Question
Is it possible to measure the current consumption of a phase using the X20AP3xxx module without having the phase voltage connected?
Answer
Yes, it is possible. The current inputs and voltage inputs on the X20AP3xxx modules are independent of each other. You can measure current (via current transformers) even when the corresponding phase voltage is not connected to the module.
Technical Background
The X20(c)AP31xx family are 3-phase power and energy metering modules designed for use with current transformers. Their internal architecture separates the current measurement path from the voltage measurement path:
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Current path: External current transformer → Measurement shunts → Anti-aliasing filter → A/D converter
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Voltage path: Voltage inputs → Overvoltage protection → Anti-aliasing filter → A/D converter
Because these paths are separate, the current measurement circuitry operates independently of the voltage inputs. This is also reflected in the hardware design of the X20AP31x2 variants, where the neutral terminal (U N) is explicitly marked as “Not connected” in the circuit diagram — confirming that current measurement does not depend on a voltage reference being present.
| Model | Measurement type | Neutral (U N) required? |
|---|---|---|
| AP3111, AP3121, AP3131 | Current measurement | Optional (can be left unconnected) |
| AP3122, AP3132 (AP31x2) | Current measurement | Not connected by design |
| AP3161, AP3171 | Voltage measurement | Required |
Reference
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B&R Online Help — X20(c)AP31xx Technical Data:
Note for AP31x2 users: Modules X20AP31x2 are not permitted to be used with network configurations that require grounding (configurations B, D, and F) due to the lack of grounding on the neutral terminal.
