In this guide 6 sections
Write the test plan from the approved drawings and the customer’s specification before the panel is finished, so every line traces back to a drawing revision. Run insulation, functional and interlock checks in a fixed order, record each reading on a numbered sheet, and keep the signed sheet with the job. Do a private dry run first.
Build the plan from the approved drawings
Start with the revision of the general arrangement and schematic that the customer approved, and check the revision letter on every sheet before copying a line. An older drawing tests the wrong panel.
List each incomer, feeder, motor starter and control circuit as a test line, with expected results beside it, such as a relay picking up or a lamp lighting. Give every line a number.
Agree the plan with the customer before the panel reaches the test bay, sending it as a PDF and asking for comments on any line they want witnessed. Surprises on test day cost hours. Surprises in the plan cost an email. Choose the email.
- Drawing revision and date
- Customer specification clauses that call for a witnessed test
- Rated voltage, short circuit rating and enclosure rating
- Deviations the customer already agreed in writing
Order the checks so one result protects the next
Begin with a visual and torque check of busbar joints, terminals and earthing, because a loose joint shows up later as a false fault that wastes an afternoon. Torque them to the marked value.
Run the insulation resistance test before any live functional test, since a megger reading across phases and to earth takes minutes and prevents a burnt control transformer. Beside each reading, record the instrument, its serial number and its calibration date, so an auditor can trace the megger to a certificate.
Functional checks follow: energise the control circuits from a test supply, run each starter, and operate every pushbutton, selector and emergency stop on the door. Withstand testing comes last, if specified. Keep the same order for every panel of one type, because repetition speeds the technician, makes records comparable between jobs and exposes the odd panel that behaves differently.
- Visual, wiring and torque check
- Insulation resistance, phase to phase and to earth
- Control circuit and functional operation
- Protection relay settings and trip tests
- Withstand test if specified
Test every interlock as a sequence, not a single push
Interlocks fail in combinations. A key interlock may work alone yet fail when the earth switch is closed and the door is open, so write it as a sequence of states.
Try the forbidden move too. Attempt to close a breaker with its mating switch open, then try to open a panel door while the isolator is on. A passed interlock blocks the wrong move.
Note any bypass link used in commissioning. Remove it before the customer arrives.
- Door and isolator interlocks
- Breaker and earth switch key interlocks
- Changeover and bus coupler interlocks
- Emergency stop and trip circuit reset
Record readings where the witness can see them
Print the sheet with a blank for the reading, the pass or fail box, the tester’s initials and a space for the witness. Fill it as you test. A witness trusts a pen mark made in front of them, and never trusts a page typed up from memory the next morning.
Hold a dry run a day earlier with nobody watching, so the missing cable label and the flat test set battery appear before the customer does. The customer then sees a clean run.
Close out with sign offs stored against the job
Both parties sign the sheet. Name an owner and a due date for every open point, then list each as a punch item so that no panel leaves with an unlisted remark.
Scan the signed sheet and file it against the job number with the drawing revision, serial numbers and photographs, so a site query next year takes one search. Start with the sheet template this week.
The file is part of the product. Many customers ask for the dossier with the panel, and a tidy one speaks for your quality, while missing sheets are the usual complaint.
Panel FAT witness sheet
A two page sheet. Page one holds the job number, drawing revision, panel tag, instrument serial numbers, calibration dates and the name of the customer’s witness. Page two runs down the numbered tests, with boxes for the check, expected result, measured reading, pass or fail, tester initials and witness initials. The foot carries a punch list of open points, each with an owner and a due date, ready to hand to the customer.
Open a blank worksheet to printQuestions owners ask
Who should be present at a panel FAT?
Your quality lead and the test technician attend, plus the customer or an inspector they name, with the design engineer waiting nearby for drawing questions. Too many people slow the run.
Do we need a dry run before the customer arrives?
Yes. A private run finds wiring slips, missing labels and unset relays, and it tells you how long the real test will take on the day.
What do we do when a check fails in front of the witness?
Record the failure on the sheet, fix the cause, then repeat the failed check and every neighbouring check it could have disturbed. Never overwrite the first reading. Both entries stay.
How long should the records be kept?
Keep them through the warranty period and any contract term, whichever ends later, and longer still for switchboards that customers expect to extend with new feeders. Old sheets save arguments.