The model is finished, the sheets are printed, and the installer still asks the same questions: how wide is this tray, what is that board called, is the circle on the ceiling a light or a smoke detector. Nothing is missing from the model. What is missing is the layer of text and symbols that can be read on paper.
MEP symbols in Revit are not one thing but three separate layers: the linework drawn inside the equipment family, the tag that reads a parameter off the object, and the legend that explains what each symbol means. This article walks through fifteen steps in Revit 2027 with a screenshot at each one, and ends with the Vietnamese standard numbers that are still in force. For the documentation workflow end to end, the Institute runs a Revit MEP course.
MEP symbols in Revit live in three different layers
The three layers behave differently, and mixing them up is why people edit the wrong thing for an hour.
| Layer | What it is in Revit | Where you edit it |
|---|---|---|
| Family linework | 2D lines drawn inside the family, carried by the object, switched by Detail Level | The Family Editor of that family |
| Tag | A separate annotation family that displays one parameter of the object | Edit Family on the tag, or the parameter on the object |
| Legend | A legend view holding symbol images and explanatory text | The legend view itself |
The tag is the only layer that carries live data: change the tray size and the label follows. Family linework is fixed, and the legend is a lookup table you build yourself.
| What you want to do | Ribbon path in Revit 2027 |
|---|---|
| Label one object | Annotate › Tag › Tag by Category |
| Label everything at once | Annotate › Tag › Tag All |
| Place a free-standing symbol | Annotate › Symbol |
| Create a legend view | View › Create › Legends › Legend |
| Pull a symbol image into the legend | Annotate › Detail › Component › Legend Component |
| Give each service its own linework | Manage › Additional Settings › Line Styles |
The file used here
Everything below is built on a copy of the Institute electrical sample file linked to the Snowdon Towers architectural model that ships with Revit; the two files are put together in the article on the Revit MEP sample file. You need a floor plan that already has cable tray, conduit and one electrical panel. Plain text, text types and Vietnamese fonts belong to the article on tags in Revit.
Check what the project already has
Step 1 — Open the service plan and read the view scale
Open the floor plan of the service you are documenting and read View Scale in the Properties palette. Annotation text is sized on paper, so the scale decides how large every label looks. Set the scale first, tag afterwards.
Step 2 — Read the Loaded Tags And Symbols table
Go to Annotate, click the arrow on the Tag panel title and pick Loaded Tags And Symbols. Type a word into Category name search, for example Electrical, to filter the list. The Loaded Tags column shows which tag family each category is using.
An empty column is normal. The Revit installer no longer ships the Autodesk family library; the library folder only holds a file that points you to the online content.
Step 3 — Load tag families from the online content
Go to Insert › Load Autodesk Family. In the Browse column open Annotations, then Electrical. Tick the box on each tile to select several families at once, for example Cable Tray Size Tag, Conduit Size Tag and Electrical Equipment Tag, then click Load.
Open Loaded Tags And Symbols again to confirm: any category that now shows a family name in the Loaded Tags column is ready to tag.
Tag the cable tray, the conduit and the panel
Step 4 — Start Tag by Category
On Annotate, click the arrow under Tag. The menu holds two commands: Tag by Category labels whatever category you click on, and Tag by Example works from tags already placed, the status bar asking you to click the example tags and press Enter to finish.
Step 5 — Set the leader and the text direction on the ribbon
As soon as the command runs the ribbon switches to the Modify | Tag tab, and the tag options sit there rather than on the Options Bar. Leader Line turns the leader on and the box beside it holds its length. Orientation switches the text between horizontal and vertical, and Angle rotates it.
Step 6 — Click the object to place the label
Hover over the object until it highlights, then click. The click point is where the label lands and the leader draws itself back to the object. A cable tray tag reads the tray size straight from the model, so resizing the tray rewrites the text.
Click an object whose category has no tag loaded and Revit asks straight away with the No Tag Loaded box. Answer Yes to load one now, or No and go back to step 3.
Step 7 — Label everything at once with Tag All
Go to Annotate › Tag › Tag All. In the Tag All Not Tagged dialog choose All objects in current view, tick the categories you need in the Category column, tick Leader if you want leaders, then click OK. The Loaded Tags column tells you which family each category will use.
Objects that live in a linked model are only tagged when Include elements from linked files is ticked. Forgetting that box is why the architectural lights and fixtures come back with no labels.
Step 8 — Pull the overlapping labels apart
Tag All puts every label at the same offset, so wherever two objects sit close together the two labels land on top of each other. Select a label and drag it into clear space; the leader stretches and still points at the same object.
Fix the revit tag family when the label reads the wrong thing
Step 9 — Select the label and click Edit Family
A question mark means the parameter the label reads is empty on the object. To find out which parameter that is, select the label and click Edit Family on the Mode panel of the Modify | Electrical Equipment Tags tab.
Step 10 — Read the Edit Label dialog
In the Family Editor click the label, then click Edit Label on the Modify | Tag Label tab. The Label Parameters table on the right lists the parameters the label reads. To add another one, pick its name in the list on the left and click the green arrow between the two columns.
When you are done click Load into Project and Close. If you do not want to keep the change, close the family and answer No in the Save File box.
Step 11 — Fill in the parameter on the object
The quicker route is to leave the family alone and fill the parameter. Select the panel, scroll the Properties palette down to Identity Data, type the board name into Mark and click Apply. The question mark is replaced by the name at once.
Which route you take depends on the job: filling a parameter fixes one object, while editing the label changes what every label of that type reads across the whole project.
