The Best Way to Check Whether or Not a Heater is Operating Correctly on the Line

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engraving of wattage and voltage on a Thermal Corporation mica band heater

We received a question from a customer the other day regarding how to check whether or not a heater is operating correctly on the line. This is a great question! But, how do you actually know if a heater is operating correctly or not? Our answer is this: The best and safest way to check a single phase heater that is still on a machine is to…

  1. Turn off power to the heater and disconnect the lead wires.
  2. Find the number engraved on the heater specifying the watts and volts. (See photo)
  3. Measure the resistance between the two lead wires or two post terminals, depending on the heater.
  4. The resistance should be close to the voltage squared divided by the wattage (for you mathematicians out there, here is a formula: R = V^2 / W)

For example: You have a 500 W – 240 V heater.

R = 240^2 / 500

R= 115.2 omhs

Standard tolerances allow for resistance to measure between -10% and +5% of this total when the heater is at room temperature. If the heater is still at operating temperature expect resistances in the range of -5% to +10% of the calculated total.

Have a question for us about your heater? Visit our contact us page or email our engineering department at engineeering@thermalcorp.com!

Written by Kyle Otte
Edited by Shelby Reece
Date Published: 07.19.2018
Last Updated: 09.06.2019