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It costs money to use BIM on a project, and it’s natural to weigh costs and benefits to get the best outcome. Electrical systems have the reputation for being the most flexible in the practice of BIM, which results in electrical systems receiving the least attention during preconstruction. For example, electrical is most likely to have the lowest level of development (LOD) in BIM execution plans and is most likely not to be modeled by project designers before subcontractors are engaged.
The perceived flexibility of electrical systems in BIM is flawed and incorrect. Here are three reasons we believe you should think differently about electrical modeling in 3D:
- Inflexibility first…
Electrical systems include more than just conduits, and the non-conduit systems are some of the least flexible systems in a project. For example, cable tray is unique in that it takes up a large amount of space and has practical clearance zones both above and below it; if you can’t install cable into the tray, it doesn’t really serve the purpose. Electrical panels have a code-required clearance in front and above them. Bus ducts are a long lead-time item and have limited ability to change elevation. A final example would be exotic systems like fiber optic pathways for data, which have very large bend radii and are nearly completely inflexible. While conduits are the majority of routing, these other electrical systems are some of the most inflexible.
- Conduits like friends
In BIM specifications, it is very common for the electrical requirement to be written like this: Electrical conduit systems 2″ and larger will be modeled.
The common thinking is that conduit systems are flexible because they can be bent at any angle. Language like this removes the necessity to model every single conduit, decreasing the BIM budget for the electrical trade. After all, conduits are difficult to model, and since they are so flexible, they can just go around other trades.
But it isn’t efficient to run conduits alone. Conduits are routed in tight groups with a minimum amount of spacing between them so they can use the same rack for support. As soon as you have more than one conduit, you’re spatially bigger than 2 inches, which is often the lower bound for electrical modeling. The system that is commonly believed to be flexible is now grouped with many others, and it takes significant labor to get those conduits to adjust their elevation or centerline. One conduit is flexible; multiple conduits are not flexible.
Some BIM execution plans have adapted to say that it’s best to model conduits “when grouped.” Conceivably, this means that once conduits branch off from the main run, they no longer have to be modeled. In effect, this would show that no conduit actually connects to any equipment, panels, or fixtures. While this may be acceptable from a coordination point of view, it neglects another important element…
- Electrical models in facilities management
Facilities management (FM) uses of BIM focus on models for maintenance and operations. Electrical systems are an important part of FM. Equipment with electrical is more likely to be equipment that needs maintenance; electrical is one of the first things to troubleshoot if there’s an equipment problem, and the ability to retrofit is often constrained by electrical requirements. If we followed the common BIM scope and didn’t model conduits all the way to equipment, we significantly shortchange the ability of facilities managers to use the model.
While electrical is perceived to be flexible, it turns into a major coordination challenge prior to construction because the perception doesn’t match actual usage.
What’s the solution?
At BuildingSP, we’ve created GenMEP, which reduces the modeling time of mechanical, electrical, and plumbing (MEP) systems. For electrical, conduits are routed clash-free by simply selecting a start point, an end point, and parameters.