Power · Transformer Calculator

MrSandman.Net — Practical electrical calculators for the modern IBEW wireman.
Field calculators and layout helpers for electrical work.

Quick single-phase transformer planning calculator for current and kVA. Use this for planning and training. Verify final conductor, OCPD, and installation decisions against the current NEC and actual equipment nameplate data.

Calculation mode

Transformer size (kVA)

Primary volts

Secondary volts

Quick result

—

Choose a mode and values.

Primary current: —

Secondary current: —

Turns / voltage ratio: —

kVA result: —

Authority block

Electrical foundation	Transformer apparent power relationship: kVA = volts × amps ÷ 1000 for single phase, and kVA = √3 × volts × amps ÷ 1000 for three phase.
What this version does	Single-phase primary/secondary current planning plus a quick kVA helper.
What this version does not do yet	NEC OCPD sizing, conductor sizing, tap rules, grounding/bonding, or full transformer installation logic.
Field rule	Always verify actual nameplate values and final code requirements before installation.

How this page works

1. In current mode, enter transformer kVA, primary volts, and secondary volts.

2. The page calculates single-phase full-load primary and secondary current.

3. In kVA mode, enter volts and amps to estimate apparent power.

4. Use the result as a planning and study aid, then verify the actual installation against nameplate and code requirements.