diff --git a/CHANGELOG.md b/CHANGELOG.md
index f1a341398..2a22f5bcb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 ### Changed
+- Changing from comparing strings to comparing uuids in `EntitySource.findFirstEntityByUuid` [#829](https://github.com/ie3-institute/PowerSystemDataModel/issues/829)
+
 
 ## [4.1.0] - 2023-11-02
 
diff --git a/src/main/java/edu/ie3/datamodel/io/source/EntitySource.java b/src/main/java/edu/ie3/datamodel/io/source/EntitySource.java
index eec826f97..d1cfd5c70 100644
--- a/src/main/java/edu/ie3/datamodel/io/source/EntitySource.java
+++ b/src/main/java/edu/ie3/datamodel/io/source/EntitySource.java
@@ -71,19 +71,19 @@ protected String safeMapGet(Map<String, String> map, String key, String mapName)
    *     optional if no matching entity with the provided uuid can be found
    */
   protected <T extends UniqueEntity> Optional<T> findFirstEntityByUuid(
-      String entityUuid, Collection<T> entities) {
+      UUID entityUuid, Collection<T> entities) {
     return entities.stream()
         .parallel()
-        .filter(uniqueEntity -> uniqueEntity.getUuid().toString().equalsIgnoreCase(entityUuid))
+        .filter(uniqueEntity -> uniqueEntity.getUuid().equals(entityUuid))
         .findFirst();
   }
 
   /**
-   * Checks if the requested type of an asset can be found in the provided collection of types based
-   * on the provided fields to values mapping. The provided fields to values mapping needs to have
-   * one and only one field with key {@link #TYPE} and a corresponding UUID value. If the type can
-   * be found in the provided collection based on the UUID it is returned wrapped in a {@link
-   * Success}. Otherwise a {@link Failure} is returned and a warning is logged.
+   * Checks if the requested type of asset can be found in the provided collection of types based on
+   * the provided fields to values mapping. The provided fields to values mapping needs to have one
+   * and only one field with key {@link #TYPE} and a corresponding UUID value. If the type can be
+   * found in the provided collection based on the UUID it is returned wrapped in a {@link Success}.
+   * Otherwise a {@link Failure} is returned and a warning is logged.
    *
    * @param types a collection of types that should be used for searching
    * @param fieldsToAttributes the field name to value mapping incl. the key {@link #TYPE}
@@ -96,7 +96,7 @@ protected <T extends AssetTypeInput> Try<T, SourceException> getAssetType(
 
     Optional<T> assetType =
         Optional.ofNullable(fieldsToAttributes.get(TYPE))
-            .flatMap(typeUuid -> findFirstEntityByUuid(typeUuid, types));
+            .flatMap(typeUuid -> findFirstEntityByUuid(UUID.fromString(typeUuid), types));
 
     // if the type is not present we return an empty element and
     // log a warning
@@ -167,10 +167,10 @@ protected <T extends AssetTypeInput> TypedConnectorInputEntityData<T> addTypeToE
    */
   protected OperatorInput getFirstOrDefaultOperator(
       Collection<OperatorInput> operators,
-      String operatorUuid,
+      Optional<UUID> operatorUuid,
       String entityClassName,
       String requestEntityUuid) {
-    if (operatorUuid == null) {
+    if (operatorUuid.isEmpty()) {
       log.warn(
           "Input source for class '{}' is missing the 'operator' field. "
               + "This is okay, but you should consider fixing the file by adding the field. "
@@ -178,18 +178,16 @@ protected OperatorInput getFirstOrDefaultOperator(
           entityClassName);
       return OperatorInput.NO_OPERATOR_ASSIGNED;
     } else {
-      return operatorUuid.trim().isEmpty()
-          ? OperatorInput.NO_OPERATOR_ASSIGNED
-          : findFirstEntityByUuid(operatorUuid, operators)
-              .orElseGet(
-                  () -> {
-                    log.debug(
-                        "Cannot find operator with uuid '{}' for element '{}' and uuid '{}'. Defaulting to 'NO OPERATOR ASSIGNED'.",
-                        operatorUuid,
-                        entityClassName,
-                        requestEntityUuid);
-                    return OperatorInput.NO_OPERATOR_ASSIGNED;
-                  });
+      return findFirstEntityByUuid(operatorUuid.get(), operators)
+          .orElseGet(
+              () -> {
+                log.debug(
+                    "Cannot find operator with uuid '{}' for element '{}' and uuid '{}'. Defaulting to 'NO OPERATOR ASSIGNED'.",
+                    operatorUuid,
+                    entityClassName,
+                    requestEntityUuid);
+                return OperatorInput.NO_OPERATOR_ASSIGNED;
+              });
     }
   }
 
