Tools for Electricians and Plumbers

Six sizing checks that do the arithmetic around a code table without pretending to be one. You read the value out of the edition your jurisdiction has actually adopted; these pages do the derating, the counting and the budgeting that sit on either side of it — in your browser, with nothing sent anywhere.

Why the tables are not in here

It would be easy to embed an ampacity table, a fixture unit list and a gas capacity chart, and it would make every one of these pages a single box you type a load into. We have not, and the reason is not caution for its own sake.

A code table is only correct in the context of an edition, a jurisdiction and whatever local amendments have been made to it. A number typed into a web page has none of that context, does not change when your council adopts a new cycle, and gives no sign when it has gone stale. The failure mode is silent and the consequence is a conductor, a drain or a gas line sized against a rule that is no longer in force.

So the lookup stays with you and your book, where the context lives. What these pages take on is the part that is genuinely arithmetic — and, as it happens, the part that most of the errors are actually in. Nobody misreads 310.16. People forget the termination limit, apply one derating factor and not the other, count a device once, or size a gas segment on its own length.

One thing that turned out to be a formula

While building these we checked whether the ambient temperature correction factors really need a table. They do not. The published figures are computed from √((Tc − Ta) ÷ (Tc − 30)), and deriving it reproduces every printed value to the two decimals the table carries. So that one is calculated rather than looked up — which also means it answers for ambients between the printed rows instead of making you round to the nearest one. Where something is a formula, we would rather derive it than transcribe it. Where it is genuinely a table, it stays in your book.