Revit MEP Circuiting

I created a short video that describes the basic interaction between electrical devices and creating a circuit. It's really meant to help explain what happens when a device is already assigned to a circuit and we select it along with other elements that aren't circuited. The ribbon changes based on our selection and a circuited devices impairs our ability to create a circuit for the other devices that are eligible to create one.

• A device that is not part of a circuit, when selected by itself, will cause the Power button to appear
• A device that is part of a circuit, when selected by itself, will display the additional Electrical Circuit tab
• Multiple devices that are both part of a circuit and not part of circuit will only display the context ribbon relevant for the devices, no circuit tab or power button
• Selecting multiple devices that are assigned different electrical requirements will disable the Power button

When we select devices we need to be sure to glance at the ribbon for clues. Here's a video (no audio, turn on Captions).

I also wrote an earlier post about circuits if you're interested.

Load Classifications and Worksets

The early releases of Revit MEP didn't have a method to manage load classifications, they were hard wired (pun intended). It does now.

One downside of various sources of content is the way the family editor (person) assigns the load classification. It can be hard coded into the family (not nice), it can be assigned to a parameter instead (nice) and it can also be assigned a value in advance too (nice or not nice depending on who you are).

Load classifications are part of the project standards workset.

If you choose to be the "owner" of the electrical related project standards and not relinquish them there is still a back door that lets a new family introduce a load classification you may not approve of. Revit only seems to acknowledge ownership if you attempt to alter the existing settings, and that's only true if someone else has decided to make themselves the owner of the workset (Electrical Load Classifications). Loading a new family that has a classification like "Steve's Favorite Motors" will bring it along and add it to the load classifications.

This means trying to keep a handle on your load classifications can be a little troublesome has the project progresses. The electrical design team might behave but all it takes is a rogue HVAC user to load a new single duct VAV, that has its own notion of load classification, into the model (assuming multiple trades in one file).

Further, I think its odd that when I create a new Load Classification (like Steve's Favorite Motors) none of the electrical setting worksets show me as the borrower, especially the one called Electrical Load Classifications! If I change the load classifications I still am not considered a borrower, odd. What is odder still is that the worksets for Cable Tray Settings, Cable Tray Sizes, Conduit Settings, Wire Settings and Wire Sizes DO show me as borrower.

I understand that it might be better to let a family load completely and "sneak" in a new load classification than confront the user with a message about not being able to make a workset editable and refusing to load the family.

Best bet is to require content to be vetted for load classifications before they are added to the project model(s). Provide a list of classifications that the project electrical engineer wants to document. Also provide a set of "in this case, use this classification" examples to make it easier to tow the line.

Panel Schedule and Load Calculation Addition

A thread at AUGI that started in December 2011 described a situation that Panel Reports show some connected loads as "0". The thread wandered around a bit but Martin Schmid with Autodesk responded on Tuesday with some insight after the development team did some research. Martin prepared a video to help explain what can cause this.

He wrote in his reply at AUGI:

I was able to reproduce this today with some help with our development team. The issue seems to be related to having your connector's Load Classification Parameter associated with a Parameter that has an empty value specified.

You can see in the video that when I create a Load Classification parameter, it has no value... when I then associate that with the connector, the connector ends up with a load classification with no value. Thus, when you connect this, there is no value that propegates into the panel totals, since the panel totals are dependent on summing values from load classifications. As soon as I set a value on the parameter associatd with the connector's Load Classification, the values tabulate.

A reply at AUGI shortly thereafter reminded members to also check the Part Type setting for their families. Using stock content it isn't likely that this would be the issue but for any custom content that has been downloaded or created internally, checking everything you can won't hurt.

Electrical Panel Load Calculations

Another "inside" gem from Inside the System which offers deeper insight to how the numbers work. If you are a Revit MEP user and electrical is your game, then you'll want to read it. Thanks to Martin for taking the time to put it together.

Revit MEP Electrical Calculations

Martin Schmid has been sharing some deeper insight into the "magic" behind electrical calculations that Revit provides. Every engineer I've met is, not too surprisingly, skeptical about trusting yet another software for these answers. There has been data, in help documentation, to support the results but not quite as deeply as the last three posts combined. Check them out!

Why do I get different Voltage Drop results with Revit compared to the NEC?
To compute Voltage Drop, why does Revit use the formula VD=(L*R*I)/1000?
Why does the Revit Wire Impedance Factor table have separate sections for Three Phase and Single Phase?