Intro – Series Circuit Rules
When troubleshooting series circuits, you can rely on certain rules based on Ohm’s law. Rule #4 is most important when troubleshooting series circuits with only one load. This is because a break in the circuit represents “infinite” resistance. That break will thus have the full supply voltage across it.
Illustration
Below is an illustration of how electricity behaves in a series circuit. The circuit on the right applies to the most-often encountered case (Rule #4) where there is a break in the circuit and the full supply voltage is measured across that break.
Applying Limits to Show how the Voltage Divider Rule Applies to Open Components
From a practical perspective – a circuit with an open component has no current flow. Thus there is no voltage drop across R1 (the load). That leaves the entire supply voltage across the fictitious R2, the open component with infinite resistance.
However, for geeks that want to see the math behind how the common voltage divider rule applies to open components, we can use the limit as R2 approaches infinity where Vs is the supply voltage and VR2 is the voltage across the open component. The result is that VR2 = Vs:
Electrical Troubleshooting Equipment
Some useful tools for electrical troubleshooting are:
A clamp-meter with LowZ, temperature, capacitance, frequency, diode check, and non-contact voltage testing (like a voltage pen).
Click Here for a suggested product that meets all of these requirements.
A voltage pen for testing the presence of AC voltage above the ground potential.
Click Here for a suggested product.
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