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Main Distribution Board MDB Testing & Commissioning Procedure

Upon completion of the LV Distribution Board installation including proper terminations into each breaker, the same shall be offered up for inspection from consultants. Earth fault loop impedance test & earth leakage test for LV Distribution Board shall be done & recorded in prescribed format.

There are 3 cases to be considered.


Case 1 is ONLY interconnecting cable between Upstream and Downstream Panels, e.g. between Transformers and MDB’s.

i) Physically inspect entire cable length for any tell tale signs like skirmish (peeled off cable outer sheath). Arrange for repair and resume immediately.

ii) Inspect and confirm all cable terminations (cables to Breaker/Busbars/Terminal Blocks) are in order including phase sequence/rotation and insulation sleeve

iii) Thoroughly clean Panel/Cabinet just before energisation.  Conduct insulation Test with Megger set at 1000V at receiving end (Upstream breaker remains at “OFF” position).  Minimum Insulation Resistance is 20 MΩ. Rectify problem if reading obtained is below 20 MΩ

iv) Panel is ready for energisation when results for above steps (i) through (iii) are OK.  Arrange to “Turn ON” respective Feeder in Upstream Panel while keeping receiving end incoming breaker at “OFF” position.

v) Note and record instruments reading in record book.

vi) Pad Lock receiving end Panel Incoming circuit breaker in “OFF” position and return key to Administrator who will keep key inside designated Key Box (Kept inside LV Switch Room).

vii) Thoroughly clean area in front and around “energized” panel to ensure cleanliness and area free from any conducting materials.  Arrange and lay approved rubber mat around “energized” panel.

main-distribution-board MDB Testing Procedure

Case 2 is Case 1 and some outgoing feeders simultaneously.

i) Repeat steps (i) as in Case 1 for all cables (include all available outgoing feeders’ circuit for consideration).

ii) Repeat steps (ii) through (vi).

Case 3 is the remaining outgoing feeders after partial energisation from Case 2.

i) To minimize unnecessary shutdown and or deprive others the chance to access the “Upstream” panel, all work including cable laying and terminations away from “Upstream” panel have to be completed prior to application for PTW.

ii) Physically inspect each length of cable laid from “upstream” panel to each sub-system like MDBs, SMDBs, Lift and Escalator, AHUs etc. are properly terminated and free from cable skirmishes that require repair work. Once completed proceed to step (iii) to completion.

iii) Apply for Permit to Work (PTW) describing in details type of work to be performed, “extent” of electrical isolation required, place of work and expected duration (time to complete work).

iv) Confirm Administrator had Shutdown/Open Incoming circuit breaker in Upstream and downstream Panels and an appropriate “Warning Sign” displayed against these 2 circuit breakers.

v) Keep the key/s given by Administrator and repeat steps (i) through (iii) as in Case 1 until work is completed. Turn “Off” all feeder circuit breakers.

vi) Withdraw men and equipment/s from Site and return PTW (Declare Panel/Switchboard is “Complete” and No “further” Addition/Alteration is required) when you are satisfied with the work executed for “Cancellation”.

vii) Arrange a Final Inspection for “Complete” Panel/Switchboard.

viii) Arrange Permit To Run (PTR) if you need to test run down stream sub-system like AHU, FCU, Pumps etc.etc after step (v) above

Notice of testing shall be advised to consultant for their discretionary attendance and witnessing. Notice shall be advised at least 48 hours prior to the proposed inspection and testing. The installation shall be inspected for compliance with the design requirement.


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