Manufacture
Manufacture of an assembly runs in a fixed order. Each stage has to be complete and correct before the next begins, because most of what is built early becomes inaccessible later.
Design and schedules
Work starts from the electrical design: single-line diagram, schedule of outgoing ways, device selection, and the discrimination study showing that a fault on a final circuit will operate that circuit’s device and not the one upstream of it. Cable sizes and the earthing arrangement follow from the same design.
Where the client has an engineer, this is agreed with them. Where the client does not, the requirements are established from the load schedule and the supply characteristics before anything is ordered.
Enclosure preparation
Enclosures are prepared before any live-side component goes in: cut-outs for devices and instruments, gland plates drilled, mounting plates fitted, earthing studs and bonding provided. Doing this first keeps swarf out of equipment, which is a genuine cause of later faults.
Busbar and power connections
Busbars are cut, formed, insulated and supported so that they carry the rated current continuously and withstand the mechanical forces a fault current produces: forces which are considerable and which will move an inadequately supported bar. Joints are prepared and torqued to the specified figure and marked once done.
Wiring
Control and auxiliary wiring is run in trunking, sized and colour-coded to the wiring convention in use, ferruled at both ends and terminated to identified terminals. Wiring is dressed so that a door can open and close through its full travel for the life of the assembly without chafing a conductor.
Inspection and routine verification
Before an assembly leaves, it is verified. That covers a visual and mechanical inspection against the drawings, continuity of the protective circuit, insulation resistance, dielectric withstand where applicable, correct operation of switching, interlocks and indication, and a point-to-point check of the wiring against the schedule.
Results are recorded and issued with the assembly. An assembly without its test record is an assembly nobody can commission with confidence.
Delivery and installation
How an assembly gets into the building is a design question, not a delivery question. Access route, door widths, floor loading, lifting points and whether the unit must be shipped in sections are established before it is built. A finished panel that will not pass through the plant room door is a very expensive mistake.