In Autodesk Revit, the Collaborate tab provides the tools necessary for managing multi-user worksharing environments. The Synchronize with Central command allows users to save their local changes back to the central model. However, this command becomes disabled under certain conditions --- most notably when the user is currently working directly within the central file rather than a local copy.

The Autodesk Revit User's Guide -- Worksharing and Collaboration section clearly explains this behavior:

''When you open the central file directly, the Synchronize with Central option is unavailable because all edits are already in the central file. Worksharing operations such as borrowing, relinquishing, or synchronization only apply to local copies created from the central model.''

This rule ensures that the integrity of the central model is preserved and that no user directly edits or synchronizes within it, preventing potential file corruption. In normal collaborative workflows, users open local copies of the central model. The local files maintain an editable subset of elements while allowing synchronization and relinquishing operations.

Thus, the disabled Synchronize with Central button (as shown in the exhibit) indicates that the designer is currently in the central model, not a local copy. Since synchronization is unnecessary in this state --- all changes are automatically applied to the central file --- the command is grayed out.

To allow conduit to be modeled from any point on a specific side of the electrical equipment, the most accurate method is to use the 'Surface Connector'. This method enables the designer to place a surface-based conduit connector on a specific face of the equipment family. Here's how the process is explained:

'To place a conduit connector on the surface of a family component so that the conduit can start from anywhere on that surface, use the Surface Connector option. This connector attaches to the selected face of the equipment, allowing conduit to be drawn directly from any point on the selected face in the project environment.'

'Click Conduit Connector, then choose Surface Connector, and select the face where the conduit should connect. This gives flexibility in modeling, especially for equipment requiring multiple connection points across a single face or allowing freedom of routing.'

This process is especially beneficial in custom electrical equipment families where conduits must originate from arbitrary points along a flat side---ensuring both parametric flexibility and coordination ease within the project environment.

In contrast:

Option A refers to editing connector dimensions, which does not affect the connector's ability to accept connections from any surface point.

Option B uses Individual Connector which limits the connection to a specific point, not the whole face.

Option D refers to changing connector type in the Properties palette, which doesn't impact connector location or coverage on a face.

Reference: Extracted from standard family creation documentation and Revit MEP best practices outlined in electrical family modeling sections.

In Autodesk Revit Electrical Design, when an electrical designer needs to directly connect Panel B to Panel A without a breaker---such that Panel A's load includes the total load from Panel B---the correct method is to configure both panels to use the same distribution system and to set Panel B's connection type to Feed Through Lugs.

According to the Autodesk Revit MEP User Guide, Chapter 17: Electrical Systems, under ''Creating Power and Lighting Circuits'' and ''Panel Properties'' sections:

''When connecting panels in series, ensure both devices share the same distribution system. If a subpanel is required to pass its total load through to another panel without circuit protection, specify the connection type as Feed Through Lugs. This connection allows the upstream panel to include the total connected load from the subpanel in its own load summary.''

The feed-through lugs configuration enables the second panel (Panel B) to be electrically tied to the first (Panel A) as though it were an extension of the same bus. Unlike breaker or main-lug-only setups, the feed-through configuration does not insert a protective breaker between the two panels. Instead, it provides a continuous feeder connection where the parent panel's load schedule automatically aggregates the downstream panel's total load.

This setting is found in Revit's Properties Palette for electrical equipment:

Under Electrical - Circuiting, the designer must ensure both panels use the same Distribution System (e.g., 208Y/120V 3 4W).

Then, under Connection Type, select Feed Through Lugs.

The Smithsonian Facilities Revit Template Electrical Standards Guide also confirms this best practice:

''Feed-through panels are used when a subpanel's total load must be reported in the main distribution panel without additional breakers. Both panels must share identical voltage and phase configurations within the same distribution system.''

Why the Other Options Are Incorrect:

A . The ''subfeed lug breaker'' introduces a breaker, contradicting the requirement of no breaker.

B . ''Circuit subfeed panel type'' is not a standard Revit configuration; Revit uses connection types instead.

D . Transformers alter the voltage distribution; the question specifies a direct connection within the same system.

Therefore, the correct configuration that meets all design and load reflection requirements is: C. Both panels are assigned to the same distribution system, and the connection type is set to feed through lugs.

References:

Autodesk Revit MEP User Guide -- Chapter 17 ''Electrical Systems,'' Sections: ''Creating Power and Lighting Circuits'' and ''Panel Properties,'' pp. 420--426

Autodesk Revit Electrical Design Essentials -- Topic: ''Feed-Through Connections and Subpanel Load Reflection''

Smithsonian Facilities Revit Template User's Guide -- Section 9.3 ''Panel Configuration and Feed-Through Connections,'' p. 96

In Autodesk Revit MEP Electrical Design, the System Browser is used to analyze and verify electrical systems, including panelboard connections, circuit hierarchies, and connected loads.

