Reading a distribution panel schema — Eaton & Hager example

A schema in a textbook is tidy; a real panel on a mobile installation or in a greenhouse control cabinet rarely is. Below is a fully worked example of two different panel types — an Eaton panel and a Hager panel (TN-S) — with the kind of questions an examiner or a colleague could realistically ask you about it. The goal isn't to memorise these exact group numbers — the installation you meet tomorrow will have different ones — but to master the reading principle: which symbol belongs to which function, and why something is wired the way it is.

Eaton panel — group by group

The incoming supply runs through a 160A/4-pole main switch, with earth points drawn both before and after this switch.

Hager panel (TN-S) — group by group

Incoming: main disconnector S1 "HACV", 125A.

Four questions you could realistically be asked about this kind of schema

1. Why does group 7 (Eaton) have both a switch and a fuse in series, while other groups only have one protective device? Double protection in series shows up when an older or modified group has been extended: the fuse protects against overcurrent/short-circuit, while the separate switch serves as a visible switching/disconnection point. Never assume this is a mistake without following the diagram — first confirm both parts are genuinely in series within the same group before judging either one redundant.

2. What's the difference between the 30mA and 300mA RCDs on this schema? 30mA (Q1, Q3, Q4) is ordinary personal protection, directly upstream of the end groups. 300mA (Q2, Q5) is selective/time-delayed: it must not trip before a downstream 30mA device (such as F18 under Q2) already has. That way, a leakage fault only drops the faulty end group, not the whole branch above it — nested selectivity across two protection tiers.

3. Why does group Q4 have a type B RCD instead of type A? Type A protects against AC and pulsating-DC leakage current. Type B additionally protects against smooth (filtered) DC leakage current — which can be produced by electronics with frequency control (VFD/variable-speed drive), EV charging equipment, or certain electronically-driven hand tools. On a mobile installation, you don't know in advance exactly what will be plugged in, so the more universal (and more expensive) type B is chosen as a precaution.

4. Which group feeds a motor, and with what specific component is it protected? K2 (Eaton, compressor) and K30 (Hager, motor) both run through an MBS (motor protection switch) rather than a plain circuit breaker — this protects the motor individually against overload and provides manual start/stop control (1/0 position + jog button for momentary starts).

Diagram notation: reference triangles

At the top of each sheet of a multi-sheet schema (as in this Hager example, spread across several sheets), you'll often see small triangles marked with a code such as "R1 1-A,14". These aren't circuit components — they're continuation references: "this line continues on sheet 1, column A, row 14" — the cross-numbering convention that ties a schema together across multiple sheets. Follow this notation before concluding a line "goes nowhere" — it usually just continues on another sheet.

Why this matters in practice

You'll meet this kind of mixed, realistic schema in scenarios such as: isolating a single group in a greenhouse control cabinet while the rest of the installation stays live, replacing a variable-frequency drive (VFD) on a pump or fan (with a DC-bus wait time — see the motor-replacement guide), checking phase rotation on a CEEform connection before commissioning, an RCD tripping under humid greenhouse conditions, or multiple electricians working together under a single lock-out with a multi-lock hasp.

Related: Safely replacing a three-phase motor, Perilex, CEEform and phase rotation, Distribution boards & selectivity, Danger zone and approach zone.

Practical rule of thumb

Always read an unfamiliar schema in this order: (1) follow the incoming main switch and the earthing system (TN-S/TT), (2) identify, for each branch, which RCD sits upstream and at what current rating/type, (3) follow each group down to its load (socket, CEEform, motor via MBS), (4) check for shared protection and nested selectivity before disconnecting a group or tracing a fault. Master the principle, and you can read any brand of panel — not just these two.