Ampmeter testing of electric furnace

Heating · Radiant Heating · printed page 203 (PDF page 204)

Book index entries

Amp Meter Testing of Electric Furnace Electric Current Draw – Testing for Electric Furnace Electric Furnace – Testing Current Draw Electric Heating Systems

Text in the illustration

hot air plenum
heating elements (typically 5 kw each)
25 kw electric furnace
electrical supply
blower
cold air return
B
individual heater element lead wires can be tested to determine which one (or more) is inoperative if the overall current draw is less than expected
make sure all the elements have had ample time to come on and watch out for staged furnaces
A
clamp the ampmeter around one of the main wires at the furnace or electrical panel to check that all of the heating elements are working (e.g. a 25 kw furnace should draw 104 amps at 240 volts)
note:
this test goes beyond the Standards

Generated explanation

A cutaway electric furnace shows a blower above the cold air return, resistance heating elements at the top, and a hot air plenum. Two clamp-on ammeters illustrate testing the main supply conductor for total current draw and an individual heater element lead for element current draw. The annotation gives an expected draw of 104 amps at 240 volts for a 25 kw furnace and explains that individual leads can be tested to locate inoperative elements when total draw is low. It cautions that elements need time to energize, particularly in staged furnaces, and notes that this test goes beyond the Standards.