# Can you measure current without voltage on X20AP3xxx modules?

**URL:** <https://community.br-automation.com/t/can-you-measure-current-without-voltage-on-x20ap3xxx-modules/10578>\
**Category:** How-To & Wikis\
**Tags:** x20, fieldbus, plc\
**Created:** [March 20, 2026, 1:14pm UTC](https://community.br-automation.com/t/can-you-measure-current-without-voltage-on-x20ap3xxx-modules/10578 "2026-03-20T13:14:26Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![tomas.miculka](https://avatars.discourse-cdn.com/v4/letter/t/FF8800/32.png) [@tomas.miculka](https://community.br-automation.com/u/tomas.miculka)\
**Post date:** [March 20, 2026, 1:14pm UTC](https://community.br-automation.com/t/can-you-measure-current-without-voltage-on-x20ap3xxx-modules/10578/1 "2026-03-20T13:14:26Z")

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## Question

Is it possible to measure the current consumption of a phase using the **X20AP3xxx** module without having the phase voltage connected?

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## 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.

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## 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:

- **Current path** : External current transformer → Measurement shunts → Anti-aliasing filter → A/D converter

- **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 |

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## Reference

- B&R Online Help — X20(c)AP31xx Technical Data:

- [X20AP3111, X20AP3121, X20AP3131](https://help.br-automation.com/#/en/6/hardware/x20ap31x1/technische_daten_x20ap31x1.html)

- [X20AP3122, X20AP3132](https://help.br-automation.com/#/en/6/hardware/x20ap31x1/technische_daten_x20ap31x2.html)

- [Typical connection examples](https://help.br-automation.com/#/en/6/hardware/x20ap31x1/anschlussbeispiele.html)

> **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.

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<div class="post-metadata">

**Author:** ![kovarj](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/kovarj/32/537_2.png) [@kovarj](https://community.br-automation.com/u/kovarj)\
**Post date:** [March 22, 2026, 10:34am UTC](https://community.br-automation.com/t/can-you-measure-current-without-voltage-on-x20ap3xxx-modules/10578/2 "2026-03-22T10:34:48Z")

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cool, thanks for sharing 🙂