diff --git a/docs/circuit-list-editor-interactions.md b/docs/circuit-list-editor-interactions.md
index 8b799db..7b1aabc 100644
--- a/docs/circuit-list-editor-interactions.md
+++ b/docs/circuit-list-editor-interactions.md
@@ -37,6 +37,9 @@ Selection, keyboard movement, and editability checks run against this normalized
 - `Tab` / `Shift+Tab`: move between editable cells (commits active edit)
 - arrow keys: move selected cell in grid when not editing
 - type-to-edit: printable keys open edit mode and replace current display value with typed character
+- `Ctrl+Plus` / `Ctrl+Shift+Plus`: insert below the selected circuit or device context
+
+For insertion, a circuit-level cell creates a reserve circuit directly after the selected circuit. A device-level cell creates a manual device row directly after the selected device. On the virtual `-frei-` row, or without a valid row selection, the shortcut creates a circuit at the end of the active section. Insertions use command history and never renumber existing equipment identifiers.
 
 ## `-frei-` Placeholder Behavior
 
diff --git a/package.json b/package.json
index 0fa23fd..da706fa 100644
--- a/package.json
+++ b/package.json
@@ -11,8 +11,8 @@
     "build:api": "tsc -p tsconfig.json",
     "build:web": "next build",
     "start": "node dist/server/index.js",
-    "test": "tsx --test tests/power-calculation.test.ts tests/consumer-linking.service.test.ts tests/consumer-schema-options.test.ts tests/project-device-schema.test.ts tests/project-device-placement.service.test.ts tests/project-device-sync.service.test.ts tests/legacy-consumer-migration-planner.test.ts tests/circuit-numbering.service.test.ts tests/circuit-write.rules.test.ts tests/circuit-power-calculation.test.ts tests/circuit-tree.controller.test.ts",
-    "test:watch": "tsx --watch --test tests/power-calculation.test.ts tests/consumer-linking.service.test.ts tests/consumer-schema-options.test.ts tests/project-device-schema.test.ts tests/project-device-placement.service.test.ts tests/project-device-sync.service.test.ts tests/legacy-consumer-migration-planner.test.ts tests/circuit-numbering.service.test.ts tests/circuit-write.rules.test.ts tests/circuit-power-calculation.test.ts tests/circuit-tree.controller.test.ts",
+    "test": "tsx --test tests/power-calculation.test.ts tests/consumer-linking.service.test.ts tests/consumer-schema-options.test.ts tests/project-device-schema.test.ts tests/project-device-placement.service.test.ts tests/project-device-sync.service.test.ts tests/legacy-consumer-migration-planner.test.ts tests/circuit-numbering.service.test.ts tests/circuit-write.rules.test.ts tests/circuit-power-calculation.test.ts tests/circuit-tree.controller.test.ts tests/circuit-grid-insertion.test.ts",
+    "test:watch": "tsx --watch --test tests/power-calculation.test.ts tests/consumer-linking.service.test.ts tests/consumer-schema-options.test.ts tests/project-device-schema.test.ts tests/project-device-placement.service.test.ts tests/project-device-sync.service.test.ts tests/legacy-consumer-migration-planner.test.ts tests/circuit-numbering.service.test.ts tests/circuit-write.rules.test.ts tests/circuit-power-calculation.test.ts tests/circuit-tree.controller.test.ts tests/circuit-grid-insertion.test.ts",
     "db:generate": "drizzle-kit generate",
     "db:migrate": "drizzle-kit migrate",
     "db:backup": "node scripts/db-backup.js",
diff --git a/src/frontend/components/circuit-tree-editor.tsx b/src/frontend/components/circuit-tree-editor.tsx
index 6f23b6b..9b27eda 100644
--- a/src/frontend/components/circuit-tree-editor.tsx
+++ b/src/frontend/components/circuit-tree-editor.tsx
@@ -5,6 +5,10 @@ import {
   inferProjectDeviceSectionKey,
   isProjectDevicePlacementValid,
 } from "../../domain/services/project-device-placement.service";