Build a revit legend view for the drawing set
Step 12 — Create the legend view
Go to View › Create › Legends › Legend. The New Legend View box asks for a Name and a Scale. Annotation text has a fixed size on paper while the symbols scale with the view, so at 1:50 the symbols end up smaller than the text; a symbol legend belongs at 1:10 or 1:20.
Step 13 — Pull the symbols in with Legend Component
The legend opens empty. Go to Annotate › Detail › Component › Legend Component, the same path the Autodesk page on legend views gives. The Placement panel has three boxes: Component Type picks the family and has its own search box, View Direction picks the view direction, and Host Length sets the sample length for anything that runs.
What lands on the sheet is the family's own symbol, not a picture of it. Redraw the family and the legend follows, so the legend never drifts away from the drawings.
Step 14 — Add annotation symbols and the wording
Symbols that belong to no model object, a direction arrow for instance, are placed with Annotate › Symbol. The wording beside each symbol is placed with Annotate › Text. Keep symbols in the left column, text in the right, one block per service.
A legend is the one view type you can drop onto several sheets without duplicating it, unlike a floor plan. Laying out and printing the set is covered in the article on MEP sheets in Revit.
Step 15 — Give each service its own linework
Line weight and pattern should differ by service. Go to Manage › Additional Settings › Line Styles, add a style, set its weight, colour and pattern, then draw annotation linework with that style.
Revit electrical symbols and the Vietnamese standards
This is where many drawing sets copy the wrong number. The codes printed in the corner of a legend are usually standards that have been withdrawn. The table below is read from the portal of the Vietnam Standards and Quality Institute.
| Number | Full title | Status |
|---|---|---|
| TCVN 7922:2008 | Graphical symbols for diagrams | In force, identical to IEC 60617:2002 |
| TCVN 185:1986 | Design documentation system – Graphical symbols on electrical diagrams – Electrical equipment and wiring on plans | Withdrawn, replaced by TCVN 7922:2008 |
| TCVN 6077:2012 | Building and civil engineering drawings – Simplified representation of technical equipment | In force, replaces TCVN 6077:1995 and TCVN 4615:1988 |
| TCVN 5040:1990 | Fire protection equipment – Graphical symbols for fire protection plans | Withdrawn, identical to ISO 6790:1986 |
Three practical readings. Electrical symbols on schematics come from TCVN 7922:2008, not from TCVN 185. Symbols for water supply, drainage, ventilation and heating equipment fall inside the scope of TCVN 6077:2012. Fire protection has no symbol standard in force at all, so a fire legend should say it follows office practice rather than claim a standard.
The families shipped with Revit are drawn to North American habit and do not match the symbols a Vietnamese reviewer expects. The practical answer is to take the local symbols from your office template and draw the missing ones in the Family Editor, as in the article on MEP equipment families.
From AutoCAD symbol blocks to Revit
People coming from CAD look for a block library of sockets, boards and fittings to insert. Revit does not work that way, and this is the translation table.
| In CAD | In Revit |
|---|---|
| A block for a socket, a light, a board | A family; the symbol is linework held inside it |
| Block attributes edited with ATTEDIT | Object parameters, printed on the sheet by a tag |
| A legend drawn by hand with lines and text | A legend view with Legend Component |
| Layers carrying the linework of each service | Line Styles and view filters |
| A lisp routine counting blocks | A schedule reading the model directly |
Old DWG sets are still usable: bring them in with Insert › Link CAD as a background to trace, but rebuild the symbols as families instead of inserting blocks into the model.
When the symbols do not show up
| What you see | Why | What to do |
|---|---|---|
| The No Tag Loaded box appears when you click | That category has no tag family in the project | Answer Yes to load one, or load it first through Insert › Load Autodesk Family |
| The label reads a question mark | The parameter the label reads is empty on the object | Fill that parameter in Properties and click Apply, or point the label at another parameter |
| Tag All skips the architectural fixtures | Include elements from linked files was not ticked | Reopen Tag All, tick the box and run it again |
| Label text is far too large or too small | Annotation text is sized against the view scale | Change View Scale, or change the text size in the tag type properties |
| Legend symbols are smaller than the wording | The legend view scale is too small for the equipment size | Set the legend to 1:10 or 1:20 |
| Labels vanish on the printed sheet | The annotation category is switched off in Visibility/Graphics | Turn it back on in the Annotation Categories tab |
Three things people still say about MEP tags
| What people say | What Revit 2027 does |
|---|---|
| A Revit symbol is a block like in CAD | The equipment symbol is linework inside the family and travels with the object; only annotation symbols are separate 2D families |
| Labels are just text, delete them to lighten the sheet | A label reads a parameter; deleting it removes the cross-check against the schedule |
| The leader tick box is on the Options Bar | In 2027 Leader Line, Leader Start, Leader End, Orientation and Angle all sit on the Modify Tag contextual tab |
Frequently asked questions
How is a tag different from typed text?
A tag reads a parameter of the object, so it follows the model. Text typed with the Text command stays put, keeps the old number after the model changes, and that is where drawings and schedules start to disagree.
Where do symbols come from when the family library is not installed?
Three sources: your office template, the online content through Insert › Load Autodesk Family, and families you draw yourself in the Family Editor. A Vietnamese drawing set usually needs all three.
Is there a Vietnamese standard for electrical drawing symbols?
Yes. TCVN 7922:2008, Graphical symbols for diagrams, is in force and is identical to IEC 60617:2002. The older TCVN 185:1986 has been withdrawn and should no longer be printed in a title block.
Can one legend serve several sheets?
Yes. A legend is the only view type that can be placed on more than one sheet without being duplicated, so the symbol table is built once for the whole set.