What is Maximum Series Fuse?
You will find the 'maximum series fuse' rating on each solar panel spec sheet and/or panel nameplate (the sticker on the back of your solar panel). As you can see from the two examples below the Maximum Series Fuse is 15A for both the Maxeon 470W and SunPower 100W panels.
Sounds interesting right, how can a big 470W fixed frame panel and a much smaller 100W flex panel have the same rating? Keep reading to learn why...
What is this rating telling us?
The maximum series fuse rating of 15A is telling us that a maximum of 15A should be able to flow through this solar panel when multiple panels (or strings of panels in series) are wired together in parallel. As such a 15A fuse is the largest (highest) that should be used in-line to protect the panel and will blow when a current greater than ~15A tries to pass.
Remember when solar panels are wired together in parallel the voltage stays the same but current (amps) increases
Examples of multiple SunPower 100W flex panels wired together in parallel:
2x100W panels wired in parallel - current increases to 12.4A (no in-line fuse required)
3x100W panels wired in parallel - current increases to 18.6A (in-line 15A fuse required)
4x100W panels wired in parallel - current increases to 24.8A (in-line 15A fuse required)
As you can see above with 2x100W panels wired in parallel the total current remains below 15A so no in-line fuse required.
With 3x100W panels wired in parallel the total current is 18.6A so a 15A in-line MC4 fuse is required. It's worth saying this would be unusual but it can happen, for some reason there is a 'bad panel' and the other 'good' panels try to back feed current (amps) into it. You could have the combined 2x100W 'good' panels plus whatever the 'bad' panel might still be producing and you may exceed the maximum series fuse rating of 15A. A hot spot could occur, panel heats up and there is a risk of panel melting/fire....not good.
To prevent this from happening some over current protection can be installed, in this example below you would need 3x 15A in-line MC4 fuses, installed on the positive wire from each 100W panel.
3x100W panels wired in parallel with in-line MC4 fuses (15A)
In-line MC4 fuses are easy to install and simply click together with the male and female MC4 connectors on either end. The fuses are easily replaceable by unscrewing either end so it's worth having some spares aboard!
User replaceable fuse inside
Here's a table of Maximum Series Fuse ratings for the Maxeon & SunPower solar panels we have in stock:
Solar panel | Max Series Fuse | Panel Isc | Fuse required for |
50W flex | 15A | 3.1A | 5 panels in parallel |
100W flex | 15A | 6.3A | 3 panels in parallel |
330W flex | 20A | 6.28A | 4 panels in parallel |
415W-R fixed | 25A | 12.64A | 2 panels in parallel |
470W fixed | 15A | 6.45A | 3 panels in parallel |
475W fixed | 20A | 11.57A | 2 panels in parallel |
Summary
Over current protection (OCP) with in-line MC4 fuses is only a consideration if your panels are wired in parallel (not series)
Check the Maximum Series Rating for your solar panel by looking at the panel spec sheet or sticker on the back of the panel
If required install 1x in-line MC4 fuse (appropriately sixed) on the positive wire of each panel in the string.
Should you have any questions please don't hesitate to get in touch with us.
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