Topic
Panel & Electrical
Control panel design and build: layout, thermal sizing, cable segregation and noise, grounding and bonding, and enclosure ratings.
7 articles
Free control panel design software: electrical CAD compared
QElectroTech is the most complete free option: GPL-licensed, on Windows, macOS and Linux, with cross references, automatic conductor numbering and CSV export of the parts and wire lists. ProfiCAD's free Home licence is for hobby use and stops at three pages. SEE Electrical offers a 30-day trial. LADX CAD is free browser drafting with DXF export.
7 min readControl panel wire colour codes: NFPA 79 vs IEC 60204-1
Under NFPA 79 (2024), power wiring is black, AC control red, DC control blue, and anything still live with the main disconnect off is orange, with a blue stripe for DC. The equipment grounding conductor is green, with or without yellow stripes. IEC 60204-1 requires green-and-yellow for protective earth and blue for neutral, and recommends black, red, blue and orange for the rest.
8 min readLaying out a control panel that can be worked on
Segregate by voltage and by signal type, keeping mains, 24 volt control, analogue and network in separate trunking runs. Put heat producing items high and heat sensitive items low. Leave room for a hand and a screwdriver at every terminal, and leave spare space, because every panel gets modified. Label everything to match the drawings, since the drawing is what somebody will have at two in the morning.
8 min readSizing an enclosure for the heat inside it
Add up the heat dissipated by everything inside, usually a few percent of throughput for drives and power supplies, and compare it with what the enclosure dissipates naturally, roughly 5.5 watts per square metre of free surface per degree of temperature difference. If the internal temperature would exceed the most sensitive component's limit at the site's maximum ambient, you need cooling, and which type depends on whether outside air is clean enough to bring in.
7 min readElectrical noise: where it comes from and how to stop it
Separate signal cable from power and motor cable, ideally by at least 100 mm and in different trunking, crossing at right angles where they must cross. Use screened cable for analogue and network, and terminate the screen over its full circumference at the panel entry rather than as a pigtail. Where separation is impossible, an isolated input or a signal isolator solves it properly.
7 min readEarthing and bonding, and the difference between them
Bonding connects conductive parts together so they sit at the same potential, which is what makes a touched surface safe. Earthing connects that bonded system to the general mass of earth, which gives fault current a path and lets protective devices operate. Functional earth is a third thing entirely: a reference for signals, and it should not share a path with fault current.
7 min readIP ratings and NEMA types, and which one to specify
IP65 means dust tight, the 6, and protected against low pressure water jets from any direction, the 5. The first digit is solids from 0 to 6, the second is water from 0 to 9K. NEMA types cover similar ground and add corrosion and ice requirements that IP does not, so a NEMA type can be converted to an approximate IP rating but not the reverse.
6 min read