diff --git a/engineering/understand/critique.py b/engineering/understand/critique.py
index 10040b5..6cd8c57 100644
--- a/engineering/understand/critique.py
+++ b/engineering/understand/critique.py
@@ -34,12 +34,10 @@ from engineering.layers import PID_LAYERS
 from engineering.pid.lines import PID_LINE_LAYERS
 from engineering.plan_spec import Issue
 from engineering.understand.topology import (
-    NETWORK_CONFIDENCE,
-    NETWORK_DISCIPLINES,
     network_layers,
     topology_findings,
 )
-from engineering.understand.vocab import classify_layer
+from engineering.understand.vocab import is_network_layer
 
 if TYPE_CHECKING:
     from backends.base import AutoCADBackend
@@ -66,13 +64,7 @@ SEMANTIC_LAYERS: frozenset[str] = frozenset(
 
 
 def _is_candidate(name: str) -> bool:
-    if name in SEMANTIC_LAYERS:
-        return False
-    meaning = classify_layer(name)
-    return (
-        meaning.get("discipline") in NETWORK_DISCIPLINES
-        and float(meaning.get("confidence") or 0.0) >= NETWORK_CONFIDENCE
-    )
+    return name not in SEMANTIC_LAYERS and is_network_layer(name)
 
 
 def focus_layers(snap) -> list[str]:
diff --git a/engineering/understand/network.py b/engineering/understand/network.py
index 6529519..ace1d70 100644
--- a/engineering/understand/network.py
+++ b/engineering/understand/network.py
@@ -72,7 +72,7 @@ from dataclasses import dataclass
 
 from engineering.understand.labels import parse_diameters, parse_tag, wiring_target
 from engineering.understand.snapshot import EntityRecord, Pt, Snapshot
-from engineering.understand.vocab import classify_layer, fold, supply_return
+from engineering.understand.vocab import classify_layer, fold, is_network_layer, supply_return
 
 __all__ = [
     "EQUIPMENT_SEARCH_SHARE",
@@ -262,13 +262,10 @@ def _layer_names(snap: Snapshot) -> list[str]:
 
 
 def default_layers(snap: Snapshot) -> tuple[str, ...]:
-    """Every layer `classify_layer` files under piping or electrical with confidence >= 0.9."""
-    chosen = []
-    for name in _layer_names(snap):
-        found = classify_layer(name)
-        if found["discipline"] in NETWORK_DISCIPLINES and found["confidence"] >= NETWORK_CONFIDENCE:
-            chosen.append(name)
-    return tuple(chosen)
+    """Every layer of pipes or cables: `vocab.is_network_layer` - piping or electrical
+    at confidence >= 0.9, and not a layer of valve, pump or tank symbols or of
+    annotation (sizes, materials, numbers), whose lines are no pipe."""
+    return tuple(name for name in _layer_names(snap) if is_network_layer(name))
 
 
 def label_search_default(snap: Snapshot, *, tol: float = 1.0) -> float:
@@ -413,8 +410,9 @@ def _choose_layers(snap: Snapshot, layers) -> tuple[str, ...]:
         chosen = default_layers(snap)
         if not chosen:
             raise ValueError(
-                "layers: no layer is classified piping or electrical with confidence >= 0.9; "
-                f"name the layers to read. The drawing has: {', '.join(known)}"
+                "layers: no layer is classified piping or electrical with confidence >= 0.9 "
+                "(symbol and annotation layers left out); name the layers to read. The drawing "
+                f"has: {', '.join(known)}"
             )
         return chosen
     names = [str(name) for name in layers]
diff --git a/engineering/understand/topology.py b/engineering/understand/topology.py
index ba82994..809265c 100644
--- a/engineering/understand/topology.py
+++ b/engineering/understand/topology.py
@@ -53,7 +53,7 @@ from collections.abc import Iterable
 from dataclasses import dataclass
 
 from engineering.understand.snapshot import EntityRecord, Pt, Snapshot
-from engineering.understand.vocab import classify_layer
+from engineering.understand.vocab import classify_layer, is_network_layer
 
