diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagPath.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagPath.cs
new file mode 100644
index 00000000..69414ab7
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagPath.cs
@@ -0,0 +1,13 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+/// <summary>
+///     Normalizes a parsed CIP route for libplctag's <c>Path</c> attribute. libplctag rejects an
+///     empty-string path with <c>ErrorBadData</c>; "no route" (Micro800, unrouted MicroLogix) must be
+///     expressed by omitting the attribute, i.e. <see langword="null"/>.
+/// </summary>
+internal static class LibplctagPath
+{
+    /// <summary>Returns <see langword="null"/> for a null, empty or whitespace path; otherwise the path unchanged.</summary>
+    /// <param name="path">The parsed CIP path.</param>
+    public static string? Normalize(string? path) => string.IsNullOrWhiteSpace(path) ? null : path;
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagEnumerator.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagEnumerator.cs
index 304baae7..486dcbfc 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagEnumerator.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagEnumerator.cs
@@ -37,7 +37,7 @@ internal static class LibplctagListingReader
     internal static Tag BuildSymbolListTag(AbCipTagCreateParams deviceParams, string listingName = "@tags") => new()
     {
         Gateway = deviceParams.LibplctagGateway,
-        Path = deviceParams.CipPath,
+        Path = LibplctagPath.Normalize(deviceParams.CipPath),
         PlcType = MapPlcType(deviceParams.LibplctagPlcAttribute),
         Protocol = Protocol.ab_eip,
         Name = listingName,
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagRuntime.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagRuntime.cs
index f0655678..cfe3761c 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagRuntime.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagRuntime.cs
@@ -18,12 +18,18 @@ internal sealed class LibplctagTagRuntime : IAbCipTagRuntime
     /// <param name="p">The tag creation parameters.</param>
     public LibplctagTagRuntime(AbCipTagCreateParams p)
     {
-        _tag = new Tag
+        _tag = BuildTag(p);
+    }
+
+    /// <summary>Builds the (uninitialized) libplctag tag for <paramref name="p"/>.</summary>
+    /// <param name="p">The tag creation parameters.</param>
+    internal static Tag BuildTag(AbCipTagCreateParams p) =>
+        new Tag
         {
             // host:port — see AbLegacyTagCreateParams/AbCipTagCreateParams.LibplctagGateway.
             // Passing p.Gateway alone drops the authored port onto libplctag's 44818 default (#534).
             Gateway = p.LibplctagGateway,
-            Path = p.CipPath,
+            Path = LibplctagPath.Normalize(p.CipPath),
             PlcType = MapPlcType(p.LibplctagPlcAttribute),
             Protocol = Protocol.ab_eip,
             Name = p.TagName,
@@ -33,7 +39,6 @@ internal sealed class LibplctagTagRuntime : IAbCipTagRuntime
             // count so libplctag pulls every element in one CIP read; scalar tags pass 1.
             ElementCount = p.ElementCount > 1 ? p.ElementCount : 1,
         };
-    }
 
     /// <inheritdoc />
     public Task InitializeAsync(CancellationToken cancellationToken) =>
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTemplateReader.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTemplateReader.cs
index 2fc4d94f..e04864d6 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTemplateReader.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTemplateReader.cs
@@ -39,7 +39,7 @@ internal sealed class LibplctagTemplateReader : IAbCipTemplateReader
     internal static Tag BuildTemplateTag(AbCipTagCreateParams deviceParams, uint templateInstanceId) => new()
     {
         Gateway = deviceParams.LibplctagGateway,
-        Path = deviceParams.CipPath,
+        Path = LibplctagPath.Normalize(deviceParams.CipPath),
         PlcType = MapPlcType(deviceParams.LibplctagPlcAttribute),
         Protocol = Protocol.ab_eip,
         Name = $"@udt/{templateInstanceId}",
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs
index c15605f6..5cb03a08 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs
@@ -17,19 +17,24 @@ internal sealed class LibplctagLegacyTagRuntime : IAbLegacyTagRuntime
     /// <param name="p">The parameters for tag creation.</param>
     public LibplctagLegacyTagRuntime(AbLegacyTagCreateParams p)
     {
-        _tag = new Tag
+        _tag = BuildTag(p);
+    }
+
+    /// <summary>Builds the (uninitialized) libplctag tag for <paramref name="p"/>.</summary>
+    /// <param name="p">The tag creation parameters.</param>
+    internal static Tag BuildTag(AbLegacyTagCreateParams p) =>
+        new Tag
         {
             // host:port — see AbLegacyTagCreateParams/AbCipTagCreateParams.LibplctagGateway.
             // Passing p.Gateway alone drops the authored port onto libplctag's 44818 default (#534).
             Gateway = p.LibplctagGateway,
-            Path = p.CipPath,
+            Path = LibplctagPath.Normalize(p.CipPath),
             PlcType = MapPlcType(p.LibplctagPlcAttribute),
             Protocol = Protocol.ab_eip, // PCCC-over-EIP; libplctag routes via the PlcType-specific PCCC layer
             Name = p.TagName,
             Timeout = p.Timeout,
             ElementCount = p.ElementCount > 1 ? p.ElementCount : null,
         };
-    }
 
     /// <inheritdoc />
     public Task InitializeAsync(CancellationToken cancellationToken) =>
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagPath.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagPath.cs
new file mode 100644
index 00000000..a7104292
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagPath.cs
@@ -0,0 +1,13 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+
+/// <summary>
+///     Normalizes a parsed CIP route for libplctag's <c>Path</c> attribute. libplctag rejects an
+///     empty-string path with <c>ErrorBadData</c>; "no route" (Micro800, unrouted MicroLogix) must be
+///     expressed by omitting the attribute, i.e. <see langword="null"/>.
