Got error R749? Here's how to fix it.
You're seeing this error because the numbers in your project don't pass the 120% rule — a code requirement that limits how much backfed current a busbar can handle.
The good news: it's usually a quick fix. Follow the steps below to find the issue and resubmit.
Potential Solution(s):
Step 1: Confirm you're using the right compliance method
Before changing any numbers, make sure the 120% rule is actually the right compliance method for your busbar. It's common for installers to select it by default when a different method applies.
Go to Electrical Section → Busbars and check the compliance method selected for each busbar showing the error.
Other valid options include:
- 100% rule — NEC 705.12(B)(1)
- Sum of breakers rule — NEC 705.12(B)(3)
- Power control system (PCS) — NEC 705.13
- Supply-side tap — NEC 705.12(A) (not subject to the 120% rule at all)
If a different method better matches your design, switch it and resubmit before going further.
Not sure if your numbers pass? Use the calculator below.
Step 2: Check your input values
If the 120% rule is correct for your design, the issue is likely a wrong value entered in SolarAPP+. Verify these three things match your plan set:
| What to check | Where in SolarAPP+ |
|---|---|
| Busbar rating (Amps) | Electrical → Busbars |
| OCPD protecting the busbar (Amps) | Electrical → Busbars |
| Inverter OCPD rating (Amps) | Electrical → Equipment & Circuit Requirements |
| ESS OCPD rating (Amps) | Electrical → Equipment & Circuit Requirements |
This error can be triggered by any busbar in your project, not just the main service panel — check subpanels too.
Step 3: Fix the values and resubmit
Once you've identified the mismatch, try one of these fixes:
- Reduce the PV or ESS OCPD size
- Derate the main breaker (e.g. 200A → 175A)
- Correct the busbar rating if it was entered wrong
When you're ready, click Review to resubmit.
Step 4: Still stuck?
If you've worked through the steps above and the error is still there, our SolarAPP+ Assist team can look at your project directly.