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Efficient Xref Management for AutoCAD Plant 3D

By on January 13, 2014 in AutoCAD Plant 3D, Autodesk, Featured, News, Your Plant Buddy with 2 Comments

Jarrod Mudford


A successful 3D Model in AutoCAD Plant 3D relies on many efficient foundations. One of these foundations is Xref Management within your project. There is countless number of times that I come across projects that have a poorly managed xref system and the consequences from such a system can cause delays in your project design phase.

Break down the models of your project

Firstly, we need to work out how to break down the models of your project. Some projects are small and may not require as much break down. But what if a smaller project becomes a larger project at a later date? We want to develop a scalable model referencing system that ensures productivity throughout the lifecycle of the models. Remember, you may be awarded a project in following years to add-on to what you have already designed. Breaking down the models to manageable sizes is always a good practice. See last month’s blog for more information on model sizes here.

Number of Designers

The first thing I take into consideration when breaking down your models is the number of designers you have working on the project. It is not going to work if you have 10 designers with 8 model files. 2 people will not have any files available to work on. And even if you had 10 models available, it also means each individual designer has control of a model, stopping users from access other models immediately.
I look at a ratio system of designers to models. If I have 10 designers and 100 models, I have a 1:10 chance of two designers wanting to access the same file at the same time. But also make sure you think for the future of the project. What happens if at the end of the project you need to resource the project with more designers? That ratio is going to fall. Same goes if the project develops into a larger project.

Model Efficiency

Secondly, I look at the efficiency of models being opened up on a PC. It’s inevitable that large model files are going to take longer to open on your PC. So having design files and master files is necessary to ensure that users only need to open design files to do any design work. The purpose of the Master Files is to act as a container of the Design Files for a particular service, area, or discipline etc. Typically when I set up a project, I strive to set up all the files that will be required in the project. This is possible if you have an xref and model management system for your project. The reason I do this is for two reasons. The first reason is that it takes away the thought process a designer would have to go through when creating a new dwg model file. They will be thinking, where do I save this file? What do I save it as? Where do I xref it? What xref type do I use? And the second reason is that when I am setting up the master files, I can xref the design files much quicker because there is no data contained in them yet.

The purpose of having Master Files set up at the early stages of the project, is not just for speed, but to efficiently update any xrefs that contain these master files. For example, if you had ten designers all working in one area of the project, and they created two new files each a day, which is going to be 20 times the Master File is going being accessed to add in a file that was already planned to be there. And if we then look at the issue of the Master File try to be accessed by multiple users, it won’t take long for access issues to become evident.

Master files are created for each discipline, area, service or whatever works for your project. The Master Files are used in the Master File at the next level and so on. They can also be used as a cross reference, (overlay), to other disciplines or areas etc. By utilizing the Master Files in other Disciplines, Areas, or Services, the file will continually update to ensure the latest information is available. We don’t want a user overlaying 100 files into their model file.
The files that are created for the project are not just limited to AutoCAD Plant 3D, this system can be applied to other applications also.
Here is a quick example of a project that has a scalable Xref Structure.


Use Project Manager Folders

Using folders in the Project Manager is the best way to organise the files into manageable sets. Each folder represents an Area and a Discipline. In each of the Discipline folders is each of the dwg Model Files, including a Master Model for that specific discipline.
In the Area folders are the Discipline Folders and a Master Model file for that area. This system is followed throughout the project.


For the Equipment Master Model file, I have attached the individual Equipment Design Files.


For the Piping Master Model file, I have attached the individual design files of the pipes. Note here that I have named the files by line number, where each line number, for Area 1 has its own file. This is becoming more common as users are realizing the effects of having too fewer files in their project. Another system that is becoming more common is to use the service or spec as the breakdown of the piping files.


All Model Files

Here I have attached all the Master Model Files from each Discipline folder to the Master Model for the Area. Note here that it will also list the files contained in each of the Discipline Master Files.


As an example for a design file, I have opened the Piping Design File for line number 1001. Because I needed to connect to equipment in Area 1, I have overlayed the Equipment Master Model. I haven’t used the Equipment Design Files as there could be a lot of files, and the single Master Model File contains everything that is attached. This way, if someone is to add a new file to the Equipment Master Model, it will be automatically included into Pipe Design file number 1001.


When appending files to Navisworks, you can append the dwg model files directly. This will create its own associated .nwc files, (There is no requirement to export to nwc). The created nwc files will be time stamped against the dwg file that it was created from. So any time a refresh or an open is done on the Navisworks, (nwf), file it will check for any updates. The updates will happen automatically. Because everyone is opening the same Navisworks file, everyone will be updating the files which will improve productivity upon opening for others.
For this to work though, it is best for the design files to be appended to Navisworks, as the only way a Master Model file will be updated, is if someone opens the Master Model file and saves it.
With that said, let’s look at the downfalls if you were to use the Master Model file in Navisworks; firstly, if you have 10 designers all working in the same area. Every time, they make a Design model change, for it to be seen in Navisworks, they will need to open the Master Model. There will most likely be a wait time for the Master Model to open due to its size. If each designer had to open the file twice a day, and it took 15 minutes each time, (it is common), that equates to 5 hours of waiting time each day. 25 hours a week, and 1300 hours per year. It’s a large cost to think about.
There is a large amount of files added to Navisworks, but it pays off after they have all being added. A common task for me, is setting up the Navisworks file, with appended dwg files when they are empty. It is quicker, and although the Navisworks file is empty, as soon as the Project Manager or Engineers open the Navisworks file, it shows the latest model information. If there are no models, then they are well aware that the project has not reached that stage in the design phase. 

Workflow Diagram

Here is a flow that I typically use for xref structure. This image shows a common xref structure utilized in many organizations to ensure an efficient AutoCAD Plant 3D project. Remember the general rules of xref’ing. Always “Overlay” down or across the structure. Only “Attach” up the structure. Across the disciplines is also necessary to use “Overlay”.



If you want any further information or you need help on site, feel free to contact me at or just leave a comment below. Cheers!

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There Are 2 Brilliant Comments

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  1. Jason Drew says:

    Excellent article Jarrod. Thank you for sharing!

  2. Marchand says:

    Hi Jarrod,

    I realize this is quite an old post, but I’m trying to adapt to the suggested method but am finding trouble with xrefs.

    My first problem is circular references (because of layout planning I need to overlay certain files) and second problem is lines connecting to other xrefed lines do not display correct in the Iso generated… it just registers open ends or the BOM becomes screwy as the connecting line’s items appear itemized in the BOM…

    Hope you read this thread and can give me some guidance as to what I’m doing wrong…

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