Marshalling Box in HV Switchyard of Power Plant

If you are a trainee on a site, then all the drawings of equipment, terminal boxes and cabling are on site - and so is the equipment to examine. Drawings of another site will not help so much.

Find out where the drawings are stored. Ask someone there where the drawing lists are. They will have knowledge of what lists/ drawing sets everything is split into and what they are called, so tell them you need drawings to trace wiring from VTs/CTs to protection relays or ? The lists are probably computer files and drawings may be on-screen & available to print.

There will be a master "list of lists". There will likely be several sub-contractors and a list each. There will be cabling diagrams listed. There will be drawings for trays or trenches the cables run-in. Lists "cable by cable" and routing & termination lists or diagrams. Start with "Single Line Drawings", "General Arrangements" or "site plan". There is probably a "master layout/scheme" for site cabling to show run positions and interfaces. Get a copy of lists and drawings, if you can.

There are contractual or timescale reasons for marshalling. Even if there is one main contractor it is very unlikely every kind of equipment comes from one factory/design point.

When contracts are placed, it is unlikely many details have been designed and drawn. Particularly, the locations of switchgear, busbars, supports will not be available until the design is done - consequently, CT and VT locations are unknown.

I once had a monitor contractor who would not release any drawings until everything was done even though we said we wanted same plugs & pin-outs as last time. The panel builder got very annoyed he could not finish and ship job until information came. Delays can cost a lot of money!

Although it seems that VT/CT could be wired direct to remote relays and this minimises joints, activities cannot be done at the same time "in parallel" if one contractor has to wait until another has finalised every detail. Marshalling allows an interface point to be fixed in position and content earlier in design and a clear contractual responsibility.

When fault finding or measuring within the substation it would be most time-consuming to move from one VT/CT etc box to another with High Tension hazards to avoid and to have multiple covers off. If there is rain, snow or dust, it as more practical to have one (or minimum number) tent or walk-in marshalling cubicle.

When a sub-contact is actually placed, one of the first questions will be "where are the mechanical and electrical interface points - if you do not know, when will they be provided (and the termination details)?".

Finding out where something is and how it is connected is often the most time consuming part of a job - welcome to the club.