Why does the bulb not light up even though there is voltage between the 220V wires?

No Light Emission from the Bulb Despite Detected Voltage Between 220V Wires

The core causes are the failure to form an effective current circuit, damage to the bulb itself, ou, in rare cases, a voltage illusion caused by induced phantom voltage. Below is a detailed analysis of the causes and troubleshooting steps, sorted from the easiest to the most difficult:

1. Faults of the Bulb Itself (Le plus courant)
2. Filament Blowout (Incandescent/Halogen Bulbs)

The internal filament of the bulb burns out due to aging, voltage fluctuations, or frequent on-off cycles. In this case, although voltage exists between the wires, current cannot pass through the filament, and the bulb fails to light up. You can directly replace it with a bulb of the same specification for testing.

2. Damage to the LED Bulb Driver Board

The core component of an LED bulb is the driver power board. If the capacitors on the driver board bulge or the chips burn out, even with a 220V input voltage, it cannot be converted into the low-voltage direct current required by the lamp beads, resulting in the bulb failing to light up.

3. Poor Contact in the Lamp Holder

Oxidation or deformation of the copper sheets inside the lamp holder, or loose contact between the bulb base and the copper sheets, leads to failure of current conduction.

Loose or disconnected wiring terminals of the lamp holder prevent the live wire/neutral wire from being properly connected to the lamp holder. The voltage measured by a multimeter is only “pass-through voltage”.

1. Circuit Loop Faults (Key Reason for Voltage Presence Without Current)

The essence of such faults is that the live wire and neutral wire fail to form a complete closed loop. When measuring voltage with a multimeter, the potential of the live wire can be detected, but no load current can be generated.

1. Switch Malfunction

Oxidation/Ablation of Switch Contacts: After long-term use, the internal contacts of the switch become oxidized or carbonized, causing the circuit to remain disconnected even when the switch is closed, and current cannot pass through.

Switch Controlling the Neutral Wire: Standard wiring requires the switch to control the live wire. Cependant, if it is incorrectly connected to control the neutral wire, the bulb remains connected to the live wire when the switch is off. A multimeter will detect 220V voltage across the lamp holder terminals, but the bulb will still not light up if there is a break in the neutral wire when the switch is closed.

2. Neutral Wire Breakage

This is a high-frequency fault point. A broken neutral wire or oxidized joints at junction boxes, wall bushings, terminal blocks, etc., will cause the following problems:

A multimeter will still detect 220V voltage between the live wire and neutral wire terminals of the lamp holder (the voltage of the live wire is induced to the neutral wire terminal through the bulb filament);

Cependant, current cannot return to the power grid through the neutral wire, and the bulb fails to light up.

Associated Phenomena: Other électrique appliances in the same circuit also fail to work, or the measured voltage of the neutral wire to the ground is abnormal (the normal voltage of the neutral wire to the ground is close to 0V; it may reach tens of volts after a break).

3. Latent Breakage of the Live Wire

Internal breakage of the live wire (par ex., due to aging or damage during threading through a pipe) or severe oxidation of joints results in a “loose connection” État:

When measuring voltage with a multimeter, 220V voltage can be detected due to the multimeter’s extremely high internal resistance;

When the bulb (charger) is connected, the contact resistance at the loose connection point is much higher than the filament resistance. The entire voltage drops at the loose connection point, and the actual voltage across the bulb is close to 0V, so it cannot light up.

III. Voltage Illusion Caused by Induced Phantom Voltage

This situation is relatively special. The voltage between the wires is induced voltage rather than real supply voltage, with the following characteristics:

1. When wires are laid parallel for a long time, the alternating electric field of the live wire induces voltage on the neutral wire or idle lines, and a multimeter (with high internal resistance) will display a voltage of around 220V;
2. Induced voltage has extremely poor load-carrying capacity. Once a bulb is connected, the voltage drops to 0V instantly, and the bulb fails to light up;
3. Identification Method: Perform a loaded voltage measurement with a multimeter (connect a 100W incandescent bulb in parallel across the lamp holder terminals as a load). If the voltage drops sharply to 0V, it is induced phantom voltage.
4. Quick Troubleshooting Steps (La sécurité avant tout, Power Off Before Operation)
5. Replace the Bulb: Replace the bulb with a known good one of the same specification. If the new bulb lights up, the original bulb is damaged.
6. Inspect the Lamp Holder: After powering off, open the lamp holder, check for loose wiring and oxidized copper sheets, and gently pry the copper sheets with a screwdriver to ensure tight contact with the bulb base.
7. Test the Switch: Use the continuity test function of a multimeter to measure the switch. It should conduct electricity when closed and not conduct when open. En même temps, check whether the switch controls the live wire (after powering off, measure the incoming terminal of the switch; the terminal with voltage is the live wire end).
8. Troubleshoot the Neutral Wire: Test whether other electrical appliances (par ex., prises) in the same circuit work normally. If none of them work, focus on checking whether the neutral wire terminal block in the distribution box is loose or oxidized.
9. Distinguish Phantom Voltage: Measure the voltage across the lamp holder terminals with a load. If the voltage disappears, it is induced phantom voltage. You need to check whether the wiring layout is standardized and whether the live wire and neutral wire are laid parallel over an excessively long distance.