diff --git a/src/zepben/evolve/model/cim/iec61970/base/core/equipment.py b/src/zepben/evolve/model/cim/iec61970/base/core/equipment.py
index 6e3e436b8..dcb99d570 100644
--- a/src/zepben/evolve/model/cim/iec61970/base/core/equipment.py
+++ b/src/zepben/evolve/model/cim/iec61970/base/core/equipment.py
@@ -1,4 +1,4 @@
-#  Copyright 2024 Zeppelin Bend Pty Ltd
+#  Copyright 2025 Zeppelin Bend Pty Ltd
 #  This Source Code Form is subject to the terms of the Mozilla Public
 #  License, v. 2.0. If a copy of the MPL was not distributed with this
 #  file, You can obtain one at https://mozilla.org/MPL/2.0/.
@@ -132,19 +132,19 @@ def num_substations(self) -> int:
         """
         Returns The number of `zepben.evolve.cim.iec61970.base.core.substation.Substation`s associated with this `Equipment`
         """
-        return len(_of_type(self._equipment_containers, Substation))
+        return len(list(_of_type(self._equipment_containers, Substation)))
 
     def num_sites(self) -> int:
         """
         Returns The number of `Site`s associated with this `Equipment`
         """
-        return len(_of_type(self._equipment_containers, Site))
+        return len(list(_of_type(self._equipment_containers, Site)))
 
     def num_normal_feeders(self) -> int:
         """
         Returns The number of normal `Feeder`s associated with this `Equipment`
         """
-        return len(_of_type(self._equipment_containers, Feeder))
+        return len(list(_of_type(self._equipment_containers, Feeder)))
 
     def num_usage_points(self) -> int:
         """
@@ -358,9 +358,6 @@ def clear_operational_restrictions(self) -> Equipment:
         return self
 
 
-def _of_type(containers: Optional[List[EquipmentContainer]], ectype: Type[TEquipmentContainer]) -> List[TEquipmentContainer]:
-    if containers:
-        return [ec for ec in containers if isinstance(ec, ectype)]
-    else:
-        return []
+def _of_type(containers: Optional[List[EquipmentContainer]], ectype: Type[TEquipmentContainer]) -> Generator[TEquipmentContainer, None, None]:
+    yield from (ec for ec in containers if isinstance(ec, ectype)) if containers is not None else {}
 
diff --git a/src/zepben/evolve/model/cim/iec61970/base/wires/per_length_phase_impedance.py b/src/zepben/evolve/model/cim/iec61970/base/wires/per_length_phase_impedance.py
index 20fc308a5..f9f4460f9 100644
--- a/src/zepben/evolve/model/cim/iec61970/base/wires/per_length_phase_impedance.py
+++ b/src/zepben/evolve/model/cim/iec61970/base/wires/per_length_phase_impedance.py
@@ -1,4 +1,4 @@
-#  Copyright 2024 Zeppelin Bend Pty Ltd
+#  Copyright 2025 Zeppelin Bend Pty Ltd
 #  This Source Code Form is subject to the terms of the Mozilla Public
 #  License, v. 2.0. If a copy of the MPL was not distributed with this
 #  file, You can obtain one at https://mozilla.org/MPL/2.0/.
@@ -41,7 +41,7 @@ def diagonal(self) -> Generator[PhaseImpedanceData, None, None]:
         """
         Get only the diagonal elements of the matrix, i.e toPhase == fromPhase.
         """
-        return ngen([pid for pid in self._data if pid.from_phase == pid.to_phase])
+        return ngen(pid for pid in self._data if pid.from_phase == pid.to_phase)
 
     def num_data(self):
         """Return the number of :class:`PhaseImpedanceData` associated with this :class:`PerLengthPhaseImpedance`."""
diff --git a/src/zepben/evolve/util.py b/src/zepben/evolve/util.py
index 0d958d62a..a9109ba81 100644
--- a/src/zepben/evolve/util.py
+++ b/src/zepben/evolve/util.py
@@ -111,9 +111,7 @@ def nlen(sized: Optional[Sized]) -> int:
 
 
 def ngen(collection: Optional[Iterable[T]]) -> Generator[T, None, None]:
-    if collection:
-        for item in collection:
-            yield item
+    yield from collection or {}
 
 
 def is_none_or_empty(sized: Optional[Sized]) -> bool: