There are two entities that develop electrical drawings in a construction project: the engineer of record (EOR) and the installing contractor. Although addressing the same electrical systems in the same areas of a building, the drawings developed by the two groups look very different because they serve different functions. The EOR main role is to design an installation that is safe and compliant with the applicable codes and standards. The contractor role is to figure out the most effective method to install what was designed by the EOR.
The question that a facility manager faces is: which electrical drawings are most useful to keep and which group will have the most accurate information.
Here is the breakdown:
1. One-line diagram and panel schedules
These drawings are the skeleton of the electrical system and they should be identical from EOR and the installing contractor. The field installers usually red mark the drawings and the engineering company incorporates the field modifications in the design, verifying that the installation still complies with the codes and design intent. If this process was followed, EOR should have the most up-to-date version of these documents at construction completion.
2. Power systems studies
The power system studies that are usually requested for new construction are:
a. Short Circuit Study – to prove the equipment can sustain the available fault current
b. Overcurrent Protection Coordination Study – to prove that the electrical system is selectively coordinated; meaning that in case of a fault, the closest device to a fault will open without unnecessarily interrupting power in other parts of the electrical distribution system.
c. Arc Flash Evaluation – to indicate the possible arc flash energy and recommended protective equipment rating at each panel and switchboard.
These studies are done with the aid of complex software that requires as main input the overcurrent protective devices types and settings, material and lengths of feeders. This information is most accurate from the installing contractor.
3. Power and lighting plans
The EOR identifies all fixtures and equipment requiring electrical connections, and develops floor and ceiling plans allocating circuits in panels and connecting electrical loads together. The end of the circuit is usually shown with a “home run”, noting the panel and circuit number but omitting the routing to the panel. This way the installing contractor can choose the best routing to the panel. If the circuit designation changes during construction, the contractor submits red lines that are reviewed and incorporated in the record documents by EOR.
4. Large conduit routing – underground and concealed in overhead
These drawings are developed by the installing contractor and show conduit layout and supports for the overhead, and conduit depth and duct bank sections for the underground. It is useful for future developments to know the general area where conduit is buried or concealed. If the contractor used a total robotic station to layout the underground conduit, they can provide the exact coordinates of layout points and the control points used.
5. Construction Operations Building Information Exchange (COBie) data
COBie helps the project team organize electronic submittals approved during design and construction and deliver a consolidated electronic O&M manual. COBie data may then be imported directly into Computerized Maintenance Management Systems (CMMS) and asset management software, at no cost. Installing contractors have the exact information of the equipment installed including the warranties responsible parties and start dates.
6. Electrical BIM model
Engineers and architects develop BIM models and coordinate in design phase using a structural design model and generic equipment sizes for the building systems. The construction models, on the other hand, are more accurate because they are based on the structural fabrication model and the specific equipment purchased by the contractor. The electrical model is useful only if is incorporated in the aggregated model of the facility.
EDM Incorporated has provided electrical engineering services as the EOR for a variety of projects. Our services include BIM modeling, existing conditions assessments, electrical load analysis, power and lighting design, and energy efficiency recommendations. Please contact us if you would like to discuss how we can assist with your next project.