Lastsocket: Voltage Drop

Last Socket

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About this app

Does this cable pass? Lastsocket is a voltage drop and cable size calculator for electricians and installers in the UK, Ireland and Europe. Type the current, the length and the cross-section; get the drop in volts and percent and a PASS or FAIL against the limit in your national pack — BS 7671, NEN 1010, DIN VDE 0100, NF C 15-100 or IEC typical — with the rule cited under the number.

SHOWS THE WORKING
Every result opens a working card: conductor resistance at operating temperature (IEC 60228 values, 70 °C PVC or 90 °C XLPE), the formula, every input, and the list of what was not checked. A senior can audit a junior from the phone. Share any result as text or, with Pro, as a PDF with the working.

PASS OR FAIL, NOT A BARE NUMBER
All five national packs are free. A pack changes the limit, the labels and the rule cited — never the formula. Pick BS 7671 and you get 3 % lighting / 5 % other on a public supply (6 % / 8 % private); pick DIN VDE and the limit is 3 %, citing DIN 18015-1. A custom limit is always one tap away.

TEN CALCULATORS, ONE JOB PER SCREEN
• Voltage drop — single-phase, three-phase and DC (12 / 24 / 48 V), plus solve for the maximum length
• Cable size — the smallest cross-section that passes both gates: Iz after correction factors, then voltage drop (Pro)
• Ampacity — your own Iz from the book, checked against the load; bundled tables and factors with Pro
• DC drop, Ohm's law and power, diversity
• Pipe size, pressure loss, thermal expansion, room heat loss
• Unit converter and a Sources screen that says where every number comes from

FREE IS A REAL JOB. PRO IS THE APP DOING THE LOOKUP.
If you type it or pick it, it's free. If the app looks up a table or walks the sizes for you, it's Pro — a single €9.99 purchase, restored by Google Play on a new phone. No subscription. No account. Future table updates in this version are included.

WORKS IN THE VAN
Everything runs on the phone. No signal needed, no sign-in, no analytics, no data collected. Your last five jobs are kept free; fifty with Pro, with CSV export.

A DESIGN AID, NOT THE CODE BOOK
Lastsocket does not replace the applicable installation standard, manufacturer data or a qualified person's judgement. The bundled current-carrying-capacity values are a small subset consistent with IEC 60364-5-52 Annex B (methods A1, B2, C and E, PVC copper, to 50 mm²), not a reproduction of any national table. Always confirm Iz in the current edition of your standard. Short-circuit withstand, earth-fault loop impedance and disconnection time are not checked, and the app says so on every result.

Sources, limits and the full privacy policy: lastsocket.com

What’s new

First release. Voltage drop, cable size, ampacity and seven more calculators with the working shown and a pass/fail against your national pack. Works offline.