What J means on a P&ID.
You can go a whole career without seeing a J tag on a process P&ID. Power gets measured plenty in industrial plants, but the measurement usually lands on the electrical single-line as a voltage-times-current calculation rather than a dedicated power meter. The exception is large rotating equipment, compressors, pumps, mills where shaft power is the controlled variable for surge protection or load balancing.
Also stands for.
- Scan, rare specifications
Common second letters.
| Tag | Meaning |
|---|---|
| JT | Transmitter, JT. Power transmitter, kW or VA |
| JI | Indicator, JI |
Example tags.
| Tag | Meaning |
|---|---|
| JT-605 | Power transmitter, often a motor kW meter |
Typical placement.
On large rotating equipment, compressors, pumps, mills where power consumption is a process variable. Less common than the matching electrical tags, E-voltage, I-current.
Common questions
What does the ISA 5.1 first letter J stand for?
In ISA 5.1, the first letter J stands for Power. It can also stand for Scan, rare specifications.
How is letter J typically used on a P&ID?
On large rotating equipment, compressors, pumps, mills where power consumption is a process variable. Less common than the matching electrical tags, E-voltage, I-current.
What second letters commonly follow J in ISA 5.1 tags?
Common combinations include JT (Transmitter, JT. Power transmitter, kW or VA), JI (Indicator, JI).
What are example ISA 5.1 tags starting with J?
JT-605 (Power transmitter, often a motor kW meter).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.