Are you experiencing an issue where your Shelly EM is failing to report power usage on Channel 1 (P1+ / P1-)? You're not alone — and the good news is, there are clear steps you can take to diagnose and potentially fix the problem.
In this article, we break down a real-world issue where Channel 1 on a Shelly EM always displays 0W, even under load, while Channel 2 (P2+ / P2-) works perfectly.
The Issue: Channel 1 Always Reads 0W
A customer recently contacted us with the following scenario:
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CT Clamp connected to Channel 1 (P1+ / P1-) with the arrow pointing towards the load
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Load is active, but no wattage is displayed (always 0W)
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Multimeter confirms good wiring connection
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When the same CT Clamp is moved to Channel 2 (P2+ / P2-), power monitoring works normally
This suggests that the issue lies specifically with Channel 1, not the CT clamp or the wiring.
✅ Troubleshooting Steps for Shelly EM Channel 1 Fault
Follow these steps to isolate and potentially resolve the issue:
1. 🔄 Swap CT Clamps Between Channels
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Move the working CT clamp from Channel 2 to Channel 1
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Keep the clamp orientation the same (arrow towards the load)
If Channel 1 still shows 0W, while Channel 2 continues to work with either CT clamp:
✅ CT clamps are functioning correctly
❌ The issue is isolated to Channel 1 hardware or software
2. 🔌 Check the CT Connector Seating
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Power down the Shelly EM
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Firmly reinsert the CT connector into P1+ / P1-
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Inspect for:
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Loose wires
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Corrosion
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Damaged terminals
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Tug gently on the wires to ensure they're properly seated
3. 🔁 Reset Calibration or Perform Factory Reset
Sometimes a firmware glitch or software calibration error can cause faulty readings.
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Try a soft reset first
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If that doesn’t help:
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Perform a factory reset
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Reconfigure both channels from scratch using the Shelly web interface
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4. 🖥️ Use the Web Interface for Diagnostics
Log into the Shelly EM’s local web UI:
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Navigate to Device Status > Channel 1
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Watch for:
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Flickering current or voltage readings
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Any raw value anomalies (e.g. 0A current with non-zero voltage)
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This can help determine if there’s a sensor fault or firmware-related bug.