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Lesson 6 of 6 · 15 minutes · Free

Find the Fault with Measurements

Use voltage and current together to distinguish common circuit faults.

Try the experiment ↓Practice challenge ↓

See the idea

A zero-current reading does not mean every point is at zero voltage. An open load interrupts the path; with no current through the upstream resistor, the node at the open load rises to the ideal supply voltage.

A bypass across the load pulls that node to the return potential. Current is then limited by the upstream resistor. This bench retains that resistor in every fault case, so bypass current is finite; it does not simulate a direct short across an ideal source.

A poor series connection adds resistance. Load voltage and current both fall, while energy is dissipated at the connection. Measurements locate the drop; appearance alone may not identify it.

Vs = Vupstream + Vconnection + Vload I = Vs / Rtotal

Compare a set of measurements against the expected healthy circuit.

Work through an example

  1. Normal: 12 V across two 1,000 Ω resistors gives 6 mA and a 6 V load voltage.
  2. Open load: current is 0 mA, but the voltage across the open load terminals is 12 V.
  3. Bypassed load: load voltage is 0 V and current is 12 mA through the remaining 1,000 Ω resistor. An added 3,000 Ω series connection instead gives 2.4 mA and 2.4 V at the load.

Watch for this

Never infer that equipment is safe to touch from this ideal model. It does not model shock hazards, arc flash, grounding faults or protection coordination.

Predict, then test

  1. Record normal measurements, then inject each fault from the selector.
  2. For each fault, predict current and load voltage before reading the meters. Repair the fault by selecting Normal.

Your virtual bench

Change a setting. See the circuit respond.

Swipe the diagram sideways to explore the connections.

±12 VR1 1000 ΩR21000 ΩReturn reference: 0 V
Source current6 mA
Supply power0.072 W
R1 voltage6 V
Load / R2 voltage6 V

Connection voltage drop: 0 V. Bypass retains R1 as a current-limiting resistor.

Model: Ideal low-voltage DC source and linear resistors; zero wire resistance except the selected connection fault. Values are calculated, not equipment measurements. Browser simulation only—do not connect live equipment.

Check your understanding

An open load in this series circuit gives which ideal readings?

Put it to work

Inject the high-resistance fault with 12 V and R1 = R2 = 1,000 Ω. Locate the largest voltage drop.

Show the worked solution

Total resistance is 5,000 Ω and current is 2.4 mA. The 3,000 Ω connection drops 7.2 V; each 1,000 Ω resistor drops 2.4 V.

Try the experiment and answer the check, then record your completion.