Everyone has heard the phrase: “it’s shorted.” What does this actually mean and how do you diagnose it? Let’s start answering that question by analyzing the formula for Ohm’s Law.

The Ohm’s Law: Formula is V=I × R

V is Voltage

I is Amperage

R is resistance

You can arrange this equation 3 different ways:

Voltage= Amps × Resistance

Amp= Voltage ÷ Resistance

Resistance= Voltage ÷ Amps

Now, back to the question at hand.

Let’s use an example of  Ohm’s Law with a single phase 5KW(4800 Watts) electric heater at 240vac. If you have been in the HVAC industry for any length of time you have probably memorized that this heater will be pulling 20 amps right? But why?

If you ohm out a 5KW(4800 Watts) heater with a multimeter you will get 12Ω or 12 ohms (ohms is what resistance is measured with).

Using the formula for Amps from above, we can figure out why it is 20 amps.

Amp= Voltage ÷ Resistance

Amps=240vac ÷ 12Ω

Amps = 20

If the resistance of the heater were to become lower, it would cause our amps to increase. In the heat strip drawings: the top heater would represent a good circuit, the second (lower) heater would represent a circuit that the element has sagged and is now touching (in the red circle) which has created a “shorter” path for electricity to flow through.