WiremanWireman · Find a short by splitting the circuit: troubleshooting for electricians · 2023 NEC ·
Find a short by splitting the circuit
Cut the circuit in half at a box, test each half, and keep halving until the short has nowhere to hide.
Before you start
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How it works
A short could be anywhere along a circuit, but you don’t have to open every box. Open one near the middle, separate the cables, and test which half still reads shorted. Each split throws away half the circuit, so even a long run with a dozen boxes takes only three or four splits. It’s the same idea as guessing a number by asking “higher or lower.”
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Have you confirmed the short is in the wiring?
- Yes, still shorted with all loads offTest: Take a baseline reading at the panelExpect: A healthy circuit with loads off reads OL on every pair.
- One pair reads near 0 ΩTest: Split at a box near the middleExpect: The short shows up in one part only.
- Short is between the panel and this boxKeep splitting the shorted part the same way. Where does it end up?
- In one cable between two boxesTest: Inspect the cable run
- Yes, found the damageDamaged cable
- No, it’s hidden in a finished wallFault inside a hidden cable
- At one box or deviceThe short is at this box
- At a light fixture or fanShort in a fixture or fan
- In one cable between two boxesTest: Inspect the cable run
- Short is in an outgoing cableKeep splitting the shorted part the same way. Where does it end up?
- In one cable between two boxesTest: Inspect the cable run
- Yes, found the damageDamaged cable
- No, it’s hidden in a finished wallFault inside a hidden cable
- At one box or deviceThe short is at this box
- At a light fixture or fanShort in a fixture or fan
- In one cable between two boxesTest: Inspect the cable run
- Both halves clear nowThe short is at this box
- Short is between the panel and this boxKeep splitting the shorted part the same way. Where does it end up?
- Tens to hundreds of ohmsSomething is still connected
- All OL, but it still tripsNot a hard short: an insulation or intermittent fault
- One pair reads near 0 ΩTest: Split at a box near the middleExpect: The short shows up in one part only.
- No, not yetRule out the loads first
- Yes, still shorted with all loads offTest: Take a baseline reading at the panelExpect: A healthy circuit with loads off reads OL on every pair.