A new machine is about to go into series production, a plant is being extended, or the drawings of a control cabinet only exist on paper. In all three cases the request sounds the same. You need a schematic, drawn by someone who does this every day.
How quickly that becomes a reliable quote and later a usable drawing set depends heavily on the first documents. This article shows what to prepare, what is handed over at the end and what drives the effort.
Which schematic do you mean?
In everyday language almost every electrical drawing is called a schematic. In electrical design it is a set of documents, each with its own purpose, prepared according to IEC 61082.
- The circuit diagram shows every device and connection of a circuit. Assembly, commissioning and troubleshooting work from it.
- The overview diagram shows the power distribution in simplified form, usually single-line.
- Terminal diagrams and cable diagrams show which cable and which core lands on which terminal.
- The layout drawing shows how the devices are arranged in the cabinet.
- The bill of materials lists every article with manufacturer and order number.
A new plant usually needs all of it. An extension often needs only parts. If your request states which documents are required, the quote will be more precise.
What do I need to have electrical schematics created?
Hardly any order starts with complete documents, and it does not have to. The more of the following points are available, the faster the quote is ready and the fewer loops the design needs.
- Functional description. What should the machine or plant do, which operating modes are there, which safety functions are planned? A specification is ideal, a few pages of text or a sketch are enough to start.
- Load list. Motors with rating and starting method, meaning direct on line, star-delta or via a drive, plus valves, heaters and sensors. Rating and voltage give the motor current, and from that the cable size, protective device and contactor for every feeder.
- Signal list. If a PLC controls the plant, a list of inputs and outputs is needed, along with the control hardware that has been specified.
- Supply. Mains voltage, earthing system and, if possible, the short-circuit power at the connection point.
- Existing documents. Old drawings, scanned or on paper, plus photos of the cabinet and the rating plates.
- Your standard. Template, article master data, designation rules and preferred manufacturers.
- System, market and deadline. Which CAE system the drawings should live on in, which market the plant is intended for and when it is needed.
The target market matters because North America applies NFPA 79 and UL 508A instead of IEC 60204-1 as used in Europe. Missing information is clarified when we review your documents, for existing plants also on site.
For a first quote, a sample drawing and the key data of the plant are usually enough.
What do I receive at the end?
A schematic as a PDF looks finished but cannot be carried forward. At the first revision at the latest, someone has to redraw it. Insist on the project data in the CAE system, meaning EPLAN, ELCAD or WSCAD. The handover usually includes these documents.
- the complete CAE project in your system environment
- circuit, overview, terminal and cable diagrams
- the layout drawing, on request as 3D control cabinet design with manufacturing data
- bill of materials and cable list generated from the project
- reference designation according to IEC 81346 or your own standard
- a PDF output for assembly, commissioning and service
How do you recognise quality? Terminal diagram, cable list and bill of materials are generated from the project at the push of a button instead of being maintained by hand. Then cross-references and article data are correct as well. Our reference designation calculator shows how a designation according to IEC 81346 is built.
A schematic is more than a drawing
Every feeder is backed by a design decision. The cable has to carry the current, the voltage drop has to stay within limits, and in the event of a fault the protective device has to disconnect in time. Motors add starting current, motor protection and the choice of contactor.
Our calculators let you estimate such values for individual circuits quickly, for example the motor feeder, the short-circuit current at the cable end or the cable length for the disconnection condition. In a plant with a hundred feeders this becomes a design task. The values are set for every feeder and entered in the drawings so that they can be traced during inspection.
What does it cost to have a schematic created?
A fixed price per page rarely fits. A page with a terminal strip takes little work, a page with a safety circuit a lot. The effort mainly depends on these points.
- Scope. The number of devices, feeders and signals.
- New or existing. A new drawing set on a good template is quicker than extending an existing one that first has to be understood. If the old drawings only exist on paper, legacy drawing digitisation comes first.
- Standard. With an existing template and maintained article data, no setup is needed. If both are missing, they are built first and are then ready for every further project.
- Repeated units. Identical assemblies are created once as a macro and then simply inserted. How that works in EPLAN is described in the article on macros and templates.
- Clear requirements. Every change after design has started costs more than the same decision made beforehand.
- Depth of output. A cable diagram with core assignment, a 3D layout or manufacturing data for wire processing extend the scope.
How an order runs with us
Since 1998 we have been handling electrical design for industrial plants and for machine and plant builders, in EPLAN, ELCAD and WSCAD and as a permanent team. An order starts with a review of your documents, for existing plants with a visit on site. We then agree designation, page structure and article data in writing. During the design you receive interim versions before a mistake can spread across many pages. At the end the project sits in your system environment.
Control cabinet building, PLC programming or commissioning can be brought in through specialised partners, and we handle the technical interface. More on this on our pages on electrical design and schematics and EPLAN design services.
Checklist for your request
- Which documents do you need, from circuit diagram to bill of materials?
- Is there a functional description and a load list?
- Does a PLC control the plant, and which hardware is specified?
- Which supply and which target market apply?
- Which old drawings, photos and rating plates are available?
- In which system and to which standard should the work be done?
- When are the drawings needed?
With these answers and a sample drawing we can give you a reliable quote.