@@ -212,7 +210,7 @@ protected Stream<Try<NodeAssetInputEntityData, SourceException>> nodeAssetInputE
               // get the raw data
               Map<String, String> fieldsToAttributes = assetInputEntityData.getFieldsToValues();
               // get the node of the entity
-              String nodeUuid = fieldsToAttributes.get(NODE);
+              UUID nodeUuid = UUID.fromString(fieldsToAttributes.get(NODE));
               Optional<NodeInput> node = findFirstEntityByUuid(nodeUuid, nodes);
 
               // if the node is not present we return an empty element and
@@ -265,7 +263,10 @@ protected <T extends AssetInput> AssetInputEntityData assetInputEntityDataStream
       Collection<OperatorInput> operators) {
 
     // get the operator of the entity
-    String operatorUuid = fieldsToAttributes.get(OPERATOR);
+    Optional<UUID> operatorUuid =
+        Optional.ofNullable(fieldsToAttributes.get(OPERATOR))
+            .filter(s -> !s.isBlank())
+            .map(UUID::fromString);
     OperatorInput operator =
         getFirstOrDefaultOperator(
             operators,
diff --git a/src/main/java/edu/ie3/datamodel/io/source/GraphicSource.java b/src/main/java/edu/ie3/datamodel/io/source/GraphicSource.java
index 7cdc097ca..2ecd52c59 100644
--- a/src/main/java/edu/ie3/datamodel/io/source/GraphicSource.java
+++ b/src/main/java/edu/ie3/datamodel/io/source/GraphicSource.java
@@ -150,7 +150,7 @@ protected Try<NodeGraphicInputEntityData, SourceException> buildNodeGraphicEntit
       Map<String, String> fieldsToAttributes, Set<NodeInput> nodes) {
 
     // get the node of the entity
-    String nodeUuid = fieldsToAttributes.get(NODE);
+    UUID nodeUuid = UUID.fromString(fieldsToAttributes.get(NODE));
     Optional<NodeInput> node = findFirstEntityByUuid(nodeUuid, nodes);
 
     // if the node is not present we return a failure
@@ -197,7 +197,7 @@ protected Try<LineGraphicInputEntityData, SourceException> buildLineGraphicEntit
       Map<String, String> fieldsToAttributes, Set<LineInput> lines) {
 
     // get the node of the entity
-    String lineUuid = fieldsToAttributes.get("line");
+    UUID lineUuid = UUID.fromString(fieldsToAttributes.get("line"));
     Optional<LineInput> line = findFirstEntityByUuid(lineUuid, lines);
 
     // if the node is not present we return an empty element and
diff --git a/src/main/java/edu/ie3/datamodel/io/source/RawGridSource.java b/src/main/java/edu/ie3/datamodel/io/source/RawGridSource.java
index b06d55d4d..70c228c96 100644
--- a/src/main/java/edu/ie3/datamodel/io/source/RawGridSource.java
+++ b/src/main/java/edu/ie3/datamodel/io/source/RawGridSource.java
@@ -513,8 +513,8 @@ protected Try<ConnectorInputEntityData, SourceException> buildUntypedConnectorIn
     Map<String, String> fieldsToAttributes = assetInputEntityData.getFieldsToValues();
 
