LV switchgear FAT: what to check before the panel leaves the factory

By Eng. Mannan Maqsood, Electrical EngineerPublished 11 November 20264 min read

A defect found at the factory costs a few hours of a panel builder's time. The same defect found after the board is installed, cabled and energised can cost weeks: a shutdown, a new part shipped from overseas, and a second witness test. The factory acceptance test (FAT) is the last cheap moment to catch problems. Yet many FATs are rushed, with the visitors looking at the paint and the nameplate and signing a pre-printed form. This article sets out what to check, in an order that works on the day.

Before you travel

• Approved documents: the latest approved GA drawing, SLD, schematic and wiring diagrams, and the approved material submittal with brand and model numbers. Without approved documents you cannot say the panel is right or wrong.
• The FAT procedure: ask for it in advance and agree it. It should list the routine verification items of IEC 61439-1, the functional tests, and the test equipment with calibration certificates.
• Design verification evidence: confirm you have the original manufacturer's design verification reports for the system, covering the ratings on your drawings. This is reviewed before the FAT, not during it. See our article on IEC 61439 vs IEC 60439.
• Ready status: ask the panel builder to confirm the board is fully complete and internally tested. A half-built board is not ready for a FAT.

1. Compare the board with the drawings

Walk the board section by section with the approved GA and SLD in hand.

• Section arrangement, dimensions, cable entry (top or bottom) and gland plates as approved
• Incomer type, rating, poles, breaking capacity and trip unit as approved
• Each outgoing device: rating, poles, kA, trip unit and accessories (shunt trip, auxiliary contacts, motor operator)
• CT ratios, accuracy class and burden; meters and multifunction meter models
• Busbar material and size, neutral size, and earth bar size
• Spare ways and equipped spares as specified
• Form of separation as specified, with barriers actually fitted

Mark every difference on the drawing. Small substitutions, such as a different meter model or an MCCB from another range, need an approved deviation, not a verbal agreement at the FAT.

2. Routine verification to IEC 61439-1

These are the checks the standard requires on every assembly. Witness them, or witness a sample and review the records for the rest.

• Degree of protection: doors, covers, shrouds and gland plates fitted; no open holes; IP rating consistent with the nameplate.
• Clearances and creepage: visual check at busbar joints, droppers and terminals, and measurement where it looks tight.
• Protection against electric shock and protective circuit integrity: continuity of the protective circuit between exposed metal parts and the main earth bar, including doors with earth straps.
• Incorporation of components: devices installed as the manufacturer instructs, with the right clearances and accessories.
• Internal connections: busbar joints and power connections tightened to the specified torque and marked. Check a sample with a calibrated torque wrench.
• Terminals for external conductors: suitable for the size and number of cables on the cable schedule, with room to make off the cables.
• Mechanical operation: doors, racking mechanisms, interlocks, handles and padlocking work smoothly.
• Dielectric test: power-frequency withstand test at the voltage required by the standard, with electronic devices disconnected as the procedure states, and insulation resistance recorded.
• Wiring, operational performance and function: control wiring checked against the schematic, then functional tests.

3. Functional tests

• Breaker operation: open, close and trip each ACB and motorised MCCB electrically and mechanically.
• Interlocks: mechanical and electrical interlocks between incomers, bus couplers and generator incomers. Try to close what should not close.
• ATS or changeover logic: simulate mains failure, generator available, mains return, and the time delays. Check the sequence against the approved logic diagram.
• Protection: secondary injection of relays or trip units where specified; confirm that settings are as per the approved coordination study, not factory defaults.
• Indication and metering: lamps, alarms and meter readings with simulated signals; BMS interface signals at the terminal block.
• Power factor correction: step switching from the controller, detuning reactors fitted if specified, discharge resistors present.

4. Labels, finish and documents

• Nameplate showing the manufacturer, type designation, serial number, standard, Ue, InA, Icw and duration, IP, form, and the date
• Device labels matching the SLD and DB schedules, in the specified language and material
• Ferrules on control wiring matching the wiring diagrams
• Paint finish and colour; sample thickness readings if specified
• Routine verification report for this serial number, test certificates for devices and CTs, and the as-built drawing set

The defects that turn up most often

1. Trip unit settings left at factory default instead of the coordination study values
2. Busbar joints without torque marks, or a few bolts clearly loose
3. Interlock that can be defeated by operating in a different order
4. Earth straps missing on doors carrying electrical equipment
5. Cable terminals too small for the cable sizes on the cable schedule
6. Different meter or relay model from the approved submittal
7. Form of separation barriers missing in one section
8. Labels wrong or missing, especially on spare ways

Close it properly

End the FAT with a written snag list that lists each item, the agreed action and who will verify it, and record whether the board is accepted, accepted subject to snags, or rejected. Do not sign "accepted" with open items that affect safety or ratings. The LV Switchgear Verification & Assembly Lab walks through the routine verification and builds a FAT certificate, and the Switchgear & DB Checklist Suite gives printable checklists. The acceptance values for your project always come from the approved specification, the standard and the manufacturer.

Disclaimer. This article is general technical information for education only. It is not professional engineering, design, legal or safety advice for any specific project, and it does not replace the judgement of a qualified, registered engineer who has reviewed the actual installation. Worked examples and figures are illustrative and do not describe any identified project, client or site. Codes, authority requirements and product data change, so confirm every value against the edition that applies to your project, the authority having jurisdiction and the manufacturer's data. Any testing or work on live systems must be carried out only by competent, authorised people under the approved procedure. The views are the author's own and do not represent any employer, client or authority. To the extent permitted by law, the author, the editor and MEPVirtual accept no liability for any loss, damage or injury arising from the use of, or reliance on, this content. See the full disclaimer or report a correction.