E - Voltage
Reference for the ISA 5.1 first letter E. Most voltage measurements never make it onto a process P&ID. They live on the electrical single-line drawing set instead. The E tags you do find tend to be MCC bus voltages or generator outputs that the BPCS pulls in for operator indication. Treat E tags as imports from the electrical scope rather than instruments the I&C team designs.
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Also stands for.
- Electrical, any electrical measurement
Common second letters.
Transmitter, ET. Voltage transmitter
Indicator, EI. Voltmeter
Alarm high, EAH. High voltage alarm
Example tags.
Voltage transmitter, loop 501
Voltage indicator, panel meter
Typical placement.
On electrical systems that interface with the process control system. Motor control center signals, generator output monitoring, electrical room metering brought into the BPCS for indication. E-prefix tags are not common on process P&IDs but appear on integrated drawings that overlay process and electrical scope.