     // get the two connector nodes
-    String nodeAUuid = fieldsToAttributes.get(NODE_A);
-    String nodeBUuid = fieldsToAttributes.get(NODE_B);
+    UUID nodeAUuid = UUID.fromString(fieldsToAttributes.get(NODE_A));
+    UUID nodeBUuid = UUID.fromString(fieldsToAttributes.get(NODE_B));
     Optional<NodeInput> nodeA = findFirstEntityByUuid(nodeAUuid, nodes);
     Optional<NodeInput> nodeB = findFirstEntityByUuid(nodeBUuid, nodes);
 
@@ -621,7 +621,7 @@ protected Try<Transformer3WInputEntityData, SourceException> addThirdNode(
     Map<String, String> fieldsToAttributes = typeEntityData.getFieldsToValues();
 
     // get nodeC of the transformer
-    String nodeCUuid = fieldsToAttributes.get("nodeC");
+    UUID nodeCUuid = UUID.fromString(fieldsToAttributes.get("nodeC"));
     Optional<NodeInput> nodeC = findFirstEntityByUuid(nodeCUuid, nodes);
 
     // if nodeC is not present we return a failure
diff --git a/src/main/java/edu/ie3/datamodel/io/source/SystemParticipantSource.java b/src/main/java/edu/ie3/datamodel/io/source/SystemParticipantSource.java
index 3754362dd..d00f4e37a 100644
--- a/src/main/java/edu/ie3/datamodel/io/source/SystemParticipantSource.java
+++ b/src/main/java/edu/ie3/datamodel/io/source/SystemParticipantSource.java
@@ -928,12 +928,15 @@ protected Try<ChpInputEntityData, SourceException> buildChpEntityData(
     Optional<ThermalStorageInput> thermalStorage =
         Optional.ofNullable(fieldsToAttributes.get(THERMAL_STORAGE))
             .flatMap(
-                thermalStorageUuid -> findFirstEntityByUuid(thermalStorageUuid, thermalStorages));
+                thermalStorageUuid ->
+                    findFirstEntityByUuid(UUID.fromString(thermalStorageUuid), thermalStorages));
 
     // get the thermal bus input for this chp unit
     Optional<ThermalBusInput> thermalBus =
         Optional.ofNullable(fieldsToAttributes.get("thermalBus"))
-            .flatMap(thermalBusUuid -> findFirstEntityByUuid(thermalBusUuid, thermalBuses));
+            .flatMap(
+                thermalBusUuid ->
+                    findFirstEntityByUuid(UUID.fromString(thermalBusUuid), thermalBuses));
 
     // if the thermal storage or the thermal bus are not present we return an
     // empty element and log a warning
diff --git a/src/test/groovy/edu/ie3/datamodel/io/source/EntitySourceTest.groovy b/src/test/groovy/edu/ie3/datamodel/io/source/EntitySourceTest.groovy
index b2881dbdf..4b51be15b 100644
--- a/src/test/groovy/edu/ie3/datamodel/io/source/EntitySourceTest.groovy
+++ b/src/test/groovy/edu/ie3/datamodel/io/source/EntitySourceTest.groovy
@@ -48,7 +48,7 @@ class EntitySourceTest extends Specification {
         )
 
     when:
-    def actual = dummyEntitySource.findFirstEntityByUuid(uuid.toString(), entities)
+    def actual = dummyEntitySource.findFirstEntityByUuid(uuid, entities)
 
     then:
     actual.present
@@ -58,7 +58,7 @@ class EntitySourceTest extends Specification {
   def "A CsvDataSource should always return an operator. Either the found one (if any) or OperatorInput.NO_OPERATOR_ASSIGNED"() {
 
     expect:
-    dummyEntitySource.getFirstOrDefaultOperator(operators, operatorUuid, entityClassName, requestEntityUuid) == expectedOperator
+    dummyEntitySource.getFirstOrDefaultOperator(operators, Optional.of(UUID.fromString(operatorUuid)), entityClassName, requestEntityUuid) == expectedOperator
 
     where:
     operatorUuid                           | operators                | entityClassName   | requestEntityUuid                      || expectedOperator