The short answer
Panel Layouts
A panel layout drawing shows the enclosure and its back plate to scale with every component placed, numbered to the bill of material, and dimensioned so that the builder can drill the plate and the reviewer can check the spacing, the clearances, the wireway fill, the heat, and the separation of voltage classes. It shows the door from the outside with the pilot devices, the HMI, the nameplates, and the cutouts, and the enclosure with its conduit entries, gland plates, mounting, and door swing. Conventions place the disconnect and the incoming power at the top or the hinge side, the power section separate from the control section, drives with their cooling space, the controller and I/O where signal wiring reaches them without crossing power, and the field terminal strips at the bottom edge with room to land the cables, and the drawing is checked against the component dimensions, the wire bending space, the heat calculation, and the enclosure rating before the plate is cut.
Key points
- To scale, dimensioned, and keyed to the bill of material: the layout is what the builder drills from.
- Power at the top and on the disconnect side, control in the middle, I/O and field terminals at the bottom, with wireways between.
- Separate voltage classes: power, AC control, DC control, and signal in their own wireways.
- Drives and power components need the clearances the manufacturer and the standard require, and the heat calculation proves the enclosure.
- The door is a drawing too: devices, cutouts, nameplates, and the swing.
- Check before cutting: component footprints, wire bending space, wireway fill, entries, and the enclosure rating.
What the drawing contains
- The enclosure: type and rating, outside dimensions, mounting, door swing, and the location of conduit entries, gland plates, and any vents or cooling units.
- The back plate: dimensions, mounting holes, and every component drawn to scale in its position with an item number.
- Wireways: size and route, with the fill assumption and the covers.
- Terminal strips: location, length, the strip names, and the space beside them for field cables.
- DIN rails and their lengths; ground bars and shield bars.
- The door: pilot devices, selector switches, HMI, meters, and nameplates, with cutout dimensions and legend text.
- The bill of material: item number, quantity, description, manufacturer, part number, keyed to the drawing.
- Notes: the heat calculation result, the short-circuit rating, the standard the panel is built to, and the finish.
Conventions
| Element | Convention | Reason |
|---|---|---|
| Main disconnect | On the hinge side at the top, with the operating handle on the door interlocked | The handle position and the interlock are standard requirements |
| Incoming power and power distribution | Top of the plate, near the disconnect, with the distribution block and the breakers | Shortest path for large conductors; heat rises |
| Starters, drives, and contactors | Below the distribution, in the power section, with the clearances the manufacturer states | Drives need cooling space above and below and are the warmest components |
| Control transformer and power supplies | Below or beside the power section | Transition from power to control |
| Relays and control devices | Middle of the plate | Reachable, away from the power heat |
| Controller and I/O | Middle or lower, positioned so that signal wiring reaches the cards from the terminals without crossing the power section | Noise separation |
| Terminal strips for field wiring | Bottom edge, or the side nearest the conduit entries, with space beside them | Cables enter from below; the electrician needs room |
| Wireways | Between rows, sized for the wire count at the standard fill | Power, control, and signal in separate wireways |
| Ground bar | Near the entries and the terminals, bonded to the plate and the enclosure | Short ground paths |
Space and clearance
The standards and the manufacturers set the distances: spacing between live parts of different potential and to ground by voltage, the wire bending space at terminals of a given conductor size, the clearance above and below drives and power supplies for cooling, the depth between a component and the door for the door devices, and the room in a wireway for the wires it will hold at a fill that lets them be pulled and added. The layout is drawn with actual component footprints from the manufacturer drawings, not approximations, and the reviewer measures the drawing against each requirement. A layout that packs a plate to the edge builds once and can never be modified.
Heat
Every component dissipates heat, the drives most of all, and the enclosure sheds it through its surface at a rate set by its size, material, and the ambient. The heat calculation sums the dissipation from the bill of material and compares it with what the enclosure can shed, and the layout drawing records the result and the cooling method: none, a fan and filter where the rating allows, a heat exchanger, or an air conditioner where it does not. A layout that puts a drive in a small sealed enclosure in a pump room is a layout that fails in July.
The door
The door is drawn from the outside with every device in its place: the disconnect handle, the pilot lights, the selector switches, the pushbuttons, the HMI, the meters, and the nameplate for each, with the cutout dimensions for the builder and the legend text for the engraver. Devices are arranged in the order an operator reads them, grouped by equipment, with the emergency stop where a hand finds it. The door drawing also checks depth: a door-mounted HMI and a back plate component in the same space collide when the door closes.
Checks before the plate is cut
- 1
Footprints
Every component drawn from the manufacturer dimension drawing, including terminal cover projections and the space for wiring to enter.
- 2
Spacings
Live part spacings and wire bending space per the standard, measured on the drawing.
- 3
Clearances
Drive and power supply cooling space, door device depth, and access to terminals for a screwdriver.
- 4
Wireways
Fill computed from the wire count and size; separate wireways for power, control, and signal.
- 5
Entries
Conduit entries at the right side and size for the cables, clear of internal components, with the gland plate removable.
- 6
Heat
The calculation done and the cooling method on the drawing.
- 7
Rating
The enclosure type suits the location; every device on the door carries the same rating; entries and cutouts do not defeat it.
- 8
Bill of material
Every item on the drawing is on the list, and the list matches the schematic.
Frequently asked questions
- Does the layout have to be to scale?
- Yes. The builder drills from it, the reviewer measures spacings on it, and the heat and wireway checks depend on the real sizes. A schematic is symbolic; a layout is a dimensioned drawing.
- Where should the controller go?
- Where the signal wiring from the field terminals reaches it without crossing the power section, away from the drive heat, at a height where a technician can connect a laptop and read the indicators, and with space for expansion modules. The middle of the plate on the terminal side is usual.
- Can we put a drive in the same enclosure as the controller?
- Small drives, with the clearances, a separate wireway for the motor leads, the shielded motor cable leaving through its own entry, and the heat accounted for, yes. Larger drives or several drives belong in their own enclosure beside the control panel, connected by a short shielded control cable.
- What goes in the bill of material?
- Every purchased item on the drawing: enclosure, plate, every device, every terminal, the wireways, the rails, the nameplates, with manufacturer and part number, so that the panel can be built, quoted, and repaired from the list. Consumables such as wire and labels are listed by type and quantity.
Related topics
- Component LayoutArranging a panel so it is safe to work in, cool enough to run, quiet enough for its signals, and possible to modify: power and control separation, heat, wireways, terminals, and the working space rules.
- Enclosure Heat CalculationsEstimating the temperature inside a control panel from the power its contents dissipate and the surface that carries it out, what to do when the answer is too hot, and why drives change everything.
- Enclosure SelectionChoosing the box: NEMA and UL 50 type ratings, materials for corrosive and outdoor sites, sizing for heat and wire bending space, and the details at the conduit entries and the door that decide whether the rating survives installation.
- UL 508A Industrial Control PanelsWhat the listing actually covers, what has to appear on the label, and the requirements that most often cause a panel to fail inspection.
- Wiring DiagramsThe drawing that says where every wire goes: panel wiring and interconnection diagrams, and the conventions of wire numbers, conductor colors, terminal numbers, and cable numbers that make them readable. What belongs here versus on the schematic.
- How to Calculate a Panel SCCRDetermine the short-circuit current rating of a control panel by the UL 508A Supplement SB method: list every power circuit component, find each rating, apply published series combinations and current limiting, and mark the panel with the lowest result.
Direct contact
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