Inside the System

Autodesk® BIM 360™ the next generation of BIM

Autodesk® BIM 360^TM the next generation of BIM, is for anyone, anywhere, at any time. So what it is it? Well, you may have heard us talk about Autodesk 360, a platform for accessing virtually infinite computing power, enabling building and infrastructure design and construction professionals to more
rapidly design, visualize, simulate and collaborate. BIM 360 is built on the Autodesk 360 platform. 

BIM 360 helps building and infrastructure, design, and construction professionals access intelligent model–based workflows through a broad range of cloud-based services. It puts the project at the center of the BIM process and provides access to cloud based services to help building and infrastructure design and construction teams better predict outcomes on projects, coordinate and collaborate
effectively and solve broad and complex problems.

BIM 360 includes 3 new cloud based services that are launching today: 

      1.  Clash detection, coordination and collaboration

      2.  Field management, commissioning and handover

      3.  Conceptual design and feasibility evaluation 

It also includes existing Autodesk 360 cloud based services that support BIM including:

      -   Rendering

      -  Energy Analysis

      -  Structural Analysis

BIM 360 helps multidiscipline design and construction teams improve project outcomes by moving computational-intensive tasks to the cloud, enabling more rapid visualization and simulation and optimized collaboration with access to intelligent data-rich models. 

Visit the Autodesk BIM 360 page to learn more or follow us on Facebook.

Why do I get different Voltage Drop results with Revit compared to the NEC?

The NEC states table 9 was compiled using the Neher–McGrath ac-resistance calculation method, and the values presented are both reliable and conservative.  The computation is not trivial, and is highly dependent on determining the conductor and insulating materials, and the ambient conditions.  At the bottom of the table, it lists some of the assumptions. 

Further analysis of the data between NEC and Revit shows that Revit is typically more conservative than the NEC.  The table below shows that for a Power Factor of 1.0, Revit is slightly less conservative (that is, Revit will report slightly less drop than using data from the NEC).  However, for power factors from slightly less than 1.0 down to 0.60, Revit will report greater drop (therefore, being even more conservative)... the delta between Revit and the NEC increases as the wire size increases, and as the power factor decreases.

As an example, in the worst case scenario for a 480V three phase circuit, 1000 MCM cable with 0.60 Power Factor, a maximum allowed feeder drop of 2% computed using the R value from Revit would result in a 1.71% drop compared to using the R value from the NEC.  (Our R’s are bigger).  Unless you know exactly the current in a feeder, and know exactly the ambient conditions, the best you can do is use an estimate, inheriting the assumptions such as those provided by the NEC or Revit.  Either way, the result is conservative.

To compute Voltage Drop, why does Revit use the formula VD=(L*R*I)/1000?

... "I’m used to using Table 9 in the NEC for R, and using the formula VD=F*(L*R*I)/1000, where F is 1.73 for three phase circuits, and 2 is for single phase circuits."

Referring to the question in the prior post, you can see that the F factor is already accounted for in the tabular data that Revit uses.  Thus, it is not necessary to multiply by such a factor.

Why does the voltage drop for single phase (single-pole) circuits in Revit seem to be about half what I’m calculating using the NEC R factor, and the formula 2*(L*R*I)/1000?

The 2 in the formula is used to compute Line-to-Line voltage drop.  For a single pole circuit, typically, you account for the Line-to-Neutral voltage drop, which is half of the Line-to-Line voltage drop (and thus, no 2 factor is necessary).  As stated in the documentation, the voltage drop for each circuit is reported as line-to-line for 2-pole (single phase) and 3-pole (three phase) circuits. The voltage drop is reported as line-to-neutral for 1-pole circuits.

Calling All Revit Heroes

Do you have a project that was designed and modeled using Autodesk® Revit for Architecture, MEP and Structure?  Does the building have a unique look that makes it stand out?  If you do… then submit your company name and project to be considered for the Autodesk Revit 2014 hero image! 

We are now looking for next year’s hero image for our Autodesk Revit 2014 products.  The selection process will be based on, but not limited to the following criteria: 

• Is the project modeled using Autodesk Revit for Architecture, MEP and Structure?
• Is the building aesthetically pleasing?  The architectural team needs a building that looks cool and unique to meet their requirements.
• Does the MEP model contain duct, pipe, plumbing and lighting systems?  If it includes cable tray, fire protection, etc., even better!
• It’s not a necessity, but if the structural model contains a good analytical model, it would be a benefit.
• Are all key stakeholders, architecture, MEP and structural engineering firms, including owner, willing to sign an agreement with Autodesk to use their project and models for the purpose of a hero image & other in-product assets such as splash screens?
• Is architect, MEP engineering and structural engineering firms willing to share their design models with Autodesk?  We will need them to create the images using Autodesk 3ds Max Design. 

If you would like to showcase the great work your firm has done and have some bragging rights too, please contact Armundo Darling with the subject line “Revit 2014 Hero Image Submission” to include your company and project for a chance to become the hero image for Autodesk Revit 2014!

Why does the Revit Wire Impedance Factor table have separate sections for Three Phase and Single Phase?

The table published in the documentation provides two sections simply a matter of convenience.  The data in the Single Phase section is the same as that in the Three Phase section, multiplied by the factor 2 / SQRT(3).  As an example, if you look in the first row for #14 in Steel Conduit at a power factor of 60, in the Three Phase section, the value is 3.322 and in the Single Phase section, the value is 3.836.  Multiplying the Three Phase value by the factor yields the value in the Single Phase section: 3.322 * 2 / SQRT(3) = 3.836.