diff --git a/backend/pinscopex/graph.py b/backend/pinscopex/graph.py
index 3b0afa9..3f0da56 100644
--- a/backend/pinscopex/graph.py
+++ b/backend/pinscopex/graph.py
@@ -154,6 +154,11 @@ def _infer_net_properties(name: str) -> tuple[NetType, float | None]:
         voltage = _parse_rail_voltage(name)
         return NetType.POWER, voltage
 
+    # KiCad-style rails: 3V3_DIGITAL, 1V8_SI4684, 5V_USB (not I2C1-SCL-3V3).
+    if re.match(r"^\d+V\d*", upper):
+        voltage = _parse_rail_voltage(name)
+        return NetType.POWER, voltage
+
     # Everything else is a signal
     return NetType.SIGNAL, None
 
diff --git a/backend/pinscopex/passive_rail_check.py b/backend/pinscopex/passive_rail_check.py
index 9a1a2b2..3bbfc95 100644
--- a/backend/pinscopex/passive_rail_check.py
+++ b/backend/pinscopex/passive_rail_check.py
@@ -217,7 +217,23 @@ def _is_i2c_pin(
     pin_num: str,
     net_name: str,
 ) -> bool:
-    return bool(_I2C_RE.search(_pin_blob(cons, pin_num, net_name)))
+    net = net_name or ""
+    if re.match(r"(?i)SPI([_-]|$)", net) or re.search(
+        r"(?i)\bSPI[_-]?(CLK|SCK|MOSI|MISO|CS|SS)\b", net,
+    ):
+        return False
+    primary = ""
+    if cons:
+        pin = cons.pin_by_number(pin_num)
+        if pin and pin.name:
+            primary = pin.name.split("/")[0].strip()
+    if re.search(r"(?i)\b(MISO|MOSI|SCLK|SCK)\b", primary):
+        return False
+    if _I2C_RE.search(net):
+        return True
+    if _I2C_RE.search(primary):
+        return True
+    return False
 
 
 def _is_reset_pin(
@@ -241,7 +257,9 @@ def _is_ground_net(graph: DesignGraph, name: str) -> bool:
 
 def _is_power_net(graph: DesignGraph, name: str) -> bool:
     net = graph.nets.get(name)
-    return bool(net and net.net_type == NetType.POWER)
+    if net and net.net_type == NetType.POWER:
+        return True
+    return bool(re.match(r"^\d+V\d*", (name or "").upper()))
 
 
 def _capacitor_to_ground(graph: DesignGraph, power_net: str) -> bool:
diff --git a/tests/test_passive_rail_check.py b/tests/test_passive_rail_check.py
index 0450256..86afd8e 100644
--- a/tests/test_passive_rail_check.py
+++ b/tests/test_passive_rail_check.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+from backend.pinscopex.graph import _infer_net_properties
 from backend.pinscopex.models import (
     Component,
     ComponentConstraints,
@@ -19,6 +20,17 @@ from backend.pinscopex.passive_rail_check import (
 )
 
 
+def test_ki_cad_voltage_prefix_is_power():
+    ntype, volts = _infer_net_properties("3V3_DIGITAL")
+    assert ntype == NetType.POWER
+    assert volts == 3.3
+    ntype, volts = _infer_net_properties("1V8_SI4684")
+    assert ntype == NetType.POWER
+    assert volts == 1.8
+    ntype, _ = _infer_net_properties("I2C1-SCL-3V3")
+    assert ntype == NetType.SIGNAL
+
+
 def _graph(components, nets):
     net_objs = {}
     for name, (ntype, conns) in nets.items():
@@ -117,6 +129,44 @@ def test_i2c_pullup_present():
     assert check_i2c_pullups(g, cons) == []
 
 
+def test_i2c_pullup_to_3v3_digital_typed_as_signal():
+    cons = {
+        "UTEST": ComponentConstraints(
+            mpn="UTEST",
+            pintable=[Pin(number=8, name="SDA")],
+            absolute_maximum_ratings=[], rules=[],
+        )
+    }
+    r = Component(
+        reference="R1", value="4.7k", footprint="",
+        component_type=ComponentType.RESISTOR, mpn="R1",
+        pins={"1": "I2C_SDA", "2": "3V3_DIGITAL"},
+    )
+    g = _graph(
+        {"U1": _ic("U1", {"8": "I2C_SDA"}), "R1": r},
+        {
+            "I2C_SDA": (NetType.SIGNAL, [("U1", "8"), ("R1", "1")]),
+            "3V3_DIGITAL": (NetType.SIGNAL, [("R1", "2")]),
+        },
+    )
+    assert check_i2c_pullups(g, cons) == []
+
+
+def test_spi_pin_alias_sda_is_not_i2c():
+    cons = {
+        "UTEST": ComponentConstraints(
+            mpn="UTEST",
+            pintable=[Pin(number=38, name="MISO/SDA")],
+            absolute_maximum_ratings=[], rules=[],
+        )
+    }
+    g = _graph(
+        {"U1": _ic("U1", {"38": "SPI_MISO"})},
+        {"SPI_MISO": (NetType.SIGNAL, [("U1", "38")])},
+    )
+    assert check_i2c_pullups(g, cons) == []
+
+
 def test_reset_no_finding_when_gpio_drives():
     cons = {
         "UTEST": ComponentConstraints(