Electrical engineering, safe.
Also called: Circuit design · Electronics design · Schematic design · Hardware engineering
Designing the circuit that drives, senses and controls the product safely, and proving it meets the electrical safety standards a mains appliance must.
The circuit has one job: hold temperature, show it, and fail safe. Power supply, heater drive, sensing loop, interface, and a hardware thermal cut-out that does not trust software. Design it to pass BS EN 61010 and carry UKCA, or it does not ship.
What the electrical engineering is
Electrical engineering turns the function of the product into a working circuit. For a heated appliance that means five jobs: take mains power down to a safe low voltage, drive the heating element, sense the temperature, run a control loop, and give the user a way to set and read it. Every one of those is a design decision with a right and a wrong answer.
The part that separates a hobby build from a product you can sell is safety. A mains kitchen appliance can kill someone if a fault goes the wrong way. The standard that governs it, BS EN 61010, is not a box-ticking exercise; it is the difference between a thermal runaway that scorches a worktop and one that simply switches off. The single most important rule I hold to is that safety must not depend on the firmware being correct. Software has bugs. The cut-out must be hardware.
So the electrical design carries two layers. The control layer does the clever work: read the sensor, compare to setpoint, modulate the heater. The protection layer sits underneath it and does one dumb thing reliably: if the temperature goes past a hard limit, cut the power, no questions, no code involved. If you only build the first layer, you have a science project, not a product.
The compare below is the choice every electronics designer faces on a heated product. The left column is what gets you a demo that works on the bench. The right column is what gets you a product you can legally sell.
- Safety cut-out done in firmware to save a part.
- Mains and low-voltage tracks crowded together on one board.
- No fuse, because “it has never tripped”.
- Feature-rich, never tested against a standard.
- Hardware thermal cut-out, independent of any code.
- Mains contained in one fused, spaced-out module.
- Designed from the schematic to pass BS EN 61010.
- Only the functions that earn their place, all certifiable.
How it fits the bigger picture
Electrical engineering is activity 07.10.06, deep in Stage 07 Engineer. It takes the mechanical layout and the chosen function and turns them into a real circuit. Next comes engineering drawings (07.10.07), which capture the schematic, the board layout and the wiring as the controlled documents a manufacturer can actually build from.
What it can do
It produces a circuit that does the product’s real job and fails safe when something goes wrong. Done properly it gives you a schematic and a board ready to be drawn up, sourced and certified, and a clear path to UKCA marking. It is where the promise “holds 26°C without you thinking about it” becomes physically true.
What it can’t do
It can’t certify itself. A design built to BS EN 61010 still has to be tested and assessed before it carries UKCA, and a clever schematic doesn’t excuse a sloppy build. It also can’t fix a bad mechanical layout: if the sensor sits in the wrong place, no amount of control loop saves the reading.
See the full 10-stage process →
Try it yourself
Sketch your product’s circuit as five blocks: power in, the thing it drives, the thing it senses, the control between them, and the user interface. Then ask the question that matters most: “if the firmware froze right now, what stops this hurting someone?” If the answer is “the firmware”, you have not finished. Add a hardware layer that fails safe on its own, and only then start adding features.
Want help framing the function before the circuit? Start the Free Sprint → and the GPT will walk you through what the product actually has to do.
Your electrical-design checklist
Project notes: the board from Manchester
▸ From the notebook · optional reading
Designing the proofing box circuit with a Manchester PCB partner, and the argument about the thermal cut-out that we were right to lose.
3 min read · click to open
We worked with a small board-assembly partner in Manchester for the proofing box electronics. They had done plenty of low-voltage control work and were comfortable with the ±0.5°C closed loop Dan and Anna needed. The function was never in doubt. The fight, when it came, was about safety.
The corner we nearly cut
The first schematic had the over-temperature protection living in the firmware. Read the sensor, and if it reads too high, the code shuts the heater off. Clean, cheap, one fewer component. On the bench it worked perfectly. I asked the obvious question: what happens if the microcontroller locks up while the heater is on? Silence. That is exactly the failure that scorches a worktop, and possibly worse, in a box left running overnight.
What we changed
We pushed for a separate hardware thermal cut-out: a part that sits in the heater’s power path and trips at a fixed limit with no software involved. It cost a little and added a component. It also meant the design could honestly be built to BS EN 61010 rather than hoped through it. The Manchester partner agreed quickly once the failure mode was on the table; nobody wants their board in a kitchen fire.
The rest fell into line. Mains went into one enclosed, fused module, kept away from the signal tracks. Total draw came in under 30W. The interface stayed deliberately dumb: one rotary encoder, one OLED, no Wi-Fi to add a wireless certification headache and an attack surface nobody asked for. The board went off for assessment and the £149 product carried its UKCA mark on a £38–55 bill of materials, with the cut-out as the part I would never let anyone value-engineer away.
— Engineer stage, project notes, 2026
— Next in Engineer → Engineering drawings