J - Power
Reference for the ISA 5.1 first letter J. 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.
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Also stands for.
- Scan, rare specifications
Common second letters.
Transmitter, JT. Power transmitter, kW or VA
Indicator, JI
Example tags.
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.