From the exhibit, the Properties palette shows that the selected equipment is a Lighting and Appliance Panelboard (208V MLO, 100A), named P4. To determine the parent panel that feeds Panel P4, we refer to the System Browser, which organizes the entire electrical distribution network hierarchically under the Electrical discipline.

In the System Browser on the right, under the Electrical category, we can observe that Panel P4 is nested directly under Panel P2. This organization indicates that P4 is circuited to (or fed from) Panel P2.

According to the Revit MEP 2011 User's Guide, Chapter 4, ''Electrical Systems---Using the System Browser,'' it states:

''The System Browser displays electrical systems in a tree structure. Each subpanel or device listed beneath a main panel is connected to that panel through an electrical circuit. When a panelboard appears under another, it indicates the subpanel is fed from that parent panel.''

This is further reinforced in Smithsonian Facilities Revit Electrical Template Documentation (April 2021), Section 8.3 ''Documentation Views,'' which describes:

''Panel schedules and browser hierarchies show the distribution sequence. Subpanels appear indented beneath their source panel, indicating electrical dependency and circuit assignment.''

Therefore, by interpreting both the Revit interface and Autodesk's documentation, Panel P4 is a subpanel connected to Panel P2, confirming that its electrical feed is assigned from Panel P2.

Final Verified Answer: B. Panel P2

Reference Sources:

Autodesk Revit MEP 2011 User's Guide, Chapter 4 --- Electrical Systems and the System Browser

Smithsonian Facilities Revit Template User's Guide, Section 8.3 --- Electrical and Fire Alarm Templates: Documentation Views

According to Autodesk's Revit MEP User's Guide (Revit MEP 2011, Chapter 17 ''Electrical Systems''), lighting fixtures in Revit are hosted components---this means they rely on another model element (like a wall, ceiling, or floor) to exist. Specifically, ceiling-hosted lighting fixtures must be placed on a ceiling element that is within the same model file in which the light is being placed.

From the document:

''Most lighting fixtures are hosted components that must be placed on a host component (a ceiling or wall). To place a lighting fixture in a view:

In the Project Browser, expand Views (all) Floor Plans, and double-click the view where you want to place the lighting fixture.

Click Home tab Electrical panel Lighting Fixture.

In the Type Selector, select a fixture type.

On the ribbon, verify that Tag on Placement is selected to automatically tag the fixture.

Move the cursor over the drawing area. The lighting fixture is previewed as you move the cursor over a valid host or location in the drawing area.

Click to place the lighting fixture.'' --- Revit MEP User's Guide, Chapter 17: Electrical Systems, p. 402

Additionally, in the Rendering section of the same guide, Autodesk clearly defines hosting relationships in lighting fixture templates:

''The names of all lighting fixture templates include the words Lighting Fixture. Be sure to select the appropriate template for the type of lighting fixture that you want to create. For example, to create a ceiling-based fixture for metric projects, use Metric Lighting Fixture ceiling based.rft. Revit MEP opens the Family Editor. The template defines reference planes and a light source. For ceiling-based and wall-based fixtures, the template includes a ceiling or wall to host the fixture.'' --- Revit MEP User's Guide, Chapter 50: Rendering, p. 1148

This indicates that the ceiling host must physically exist within the same model environment. If the ceiling is part of a linked architectural model, the lighting fixture cannot attach to it directly because Revit does not allow cross-model hosting. In such cases, a work plane-based or face-based light family must be used instead.

Therefore, among the given options:

A (snapping using nodes) and B (hosted to a ceiling reference plane) are partial actions within a placement workflow, not hosting conditions.

C (defined in the ceiling layout pattern) is incorrect because pattern layout does not determine hosting.

D (placed in the same model as the ceiling) is correct since Revit requires the ceiling host and the light fixture to exist in the same project file for the hosting relationship to function.

Verified Reference Extracts from Revit for Electrical Design Documentation:

Autodesk Revit MEP User's Guide (2011), Chapter 17: Electrical Systems, p. 402 --- ''Most lighting fixtures are hosted components that must be placed on a host component (a ceiling or wall).''

Autodesk Revit MEP User's Guide (2011), Chapter 50: Rendering, p. 1148 --- ''For ceiling-based and wall-based fixtures, the template includes a ceiling or wall to host the fixture.''

Revit MEP Family Templates Description --- Metric Lighting Fixture ceiling based.rft defines the ceiling as the hosting reference within the same model environment.