Originally Posted by John Schroader

Finally we are on a subject that I actually am competent in. Another reason that the amps might be dropping (besides those mentioned) is the resistive co-efficient to temperature. Many heat elements (most) change resistance as the temperature changes. Some have a positive co-efficient -- resistance rises with temp and some have a negative co-efficient -- resistance drops with temps. This can easily be seen by measuring the resistance of an incandescent (quartz - for exampe) light. Using ohm's law and a cold resistance reading would not give anywhere near the amp draw that an ammeter would indicate. That's because the ammeter only measures the current as it flows (hence the filament is hot). Also ---- clamp type ammeters work well with AC; they barely function at all, and are wildly erratic, on DC. An in line ammeter with a healthy shunt is far more accurate than a clamp type.