u could use a clamp on ammeter to measure the current draw. Use the same usual amperage ratings, such as 15 amps for 14 gauge wires, for either 120 or 240 volt heaters. The actual total draw must be 80% or less of the wire rating since heaters are "continuous" loads. The full wire rating is based on "intermittent" loads, things not expected to be drawing continuously for more than an hour or so.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!