Electrical & Electronics

Where it pays off

A panel will still be standing in the same place ten years from now, but only an up-to-date schematic tells you what is inside it. Most of the work on the electrical side comes from those two things drifting apart: a change is made in the field, the drawing stays as it was, and the gap becomes the problem of whoever is chasing a fault later.

The work we see most often:

• New panel design and build. Starting from the load list and producing the schematics, layout, bill of materials and test protocol together.
• Revising an existing panel. Adding devices to a line, swapping a drive or renewing the control layer while keeping the enclosure and field wiring in place.
• Documenting an undocumented panel. Measuring and tracing on site to put the real situation on paper — later modifications usually live only in the wiring.
• Motor starter sections and drive panels. Layouts that account for the heat, harmonic and EMC load of soft starters, VFDs and servo drives.
• Board design. Low-volume electronics for interfaces no off-the-shelf product covers: signal conditioning, level conversion, custom I/O and adapter boards.

From drawing to panel

We start with the load list: which consumer, how many kW, what duty cycle, how many of them run at once. Guess the diversity factor and the main breaker ends up either needlessly oversized or a device that trips through the summer.

Cable sizing and protection selection sit on top of that. Conductor size is set as much by voltage drop and installation conditions as by current-carrying capacity; ignore the derating factor for ten cables sharing a tray and the design is right on paper and hot in the field. On the protection side, two calculations are done separately: prospective short-circuit current (for breaking capacity) and discrimination (selectivity). A fault on one motor section must not trip the incoming breaker, otherwise a single failed winding stops the whole plant.

Layout is judged by maintainability: frequently replaced devices within reach, terminal rows oriented toward the cable entry, instruments and indicators on the door. Layout comes with a thermal calculation. Internal temperature follows from the power losses of the installed devices and the enclosure’s dissipating surface; the result tells you whether a fan, a cooling unit or a larger enclosure is required. The IP rating is part of that same calculation — an IP54 and an IP66 panel do not behave the same thermally, because the second cannot ventilate naturally.

Verification after build follows the steps IEC 61439 asks for: visual inspection, wiring and functional checks, insulation resistance measurement, continuity of the protective circuit. The record stays in the panel’s handover file — leaving the evidence behind is part of the job.

EMC and functional safety

In any panel containing a drive, EMC is a design decision rather than a filter fitted later. A drive output produces high-frequency switching noise, and that noise is managed with a shielded motor cable, a 360-degree shield termination at both ends, separated routes for power and signal cables, and a deliberate earthing scheme. Bonding the shield only at the panel end is a common habit; the typical result is analogue signal ripple whose source nobody can find.

Functional safety follows a fixed order: risk assessment, determination of the required performance level (PL a to e under ISO 13849-1, SIL under IEC 62061), then building the circuit to match. Emergency stop, guard door interlocks and light curtains run through a safety relay or a safety PLC; the category chosen decides whether dual channels and fault diagnostics are required. IEC 60204-1 provides the general framework for the electrical equipment of machines; CE marking only means something once the technical file, risk assessment and declaration of conformity stand together.

What we watch for

Field changes go into the drawing the same day. A terminal number changed during commissioning that is not recorded that day will probably never be recorded, and six months later the panel is undocumented again.

Tagging speaks the same language as the drawings. Cable markers, terminal numbers, device codes and schematic references all come from one system. That, more than anything, sets how long fault-finding takes.

The thermal budget is not a closed calculation. A drive added to a panel later quietly breaks the heat balance, and the effect shows up on the first hot days. When we leave spare mounting space we leave spare cooling capacity with it.

Spare part availability is a selection criterion. A brand the maintenance team cannot source is the wrong choice, however good its datasheet looks.

How this connects to the other areas

A panel is the physical counterpart of the control software: the I/O list and the terminal plan are two sides of one document. That is why electrical work usually runs together with industrial automation. On sites that need network infrastructure, cable routing and topology decisions are taken alongside the industrial communication side — where a Profinet segment runs is also a line item in the electrical design.