What N means on a P&ID.
Of all the user's-choice letters, N is the one with the least convergence across operating companies. There's no convention to learn. If you see N on a drawing, the legend defines it for that project and that project only. Don't carry a meaning across job boundaries. That's how you ship a misclassified loop on a new project.
Also stands for.
- No standard assignment
Common second letters.
| Tag | Meaning |
|---|---|
| NT | Transmitter, whatever the operating company has assigned N to mean |
Example tags.
| Tag | Meaning |
|---|---|
| NT-105 | Whatever N has been defined to mean on the project legend |
Typical placement.
Wherever the project legend allows.
Common questions
What does the ISA 5.1 first letter N stand for?
In ISA 5.1, the first letter N stands for User's choice. It can also stand for No standard assignment.
How is letter N typically used on a P&ID?
Wherever the project legend allows.
What second letters commonly follow N in ISA 5.1 tags?
Common combinations include NT (Transmitter, whatever the operating company has assigned N to mean).
What are example ISA 5.1 tags starting with N?
NT-105 (Whatever N has been defined to mean on the project legend).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.