The cable from the MPPT to the battery carries the controller’s full charge current and needs its own fuse at the busbar. Wattonomy computes the gauge and fuse for any controller at 12, 24 or 48 V, to ABYC E-11.
MPPT output current to the battery over a 2.5 m run, sized to ABYC E-11 with a 3% voltage-drop limit.
Cable gauge and fuse from the controller’s battery output, by its rated output current, computed at a 2.5 m run.
| MPPT output | 12 V | 24 V | 48 V |
|---|---|---|---|
| 20 A | 8 AWG20 A · 25 A fuse · 1.9% | 12 AWG20 A · 25 A fuse · 2.5% | 14 AWG20 A · 25 A fuse · 1.9% |
| 30 A | 8 AWG30 A · 40 A fuse · 2.8% | 10 AWG30 A · 40 A fuse · 2.4% | 10 AWG30 A · 40 A fuse · 1.2% |
| 50 A | 6 AWG50 A · 80 A fuse · 2.8% | 6 AWG50 A · 80 A fuse · 1.4% | 6 AWG50 A · 80 A fuse · 0.7% |
| 75 A | 4 AWG75 A · 100 A fuse · 2.7% | 6 AWG75 A · 100 A fuse · 2.1% | 6 AWG75 A · 100 A fuse · 1.1% |
| 100 A | 2 AWG100 A · 125 A fuse · 2.5% | 4 AWG100 A · 125 A fuse · 1.8% | 4 AWG100 A · 125 A fuse · 0.9% |
Figures are the controller’s rated output current over a 2.5 m run, to ABYC E-11 with a 3% voltage-drop limit. The fuse goes at the busbar end of this run — each charge source is protected where it joins the bus. Longer runs need a larger cable; size your exact run in the designer.
The MPPT’s battery cable can carry fault current, so it needs a fuse at the busbar and a conductor sized to carry it. Wattonomy sizes the cable to carry its fuse and hold voltage-drop under 3%, to ABYC E-11.
The controller’s output current and the run length set the gauge; the fuse protects it.
An MPPT outputs up to its rated current (a 100/50 outputs 50 A) regardless of array size — that current sizes the battery cable.
Charge runs are often longer than the inverter feed, so voltage drop matters. The table assumes 2.5 m; the designer takes your real length.
Each charge source is fused where it lands on the busbar, sized to protect the conductor — to ABYC E-11.
Kept under 3% so the battery sees the controller’s full charge voltage.
This table sizes one run. The designer sizes your entire build — battery, inverter, solar, every cable and fuse — and draws the wiring diagram, free.
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It follows the controller’s rated output current and the run length. A 50 A MPPT at 12 V needs about 6 AWG with an 80 A fuse over a short run; at 24 V or 48 V the same controller needs less. Wattonomy sizes it to your exact run.
A fuse at the busbar end, rated to protect the cable while carrying the controller’s output current — for a 50 A controller that’s typically an 80 A fuse on 6 AWG. The designer computes it for your controller.
Often yes for parallel strings, but a single self-limiting string into the MPPT can be exempt (ABYC). The PV-side fuse follows a different rule from the battery-side cable shown here; the designer handles both.
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Plain version: these are the recognized rulebooks your cable and fuse are sized against, so the numbers hold up to a surveyor, an inspector or an insurer.
Wattonomy applies these standards in its calculations. It is not certified, sponsored or endorsed by ABYC, ISO, NFPA or Victron — it sizes your design to meet what they require, and shows the working.
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