parallel Combo

[Off Grid/Off My Rocker]

Hello Everyone,

I am going to build the following solar array for an off-grid cabin in northern Spain and had two specific questions regarding the use of MC4 Inline Fuses. I have attached the diagram of the system I plan to build below.
First Question: In this system set-up do I install the MC4 Inline fuses right before the Positive (red) Branch Connector (3 series so one fuse per positive line? or do I need fuses elsewhere too?)
Second Question: The panels I am planning to use have a Maximum Series Fuse Rating of 25A. I've only every come across MC4 inline fuses in 5A, 10A, 15A, 20A, and 30A sizes. Would I use the 20A size fuse for this application to be under the 25A maximum?

Thanks so much for all your help! Total novice here
Glenn

 

[timselectric]

right before the Positive (red) Branch Connector

This

Would I use the 20A size fuse for this application to be under the 25A maximum?

Yes

Problem
The center string is only two panels (2s) and the others are three panels (3s).
This will not perform well. All three strings will output as 2s.

 

[Off Grid/Off My Rocker]

Thanks. I'll add a third panel then to the center string.

 

[timselectric]

A branch connector may not be the best choice.
13.24a x 3 = 39.72a
A 40a branch connector and 40a MC4 connectors are not common.

 

[Off Grid/Off My Rocker]

A branch connector may not be the best choice.
13.24a x 3 = 39.72a
A 40a branch connector and 40a MC4 connectors are not common.

 

[Off Grid/Off My Rocker]

My 3 to 1 branch connectors are rated at 50a, but the MC4 connectors I had in mind are 30a. I'll look for 40a rated MC4 connectors instead. thanks.

 

[Mattb4]

As a heads up. Some of the MC4 inline fuse holders out there are poorly made and cause enough resistance to melt the holder or allow no power through. It is probably best to go to a combiner box if you are running more than 2 strings.

 

[Off Grid/Off My Rocker]

A branch connector may not be the best choice.
13.24a x 3 = 39.72a
A 40a branch connector and 40a MC4 connectors are not common.

Hi There Tim,

So with your advice I have re-configured my setup. 3 Panels in each series, 50a MC4 Branch Connectors, 40a MC4 Connectors and a 20a MC4 Inline Fuse to be placed before the positive branch connector.

Should be good to go?

Thanks again. Much appreciated!
Glenn

 

[timselectric]

Should be good to go?

Good to go.

 

[Off Grid/Off My Rocker]

Good to go.

Hi There Tim,

One final question for if you have a spare moment. In the final set up diagram I sent last Saturday I have three 20A inline fuses connecting to the 3 to 1 MC4 branch connector. Would I also need to fuse the single line coming from the 3 to 1 MC4 branch connector prior to connecting to the inverter as well? I have attached a screen shot of what I am referring to. Although in this example it's a combiner box, it seems to be the same concept as the branch connector set up in my planned array. If it should be fused, what size fuse would suffice? Using the guy's math I'm hoping it's just unnecessary redundancy as I've never seen a 60 amp inline MC4 fuse.

Thanks in advance for your help. Much appreciated.
Glenn

 

[timselectric]

Hi There Tim,

One final question for if you have a spare moment. In the final set up diagram I sent last Saturday I have three 20A inline fuses connecting to the 3 to 1 MC4 branch connector. Would I also need to fuse the single line coming from the 3 to 1 MC4 branch connector prior to connecting to the inverter as well? I have attached a screen shot of what I am referring to. Although in this example it's a combiner box, it seems to be the same concept as the branch connector set up in my planned array. If it should be fused, what size fuse would suffice? Using the guy's math I'm hoping it's just unnecessary redundancy as I've never seen a 60 amp inline MC4 fuse.

Thanks in advance for your help. Much appreciated.
Glenn

No fuse is required after the branch connector. (As long as the conductors are sized correctly)
But, a disconnect near the SCC (or AIO) is recommended for maintenance purposes.
PS: a breaker can be used as a disconnect.
PPS: some AIO's have built in PV disconnects.

 

[Off Grid/Off My Rocker]

No fuse is required after the branch connector. (As long as the conductors are sized correctly)
But, a disconnect near the SCC (or AIO) is recommended for maintenance purposes.
PS: a breaker can be used as a disconnect.
PPS: some AIO's have built in PV disconnects.

Perfect! Thanks again for all your help.