About EnergyCalcHQ

EnergyCalcHQ publishes free engineering calculators and working notes for electrical, metering and energy work: 51 calculators across 9 subject areas, and 34 written guides. Cable sizing, volt drop, breaker and motor starter selection, transformer and DG set sizing, earthing, power factor correction, solar and storage, tariffs and billing, and Modbus register and float decoding for anyone integrating energy meters. There is also a single line diagram generator that draws a panel from its configuration and exports it as SVG or PNG.

Everything runs in your browser, needs no sign-up, and is free to use.

The site is operated by Divakar B.

Who it is for

Practising engineers, panel builders, contractors and system integrators — people who have to put a number on a drawing and stand behind it. The defaults throughout assume Indian LT practice: 415 V three-phase, 230 V single-phase, IS-series standards, kVA-based maximum demand tariffs. The formulas are general; the assumptions are stated on every page so you can change them for your own supply.

Why another calculator site

Most engineering calculators online give you a number and nothing else. You cannot tell what assumptions were made, which standard was followed, or whether the derating that matters on your job was applied at all. That is fine for curiosity and useless for work you have to sign.

Every calculator here shows the formula, names the standard, and explains what it does not check. The cable sizing tool tells you plainly that it does not run the short-circuit withstand check, because a tool that quietly skips a step is worse than no tool at all.

How a calculator is built

Each one goes through the same four steps before it is published:

1. The formula is fixed first, from the governing standard or from first principles, and it is printed on the page in the same form the calculator evaluates. Nothing is hidden in code that is not shown in the explanation.
2. The result is checked by hand against a worked example, and against published tables where they exist — motor full load current charts, transformer full load currents, cable current ratings.
3. The limits are written down. Every tool states what it does not account for, because the gap between what a calculator checks and what a design needs is where accidents live.
4. The explanation is written for someone who will be challenged on the number in a design review — not a paragraph of filler, but the derivation, the assumptions and the common mistakes.

Where the numbers come from

The calculators follow published standards and conventional practice. The ones referenced most often across the site:

• IS 732 — code of practice for electrical wiring installations; volt drop limits and installation conditions.
• IS 3961 — recommended current ratings for cables.
• IS 3043 — code of practice for earthing.
• IS 1180 — distribution transformers.
• IEC 60898 and IEC 60947 — circuit breakers for household and industrial use, and their trip characteristics.
• IEC 60909 — short-circuit current calculation.
• IEC 60617 — graphical symbols for diagrams, used by the single line diagram generator.
• The Modbus application protocol specification — for register addressing and 32-bit float decoding.

Cable current ratings and volt drop figures on this site are representative values for PVC-insulated armoured cable. Real ratings vary between manufacturers by 5–10 % for the same nominal size and construction. Derating factors follow the conventional ambient, grouping and installation-method corrections.

Who writes the notes

The written guides come from people who build panels and commission systems, not from a content farm. When a post describes a failure mode — a phantom Modbus register, a cable that passed load current and failed under fault, a meter reading 30 % low because the CT ratio was set for a different installation — it is because it happened on a job.

Posts are written to be useful to someone with the problem in front of them, which is why they run to a thousand words or more and include the numbers, the tables and the diagnostic sequence rather than a summary of what the words mean.

Corrections

A wrong number in a calculator that engineers rely on is a serious problem, and we would rather hear about it than not. If you find an error — in a formula, a table, a derating factor or a worked example — write to divarj2@gmail.com or use the contact form. Corrections are made promptly and the page is updated; where a change alters a result, the explanation says so.

What this site is not

It is not a substitute for a qualified engineer. These tools are for preliminary sizing, estimation and checking. They do not constitute a design, and they cannot see the specifics of your installation — the actual cable you are buying, the temperature inside your panel, the fault level at your board, the local supply rules that apply to you.

Before anything here is issued as a design, confirm it against the manufacturer's datasheet for the equipment you are actually purchasing, and have a licensed electrical engineer approve it. That warning sits in the footer of every page because it matters more than anything else on the site.

Your privacy

The calculators run entirely in your browser. The load figures, cable lengths, tariffs and register values you type are never sent to a server and are not stored anywhere. Nothing on this site requires an account.

The site does use analytics and advertising, which involve cookies and similar technologies. What is collected, by whom, and how to opt out is set out in full in the privacy policy.

How the site is funded

The calculators are free and require no sign-up. The site carries advertising to cover hosting and the time that goes into the writing.

Three commitments about that:

• Ads never sit between you and a result. They are placed after content, never among the inputs of a calculator, and never where a mis-tap becomes a click.
• Ads are never disguised as content. Every unit is labelled and visually separated from the page.
• No advertiser has any say in what is published. Nothing here is sponsored, and no product recommendation is paid for. Where a manufacturer is named, it is because the specification matters to the calculation.

Contact

Questions, corrections, or a calculator you wish existed: divarj2@gmail.com, or the contact form. Enquiries are answered by a person.