An engineering firm sells decisions, not custom control panels. It studies the load, sizes the assemblies, and issues the drawings someone else builds from. That work is the part you cannot buy from a catalogue.
This guide covers what you actually buy. It covers the document set and the handover to control panel fabrication. It also covers the fee models and how to brief a firm in one page.
Key Takeaways
- You are buying decisions, not cabinets. The firm fixes ratings, routes and interfaces before any steel is cut.
- Six documents come first. The load schedule and the single line diagram decide nearly everything that follows.
- The seam must be written down. Design authority and the build are two jobs, and they have two owners.
- An open specification has three bidders. If only one factory can quote it, the design is closed.
- Free design is never free. A drawing given away with an order belongs to the seller, not to you.
What an engineering firm actually sells
You are buying a decision set rather than a product. The firm fixes the ratings, the routes and the interfaces before anyone builds.
That is why a serious firm asks for your load list first. It cannot size an incomer, a busbar or a clearance without it.
A good control panel design company charges for the questions it asks. It does not charge for the drawings it formats.
So ask what will be decided by the end of stage one. If nothing is decided, you bought formatting. A custom control panel design is a long list of decisions, not a template.
The document set that must exist before fabrication starts
Six documents should exist before a builder cuts metal. Ask for all six, and ask who signs each one.
The load schedule fixes the ratings. The single line diagram fixes the incomer and its protection. The panel layout fixes the footprint and the cable space.
The device schedule fixes what sits inside. A discrimination study fixes which device trips first and when. A power quality study decides whether you need a power factor correction panel at all.
Together those documents control the electrical panel fabrication cost. Change one of them late and the factory rebuilds something.
| Document | What it freezes | Who signs it |
|---|---|---|
| Load schedule | Motor ratings, duties and quantities | Consultant |
| Single line diagram | Incomer, busbar rating and protection | Consultant |
| Panel layout | Footprint, clearances and cable space | Shared |
| Device schedule | Breakers, relays and terminal ratings | Shared |
| Discrimination study | Which device trips first, and when | Consultant |
| Power quality study | Harmonics, filtering and correction | Consultant |
Who signs the drawing and who cuts the steel
The seam between design and build has to be written down. On most projects it is the device schedule.
Above that line the consulting firm decides. Below it a control panel builder works to the issued drawings.
Move the seam and the price moves with it. A builder who also designs has little reason to keep your options open.
Four things to fix before the order is released
Ask the firm to name the seam in writing. Then the control panel builder prices below it, and electrical control panel fabrication stops being a guess.
Everything below the seam is built and verified to IEC 61439. That standard is what the works test record refers to.
An open specification is not tied to one maker
Write the specification around ratings and interfaces, not around one catalogue. Otherwise you own a spare parts problem for twenty years.
This is where many tenders go wrong. A consultant who rewords a single maker's datasheet has not designed anything.
The test is short. Send the document set to three separate electrical panel manufacturers. If only one of them can quote, the design is closed.
Device lists drift this way. A specification that names the ratings lives longer than one that names a part number. That holds for industrial electrical panels of every size.
Most custom control panels are built once. The specification is the document that has to survive for the whole life of the plant.
The breakers the schedule names
Every circuit breaker above sits where the device schedule puts it.
The wiring duct below carries the control wiring into the terminals.
The medium voltage edge of the scope
Most design work sits below one kilovolt. Above roughly one kilovolt the shape of the assembly changes.
The breaker moves into a metal enclosure. Clearances widen and the test regime changes. So say which side of the line the job belongs to.
A 400 V board and an 11 kV lineup are not the same job. They need different metal enclosed switchgear and different specialists.
Copper and bushings, sized for the fault level
The copper busbars and bushings above belong to the medium voltage side.
Below one kilovolt the same connection looks completely different.
Design work on a plant that is already running
Retrofit design is a different job. The plant keeps running, and the outage window is measured in hours.
So the first deliverable is a survey rather than a drawing. Photograph the switch room and measure every spare way.
Humidity and dust decide the enclosure as much as the load does. In a humid textile mill the cabinet rating carries real weight.
Measure the footprint of each existing industrial electrical cabinet first. A replacement that will not fit the room is not a design.
Then ask for a phased plan. A custom control panel manufacturer can build in stages while you keep producing.
How consulting engineers are paid
Fees come in three shapes. Each one changes who owns the drawing at the end.
| Fee model | How it works | Watch for |
|---|---|---|
| Percentage of equipment value | A share of the ordered value | The fee rises when the equipment does |
| Lump sum per deliverable | A fixed price for a named document set | Safe only when the scope is closed |
| Time and materials | Charged by the engineer day | Open ended without a written ceiling |
Be careful with free design bundled into a supply order. That drawing is written for one factory's stock.
A free drawing is rarely free. It is a closed specification wearing a friendly hat.
A firm with a working ISO 9001 system can show you its own checking routine. Ask to see it before you sign.
How to brief a firm in one page
A short brief returns a usable proposal. Long documents usually return a template.
Send four things together. What exists now. What has to be decided. The one constraint you cannot move. And the date you need the drawings.
Add the load list and any existing drawings, even rough ones. Control panel designers can work from a marked photograph when nothing else exists.
Say who will build the custom industrial control panels. It changes the drawing conventions. It also changes how much detail the firm has to issue.
The result should be one page of scope and one page of price. A firm that sends forty pages has not read your brief.
Frequently asked questions
What does an engineering firm actually deliver?
How is consulting work on industrial electrical systems priced?
Who owns the drawings at the end of the project?
Can a factory do the design as well as the build?
How long does the design stage take?
What if the plant has no as-built drawings?
Do I always need a discrimination study?
What is the difference between a specification and a datasheet?
Final thoughts
The document set is the product. Everything built later follows it, so the decisions matter more than the drawing template.
Brief one firm with one page and a load list. Then compare custom control panels on the decisions rather than on the paperwork.
Industrial load keeps growing. The IEA tracks how much of it lands on networks sized for less.
Send the load list, whatever drawings exist, and the outage windows you can accept. Giantele engineers return a marked layout, a device schedule and a written scope for each stage.
Need the design split from the build in writing?
Send the load list, the existing drawings and the outage windows you can accept. Giantele engineers return a marked layout, a device schedule and a written scope for each stage.