+import {
+  getInsertionSortOrder,
+  resolveGridInsertionIntent,
+} from "../utils/circuit-grid-insertion";
 import {
   createCircuit,
   createCircuitDeviceRow,
@@ -1616,7 +1620,7 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
     requestAnimationFrame(() => containerRef.current?.focus());
   }
 
-  async function handleAddReserveCircuit(sectionId: string) {
+  async function handleAddReserveCircuit(sectionId: string, afterCircuitId?: string) {
     const section = data?.sections.find((entry) => entry.id === sectionId);
     if (!section) {
       return;
@@ -1626,8 +1630,7 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
       label: "Add circuit",
       redo: async () => {
         const next = await getNextCircuitIdentifier(sectionId);
-        const sortOrder =
-          section.circuits.length > 0 ? Math.max(...section.circuits.map((circuit) => circuit.sortOrder)) + 10 : 10;
+        const sortOrder = getInsertionSortOrder(section.circuits, afterCircuitId);
         const created = (await createCircuit(projectId, circuitListId, {
           sectionId,
           equipmentIdentifier: next.nextIdentifier,
@@ -1659,7 +1662,13 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
     });
   }
 
-  async function handleAddManualDevice(circuit: CircuitTreeCircuitDto, sectionId: string) {
+  async function handleAddManualDevice(
+    circuit: CircuitTreeCircuitDto,
+    sectionId: string,
+    afterDeviceRowId?: string
+  ) {
+    const originalDeviceCount = circuit.deviceRows.length;
+    const section = data?.sections.find((entry) => entry.id === sectionId);
     let createdRowId: string | null = null;
     await runCommand({
       label: "Add manual device",
@@ -1667,18 +1676,19 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
         const created = (await createCircuitDeviceRow(circuit.id, {
           name: "Manual device",
           displayName: "Manual device",
-          phaseType: "single_phase",
+          phaseType: section?.key === "three_phase" ? "three_phase" : "single_phase",
           quantity: 1,
           powerPerUnit: 0,
           simultaneityFactor: 1,
           cosPhi: 1,
+          sortOrder: getInsertionSortOrder(circuit.deviceRows, afterDeviceRowId),
         })) as { id: string };
         createdRowId = created.id;
         setActiveSectionId(sectionId);
         return {
-          rowKey: `device:${created.id}`,
+          rowKey: originalDeviceCount === 0 ? `circuitCompact:${circuit.id}` : `device:${created.id}`,
           cellKey: "displayName",
-          rowType: "deviceRow",
+          rowType: originalDeviceCount === 0 ? "circuitCompact" : "deviceRow",
           sectionId,
           circuitId: circuit.id,
           deviceId: created.id,
@@ -1688,17 +1698,68 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
         if (createdRowId) {
           await deleteCircuitDeviceRowById(createdRowId);
         }
+        const rowKey =
+          originalDeviceCount === 0
+            ? `reserveCircuit:${circuit.id}`
+            : originalDeviceCount === 1
+              ? `circuitCompact:${circuit.id}`
+              : afterDeviceRowId
+                ? `device:${afterDeviceRowId}`
+                : `circuitSummary:${circuit.id}`;
         return {
-          rowKey: `reserveCircuit:${circuit.id}`,
+          rowKey,
           cellKey: "displayName",
-          rowType: "reserveCircuit",
+          rowType:
+            originalDeviceCount === 0
+              ? "reserveCircuit"
+              : originalDeviceCount === 1
+                ? "circuitCompact"
+                : afterDeviceRowId
+                  ? "deviceRow"
+                  : "circuitSummary",
           sectionId,
           circuitId: circuit.id,
