Can a Siemens AFDiSD or AFD Be Powered Without an FDC?

No separate auxiliary supply input is documented for the Siemens AFDiSD 6ES7655-5DX60-1BB0: its supply is via the PROFIBUS PA fieldbus. To check power without PA instruments on the spurs, use a correctly designed and energized PA segment with the appropriate coupler and verify supply at the distributor. That confirms only a limited power-up condition, not communication or full device health. Identify the exact AFD model before applying its specifications.

Power Source for AFDiSD and AFD

The Siemens DP/PA coupler and active field-distributor manual specifies fieldbus power for the AFDiSD (6ES7655-5DX60-1BB0) and AFD4 variants it documents; the AFDiSD has a 16–32 V DC permissible range and is powered via the fieldbus. It is not specified with a separate auxiliary-power input for a standalone bench test. Without a suitable energized PA segment/coupler such as the FDC 157 arrangement, do not apply an improvised supply to its fieldbus terminals.

What a Power-Up Check Can Confirm

With the product wired into a correctly designed and energized PROFIBUS PA segment, the distributor can receive its specified fieldbus supply even if no PA field devices are attached to its spur lines. This can establish that supply is present, but does not by itself prove full communications, diagnostic or repeater functionality. The exact test and segment configuration must follow the model's manual and plant requirements.

Safe Preparation

Identify the full order number and hardware version; “AFD” covers different models and connection arrangements.
Confirm whether the device is AFDiSD 6ES7655-5DX60-1BB0 or a particular AFD4/AFD8 variant and use its corresponding Siemens technical data.
Use the specified fieldbus supply path and a properly configured FDC/PA segment. Check segment voltage, available current, polarity, terminations and hazardous-area constraints against the system design.
Connect only with the segment de-energized where required by the manual and hazardous-area rules. For AFDiSD, observe the manual's enclosure/zone precautions; it prohibits opening the IP30 cover during operation in Zone 1.
Energize the designed segment and observe only the checks specified for the exact device. Do not infer device health from a power LED alone.

Expected Results and Limits

For AFDiSD, Siemens lists supply via fieldbus, with a permissible 16–32 V DC range. The manual's electrical specifications do not constitute a complete standalone acceptance test. Diagnostics, PA communication and connected field-device operation require the relevant configured system. A no-load test should not be represented as proof of fieldbus function.

Verification

Check the actual part number, confirm the PA segment supply is within the device specification at its connection point, and compare device indications/diagnostics with the matching manual. If the objective is only to verify that it powers up, record that limited observation separately from communications or device-function testing.

Limitations and Operational Precautions

The ticket does not identify the exact AFD model; electrical data and features differ among AFD variants. Do not connect an external DC supply directly to PA bus terminals unless a Siemens document for the exact model explicitly specifies that test method. Follow hazardous-area, isolation and plant change-control rules. The FDC itself has a separate supply connection; that does not imply the active field distributor has an auxiliary supply input.

Engineer FAQ

Does AFDiSD have a separate auxiliary supply input? Siemens documents its supply as via fieldbus, not a separate auxiliary input.

Can I power the AFDiSD without PA field devices attached? A correctly supplied PA segment can energize the distributor with unused spurs, but that limited check does not prove communications or complete functionality.

Can a bench DC supply be connected directly to the PA terminals? The cited manual does not specify this as a standalone test; do not improvise it.

What voltage applies to AFDiSD 6ES7655-5DX60-1BB0? Siemens lists 16–32 V DC permissible via fieldbus.

Does an illuminated indicator prove the PA network is healthy? No. Check communication and diagnostics using the configured system and model-specific instructions.

Technical References

Siemens, DP/PA coupler, DP/PA link, Y-link and active field distributors, Operating Instructions, 12/2021, A5E37478314-AA, §12.6 (AFDiSD technical specifications) and §12.7 (AFD4 specifications): https://cache.industry.siemens.com/dl/files/389/109805389/att_1089879/v1/dppa_coupler_afdis_dppa_link_y_link_manual_en-US.pdf?download=true