+/// </summary>
+internal static class LibplctagPath
+{
+    /// <summary>Returns <see langword="null"/> for a null, empty or whitespace path; otherwise the path unchanged.</summary>
+    /// <param name="path">The parsed CIP path.</param>
+    public static string? Normalize(string? path) => string.IsNullOrWhiteSpace(path) ? null : path;
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbCipReadSmokeTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbCipReadSmokeTests.cs
index 44d142e7..a6a5c1cd 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbCipReadSmokeTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbCipReadSmokeTests.cs
@@ -32,7 +32,9 @@ public sealed class AbCipReadSmokeTests
             // smoke test was missed.
             // Micro800 has no backplane: its cip-path is empty (the compose service runs
             // ab_server --plc=Micro800 with no --path, which refuses a routed request). Every
-            // other family reaches slot 0 through `1,0`.
+            // other family reaches slot 0 through `1,0`. Both transports are expected to pass
+            // for Micro800: the libplctag adapters map the empty route to a null `path` attribute
+            // (LibplctagPath.Normalize) because libplctag rejects "" with ErrorBadData.
             var cipPath = profile.Family == AbCipPlcFamily.Micro800 ? "" : "1,0";
             var deviceUri = $"ab://{fixture.Host}:{fixture.Port}/{cipPath}";
             var drv = new AbCipDriver(new AbCipDriverOptions
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/LibplctagEmptyPathTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/LibplctagEmptyPathTests.cs
new file mode 100644
index 00000000..4cd93ba5
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/LibplctagEmptyPathTests.cs
@@ -0,0 +1,51 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+/// <summary>
+///     libplctag rejects an empty-string <c>path</c> with <c>ErrorBadData</c>; "no route" (Micro800, or any
+///     unrouted device authored as <c>ab://host:44818/</c>) must reach it as null. Pre-dates the native transport.
+/// </summary>
+public sealed class LibplctagEmptyPathTests
+{
+    private static AbCipTagCreateParams Params(string cipPath) =>
+        new(Gateway: "10.100.0.35", Port: 44818, CipPath: cipPath, LibplctagPlcAttribute: "micro800",
+            TagName: "TestDINT", Timeout: TimeSpan.FromSeconds(5));
+
+    [Theory]
+    [InlineData("", null)]
+    [InlineData("   ", null)]
+    [InlineData(null, null)]
+    [InlineData("1,0", "1,0")]
+    public void Normalize_maps_blank_to_null_and_keeps_a_route(string? input, string? expected) =>
+        LibplctagPath.Normalize(input).ShouldBe(expected);
+
+    [Fact]
+    public void The_data_tag_omits_the_path_for_an_empty_route()
+    {
+        using var tag = LibplctagTagRuntime.BuildTag(Params(""));
+        tag.Path.ShouldBeNull();
+    }
+
+    [Fact]
+    public void The_data_tag_keeps_a_real_route()
+    {
+        using var tag = LibplctagTagRuntime.BuildTag(Params("1,0"));
+        tag.Path.ShouldBe("1,0");
+    }
+
+    [Fact]
+    public void The_symbol_list_tag_omits_the_path_for_an_empty_route()
+    {
+        using var tag = LibplctagListingReader.BuildSymbolListTag(Params(""));
+        tag.Path.ShouldBeNull();
+    }
+
+    [Fact]
+    public void The_template_tag_omits_the_path_for_an_empty_route()
+    {
+        using var tag = LibplctagTemplateReader.BuildTemplateTag(Params(""), templateInstanceId: 1);
+        tag.Path.ShouldBeNull();
+    }
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/LibplctagEmptyPathTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/LibplctagEmptyPathTests.cs
new file mode 100644
index 00000000..9871bfa4
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/LibplctagEmptyPathTests.cs
@@ -0,0 +1,37 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
+
+/// <summary>
+///     libplctag rejects an empty-string <c>path</c> with <c>ErrorBadData</c>; an unrouted MicroLogix
+///     (<c>ab://host:44818/</c>) must reach it as null.
+/// </summary>
+public sealed class LibplctagEmptyPathTests
+{
+    private static AbLegacyTagCreateParams Params(string cipPath) =>
+        new(Gateway: "10.100.0.35", Port: 44818, CipPath: cipPath, LibplctagPlcAttribute: "micrologix",
+            TagName: "N7:0", Timeout: TimeSpan.FromSeconds(5));
+
+    [Theory]
+    [InlineData("", null)]
+    [InlineData("   ", null)]
+    [InlineData(null, null)]
+    [InlineData("1,0", "1,0")]
+    public void Normalize_maps_blank_to_null_and_keeps_a_route(string? input, string? expected) =>
+        LibplctagPath.Normalize(input).ShouldBe(expected);
+
+    [Fact]
+    public void The_data_tag_omits_the_path_for_an_empty_route()
+    {
+        using var tag = LibplctagLegacyTagRuntime.BuildTag(Params(""));
+        tag.Path.ShouldBeNull();
+    }
+
+    [Fact]
+    public void The_data_tag_keeps_a_real_route()
+    {
+        using var tag = LibplctagLegacyTagRuntime.BuildTag(Params("1,0"));
+        tag.Path.ShouldBe("1,0");
+    }
+}