+          deviceId: afterDeviceRowId,
         };
       },
     });
   }
 
+  async function handleInsertBelowSelection() {
+    const row = selectedCell ? findRow(selectedCell.rowKey) : null;
+    const cell = row?.cells.find((entry) => entry.cellKey === selectedCell?.cellKey);
+    const selection =
+      row && cell && row.rowType !== "section"
+        ? {
+            rowType: row.rowType,
+            cellKind: cell.kind,
+            sectionId: row.sectionId,
+            circuitId: row.circuit?.id,
+            deviceId: row.device?.id,
+          }
+        : null;
+    const intent = resolveGridInsertionIntent(
+      selection,
+      activeSectionId ?? data?.sections[0]?.id
+    );
+    if (!intent) {
+      setError("No section is available for insertion.");
+      return;
+    }
+    if (intent.kind === "circuit") {
+      await handleAddReserveCircuit(intent.sectionId, intent.afterCircuitId);
+      return;
+    }
+    const circuit = data?.sections
+      .flatMap((sectionEntry) => sectionEntry.circuits)
+      .find((entry) => entry.id === intent.circuitId);
+    if (!circuit) {
+      setError("Invalid circuit id.");
+      return;
+    }
+    await handleAddManualDevice(circuit, intent.sectionId, intent.afterDeviceRowId);
+  }
+
   function resolvePhaseType(device: ProjectDeviceDto): string {
     return device.phaseType;
   }
@@ -2472,10 +2533,7 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
       (event.key === "+" || (event.shiftKey && event.key === "=") || event.code === "NumpadAdd");
     if (isCtrlPlus) {
       event.preventDefault();
-      const sectionId = activeSectionId ?? data?.sections[0]?.id;
-      if (sectionId) {
-        void handleAddReserveCircuit(sectionId);
-      }
+      void handleInsertBelowSelection();
       return;
     }
     if (event.key === "Tab" && selectedCell) {
@@ -3486,7 +3544,9 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
           </table>
         </div>
       </div>
-      <p className="todo-hint">TODO Phase: Ctrl+Plus currently adds circuit at end of active section.</p>
+      <p className="todo-hint">
+        Ctrl+Plus inserts below the selected circuit or device context. Use Undo to revert the insertion.
+      </p>
     </div>
   );
 }
diff --git a/src/frontend/utils/circuit-grid-insertion.ts b/src/frontend/utils/circuit-grid-insertion.ts
new file mode 100644
index 0000000..ccb73ad
--- /dev/null
+++ b/src/frontend/utils/circuit-grid-insertion.ts
@@ -0,0 +1,79 @@
+export type GridInsertionRowType =
+  | "circuitCompact"
+  | "circuitSummary"
+  | "deviceRow"
+  | "reserveCircuit"
+  | "placeholder";
+
+export type GridInsertionCellKind = "circuitField" | "deviceField" | "readonly" | "computed";
+
+export interface GridInsertionSelection {
+  rowType: GridInsertionRowType;
+  cellKind: GridInsertionCellKind;
+  sectionId: string;
+  circuitId?: string;
+  deviceId?: string;
+}
+
+export type GridInsertionIntent =
+  | { kind: "circuit"; sectionId: string; afterCircuitId?: string }
+  | { kind: "device"; sectionId: string; circuitId: string; afterDeviceRowId?: string };
+
+export function resolveGridInsertionIntent(
+  selection: GridInsertionSelection | null,
+  fallbackSectionId?: string
+): GridInsertionIntent | null {
+  if (!selection) {
+    return fallbackSectionId ? { kind: "circuit", sectionId: fallbackSectionId } : null;
+  }
+
+  if (selection.rowType === "placeholder") {
+    return { kind: "circuit", sectionId: selection.sectionId };
+  }
+
+  const targetsDevice =
+    selection.rowType === "deviceRow" ||
+    ((selection.rowType === "circuitCompact" || selection.rowType === "reserveCircuit") &&
+      selection.cellKind === "deviceField");
+
+  if (targetsDevice && selection.circuitId) {
+    return {
