Published
- Sizing the DC cable between PV modules and the inverter: the parts of IEC 62548 that get left out — IEC 62548:2016 names three criteria for a PV DC cable and then says the largest result applies. Five of the steps inside those criteria are routinely skipped, and each one moves the answer by a whole cable size: the…
- One schematic, thirteen studies: where Grid Tools stands — What runs today in the schematic workspace, which benchmarks it is checked against, what the free tier covers, what is still a stub — and what to tell us to build next.
- The kvar is the easy part: sizing a capacitor bank in calculator #005 — A 900 kW plant corrected from 0,81 to 0,95 — with the hand check, the 525 V nameplate trap, the 1,43 I_N rule of IEC 60831, and the three failure modes the sizing formula cannot see.
- One earthing system, two ways to be killed — Earth fault and lightning on the same substation: permissible touch voltage per IEC 61936-1 and IEEE 80, the LPS geometry of IEC 62305-3, and a worked 132/11 kV site where the crushed rock decides both checks.
- TN, TT, IT: three letters that decide how a fault clears — The system earthing arrangements of IEC 60364-1 drawn out, with the disconnection rule each one brings with it.
- Earthing grid: touch voltage decides, not resistance — A 60x40 m substation grid solved per IEEE 80 in calculator #003 — it fails on touch voltage at a 10 m mesh, passes at 5 m, and every step is reproduced by hand.
- Short-circuit, bus by bus: an 11/0.4 kV substation in calculator #002 — An 11 kV supply, a 1000 kVA transformer and 50 m of LV cable, solved per IEC 60909 — plus an element-by-element check against the worked example of IEC TR 60909-4.
- Cable ampacity in a real trench: why the table does not apply — Two rows of 240 mm2 cables in one trench solved per IEC 60287, a hand calculation checked against IEC 60502-2 Table B.2 across every size, and why a grouping factor cannot describe your layout.
- Voltage drop, end to end: a worked feeder in calculator #001 — A two-segment pump feeder solved per IEC 60364-5-52, then repeated by hand and checked against IEC 60228 conductor resistances and Annex G.
- Dyn11 decoded: reading a transformer connection symbol — What each letter and the clock number mean in IEC 60076-1, including the notations most people never meet: YNa0+d, YNd11(d1), III and iii.
- Icu, Ics, Icw: what a breaker rating actually promises — Four short-circuit ratings, one selectivity limit current, and the difference between a breaker that survives a fault and one that is finished by it - per IEC 60947-2.
- IP and IK, digit by digit - and the trap in IPX9 — What each numeral of an enclosure code is actually tested for, why IP66 does not imply IP67, and what the code deliberately says nothing about.
- The two conditions of 433.1 - and the one everybody forgets — Overload protection in IEC 60364-4-43 is two inequalities, not one. The second is about the device conventional operating current, and it is the one that fails.
- 0,4 seconds: what automatic disconnection really requires — Table 41.1 in full, which circuits it applies to, the impedance condition behind it, and why an RCD needs several times its rated residual current to make the time.
- Site conditions, honestly: the climatic design basis in one run — 346 parameters for any point on earth, with the one rule that keeps a design basis honest — a statistic of the record is never printed as a design action. A worked coastal site in Dubai, from the design ambient to the…
- LV cable sizing: the factor picks the section, not the load — A 160 A feeder sized from the IEC 60364-5-52 Annex B tables: how Ca, Cg and Cs are assembled, why the same cable moves from 70 mm2 to 185 mm2 when it goes underground, and which part of a route governs under clause…
- A CT can fail from too little burden: the secondary check in calculator #006 — A 1200/1 CT with a protection and a metering core, checked per winding: how the connected burden is assembled, why the actual ALF is not the nameplate ALF, which fault scenario governs, and the 25 % burden floor of IEC…
- The earth fault can be the bigger one: LV short-circuit in calculator #012 — A 400 V network solved per IEC 60909-0 at two busbars: why I″k1 exceeds I″k3 on a Dyn-fed board, how the minimum earth-fault current differs from the maximum, the two permitted peak-current methods and the 15 % between…
- One rating, three consequences: transformer sizing and selection — A 1250 kVA unit sized, then checked where it matters: the IEC 60076-5 Table 1 impedance floor, the K_T correction that raises the fault current by 3 %, the ±10 % impedance tolerance of IEC 60076-1 that turns 37,89 kA…
- The 40 °C nobody reads: motor sizing in calculator #009 — A 72 kW load sized to a 90 kW IE3 motor: efficiency taken from IEC 60034-30-1 rather than guessed, DOL against VFD starting (952 A and 3,67 % dip against 238 A and 0,94 %), and the IEC 60034-1 Table 11 assumption about…