 __all__ = [
     "DEFAULT_TOL",
@@ -219,7 +219,7 @@ def network_layers(snap: Snapshot) -> list[dict]:
     for name in sorted(names):
         meaning = classify_layer(name)
         confidence = float(meaning.get("confidence") or 0.0)
-        if meaning.get("discipline") in NETWORK_DISCIPLINES and confidence >= NETWORK_CONFIDENCE:
+        if is_network_layer(name):
             rows.append(
                 {
                     "layer": name,
diff --git a/engineering/understand/vocab.py b/engineering/understand/vocab.py
index 6803b24..0379baa 100644
--- a/engineering/understand/vocab.py
+++ b/engineering/understand/vocab.py
@@ -32,6 +32,7 @@ __all__ = [
     "classify_layer",
     "equipment_kind",
     "fold",
+    "is_network_layer",
     "room_label",
     "supply_return",
 ]
@@ -438,6 +439,43 @@ def room_label(text: str | None) -> dict | None:
     return None
 
 
+#: Words that make a piping or electrical layer hold annotation, not lines: pipe
+#: sizes, materials, valve or line numbers, hatching. Matched like every other
+#: keyword here (a word of five letters or more anywhere in the name).
+_NOT_A_LINE_WORDS = (
+    ("annotation", "diameter", "en"),
+    ("annotation", "sizes", "en"),
+    ("annotation", "size", "en"),
+    ("annotation", "material", "en"),
+    ("annotation", "number", "en"),
+    ("annotation", "nummer", "nl"),
+    ("annotation", "arcering", "nl"),
+    ("annotation", "hatch", "en"),
+)
+
+
+def is_network_layer(name: str | None) -> bool:
+    """A layer whose lines are pipes or cables.
+
+    `classify_layer` files it under piping or electrical at 0.9, and its name
+    says neither that it holds symbols - a valve, pump, tank, motor, panel or
+    reducer (`equipment_kind`), whose outlines are no pipe - nor that it holds
+    annotation: sizes, materials, numbers, hatching, or an annotation word.
+    Field P&IDs keep valves and pumps on their own layers (``KLEPPEN``,
+    ``PRODUCT PUMPS``) that a service keyword alone would read as piping.
+    """
+    meaning = classify_layer(name)
+    if meaning["discipline"] not in ("piping", "electrical") or meaning["confidence"] < DIRECT:
+        return False
+    if equipment_kind(name) is not None:
+        return False
+    folded = fold(name)
+    if _first(_NOT_A_LINE_WORDS, folded) is not None:
+        return False
+    annotation = [row for row in _DISCIPLINE_WORDS if row[0] == "annotation"]
+    return _first(annotation, folded) is None
+
+
 def equipment_kind(block_name: str | None) -> dict | None:
     """The kind of equipment a block name says it is: ``{"kind", "keyword", "language"}``.
 
diff --git a/tests/test_understand_vocab.py b/tests/test_understand_vocab.py
index cd4a058..ffb939d 100644
--- a/tests/test_understand_vocab.py
+++ b/tests/test_understand_vocab.py
@@ -17,6 +17,7 @@ from engineering.understand.vocab import (
     classify_layer,
     equipment_kind,
     fold,
+    is_network_layer,
     room_label,
     supply_return,
 )
@@ -232,3 +233,31 @@ def test_block_names_say_their_kind(block, kind, language):
 def test_an_anonymous_block_has_no_kind():
     assert equipment_kind("*U12") is None
     assert equipment_kind(None) is None
+
+
+@pytest.mark.parametrize(
+    ("name", "network"),
+    [
+        ("P_product piping", True),
+        ("P_cipsupplyline", True),
+        ("E_power", True),
+        # symbols, not lines: the layer names the equipment drawn on it
+        ("KLEPPEN", False),
+        ("Valve_ball valves", False),
+        ("PRODUCT PUMPS", False),
+        ("CIP return pumps", False),
+        ("Storage tanks", False),
+        ("E_panel connections", False),
+        # annotation on a piping layer: sizes, materials, numbers, hatching
+        ("P_pipe diameters", False),
+        ("PIPESIZES", False),
+        ("piping materials", False),
+        ("valve numbers", False),
+        ("PIPE TEXT", False),
+        # not piping or electrical at all
+        ("WALLS", False),
+        ("0", False),
+    ],
+)
+def test_a_network_layer_holds_lines_not_symbols_or_annotation(name, network):
+    assert is_network_layer(name) is network