# Wiring & Measurement ### ⚡Quick Fixes
Negative Active Power Reading A negative active power value indicates that energy is flowing in the reverse direction. This can be a normal operating state or an installation error. Please check the following scenarios based on your setup: **1. Solar PV Export (Normal Operation)** * **Cause:** If you have a solar panel or wind generation system, a negative value simply means your system is generating more power than your home is consuming, and the surplus energy is being exported back to the grid. * **Solution:** No action required. This is normal behavior for bi-directional energy measurement. **2. SDM Series: CT Clamp Reversed** * **Cause:** For meters using external split-core Current Transformers (SDM series), the CT clamp is installed backward on the wire. * **Solution:** Check the directional arrow printed on the CT clamp. The arrow **must point towards the load** (the appliance consuming power). Unclip and reverse the CT direction if necessary. **3. SPM Series: Wire Threaded Backward** * **Cause:** The SPM series features a pass-through (solid-core) design. If the main wire is threaded through the meter's Ø9.6mm hole in the wrong direction, the reading will be reversed. * **Solution:** Check the directional arrow printed on the SPM device casing. Turn off the main breaker, disconnect the wire, and either **flip the device** or **thread the wire through from the opposite side** so that the actual current flow aligns with the arrow. **4. Phase Mismatch (Multi-Phase Systems)** * **Cause:** If you are measuring a 3-phase or split-phase system, the current sensor (CT or SPM device) might be installed on a different phase than its corresponding voltage reference (e.g., measuring the Phase B wire while powered by the Phase A voltage terminal). This phase angle mismatch will result in incorrect, often negative, power readings. * **Solution:** Double-check your wiring map. Strictly ensure that the current measurement aligns with the correct voltage source (L1 to L1, L2 to L2, etc.).
Displayed Power ≠ Voltage × Current **Cause:** The value you manually calculated ($$V \times I$$) is **Apparent Power (VA)**. However, the meter and the app display the actual **Active Power (W)**. **Explanation:** Active Power takes the appliance's efficiency into account using the Power Factor (PF): $$Active\ Power = V \times I \times PF$$ For most household appliances (e.g., AC units, LED drivers), the Power Factor is less than 1.0. Because of this, the actual Active Power will always be lower than simply multiplying Voltage by Current. **Note on SPM Tuya Version:** The Tuya app interface does not display the Power Factor (PF) value, which often causes this manual calculation mismatch. Rest assured, the meter's internal chip automatically includes the PF in its calculations, ensuring the displayed Active Power is 100% accurate.
### 🛠️ Detailed Guides * [Measurement Failure with Heat Pumps](/troubleshooting/electrical-1/measurement-failure-with-heat-pumps.md) `[SPM/SDM Products]` * [Phase Mismatch (Crossed Phases) in 3-Phase Meters](/troubleshooting/electrical-1/phase-mismatch-crossed-phases-in-3-phase-meters.md) `[SPM/SDM Products]`
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