+      kind: "device",
+      sectionId: selection.sectionId,
+      circuitId: selection.circuitId,
+      afterDeviceRowId: selection.deviceId,
+    };
+  }
+
+  if (selection.circuitId) {
+    return {
+      kind: "circuit",
+      sectionId: selection.sectionId,
+      afterCircuitId: selection.circuitId,
+    };
+  }
+
+  return { kind: "circuit", sectionId: selection.sectionId };
+}
+
+export function getInsertionSortOrder(
+  orderedEntries: Array<{ id: string; sortOrder: number }>,
+  afterId?: string
+): number {
+  if (orderedEntries.length === 0) {
+    return 10;
+  }
+  if (!afterId) {
+    return Math.max(...orderedEntries.map((entry) => entry.sortOrder)) + 10;
+  }
+
+  const entries = [...orderedEntries].sort((left, right) => left.sortOrder - right.sortOrder);
+  const index = entries.findIndex((entry) => entry.id === afterId);
+  if (index < 0) {
+    return entries[entries.length - 1].sortOrder + 10;
+  }
+
+  const current = entries[index].sortOrder;
+  const next = entries[index + 1]?.sortOrder;
+  return next === undefined ? current + 10 : current + (next - current) / 2;
+}
diff --git a/tests/circuit-grid-insertion.test.ts b/tests/circuit-grid-insertion.test.ts
new file mode 100644
index 0000000..d4cf108
--- /dev/null
+++ b/tests/circuit-grid-insertion.test.ts
@@ -0,0 +1,85 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import {
+  getInsertionSortOrder,
+  resolveGridInsertionIntent,
+} from "../src/frontend/utils/circuit-grid-insertion.js";
+
+describe("circuit grid insertion", () => {
+  it("inserts a circuit after circuit-level selections", () => {
+    assert.deepEqual(
+      resolveGridInsertionIntent(
+        {
+          rowType: "circuitCompact",
+          cellKind: "circuitField",
+          sectionId: "section-1",
+          circuitId: "circuit-1",
+          deviceId: "row-1",
+        },
+        "fallback"
+      ),
+      { kind: "circuit", sectionId: "section-1", afterCircuitId: "circuit-1" }
+    );
+  });
+
+  it("inserts a device after device-level selections in compact and expanded circuits", () => {
+    assert.deepEqual(
+      resolveGridInsertionIntent({
+        rowType: "circuitCompact",
+        cellKind: "deviceField",
+        sectionId: "section-1",
+        circuitId: "circuit-1",
+        deviceId: "row-1",
+      }),
+      {
+        kind: "device",
+        sectionId: "section-1",
+        circuitId: "circuit-1",
+        afterDeviceRowId: "row-1",
+      }
+    );
+    assert.deepEqual(
+      resolveGridInsertionIntent({
+        rowType: "deviceRow",
+        cellKind: "deviceField",
+        sectionId: "section-1",
+        circuitId: "circuit-1",
+        deviceId: "row-2",
+      }),
+      {
+        kind: "device",
+        sectionId: "section-1",
+        circuitId: "circuit-1",
+        afterDeviceRowId: "row-2",
+      }
+    );
+  });
+
+  it("uses the active section for placeholders and missing selections", () => {
+    assert.deepEqual(
+      resolveGridInsertionIntent({
+        rowType: "placeholder",
+        cellKind: "deviceField",
+        sectionId: "section-1",
+      }),
+      { kind: "circuit", sectionId: "section-1" }
+    );
+    assert.deepEqual(resolveGridInsertionIntent(null, "section-2"), {
+      kind: "circuit",
+      sectionId: "section-2",
+    });
+  });
+
+  it("creates stable sort values between neighbours or at the end", () => {
+    const entries = [
+      { id: "a", sortOrder: 10 },
+      { id: "b", sortOrder: 20 },
+      { id: "c", sortOrder: 30 },
+    ];
+
+    assert.equal(getInsertionSortOrder(entries, "a"), 15);
+    assert.equal(getInsertionSortOrder(entries, "c"), 40);
+    assert.equal(getInsertionSortOrder(entries), 40);
+    assert.equal(getInsertionSortOrder([], "missing"), 10);
+  });
+});