LED Tube Light Connection Diagram: Ballast Bypass, Single-Ended & Double-Ended Wiring

LED Tube Light Connection Diagram: Ballast Bypass, Single-Ended & Double-Ended Wiring — interactive diagram. Open it in the editor to customise components and wiring.

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Understand how to wire LED replacement tubes using ballast bypass (Type B) wiring in single-ended and double-ended configurations, with shock-safety requirements for each method.

Retrofitting LED tubes into fluorescent luminaires is not simply a plug-in swap. The fluorescent ballast — magnetic or electronic — was designed to preheat electrodes and then strike and regulate a gas-discharge arc. An LED tube does not use a ballast, and if a ballast is left in circuit with an LED tube, the ballast consumes wasted energy, generates heat, and may cause the LED driver within the tube to fail prematurely or produce flicker.

Type B LED tubes are designed for ballast bypass (also called direct wire or re-wire). The ballast is removed entirely, and mains voltage is connected directly to the lamp holders at one or both ends of the fitting. This is the most reliable and energy-efficient configuration because no energy is wasted in a ballast. It does, however, require rewiring the luminaire, and this must only be performed by a qualified electrician — the resulting installation carries mains voltage at the lamp holders.

Single-ended wiring (one live/neutral end) is considered the safer ballast-bypass method for end-users because only one end of the tube carries voltage. The far end of the tube has no connection. The tube itself has internal wiring routing both the live and neutral through its own body. The critical safety requirement is that single-ended tubes must be installed in holders that match the correct powered end — inserting a single-ended tube backwards leaves mains voltage on the 'dead' holder pins with no return path, potentially energising metal lamp holder contacts that a person could touch.

Double-ended wiring (live at one end, neutral at the other) means both sets of lamp holder pins carry mains voltage — one end live, the other neutral. This requires extra care during installation and replacement: the tube must be removed with the circuit isolated (breaker off), because touching either end simultaneously creates a path through the body. Double-ended wiring is common in industrial retrofits because it matches the existing pin layout of many magnetic ballast fittings more directly.

Type A LED tubes contain an internal driver compatible with specific ballast types; Type A+B tubes work on compatible ballasts and in bypass mode. This document addresses Type B bypass wiring only.

All rewiring of luminaires must comply with IEC 60598, IEC 60364, BS 7671, NEC Article 410, or the applicable national wiring regulations, and must be performed by a qualified electrician.

How to wire led tube light connection diagram

Isolate the circuit and verify it is dead at the luminaire Switch off and lock out the circuit breaker supplying the luminaire. Use a non-contact voltage tester or a multimeter set to AC voltage to verify that no voltage is present at the luminaire before opening it. This is a mandatory safety step — capacitors in electronic ballasts can retain charge briefly even after isolation.
Remove the fluorescent tube and access the wiring compartment Remove the diffuser cover if fitted. Rotate and remove the fluorescent tube. Remove the luminaire end caps or wiring compartment covers to expose the ballast and starter (if magnetic type).
Identify and remove all ballast and starter components Disconnect all wires from the ballast. Note or photograph the existing wiring before disconnecting. Remove the ballast, starter(s), and any ballast-specific wiring. On older magnetic ballasts, check the ballast casing for a PCB warning label — if present, treat as hazardous waste and dispose of through an approved channel.
Wire the lamp holders for the appropriate bypass configuration For single-ended wiring: connect line (live) and neutral to both pins of the powered-end holder. Leave the far-end holder pins unconnected. For double-ended wiring: connect line to both pins of one end holder and neutral to both pins of the opposite end holder. Use appropriately rated wiring and terminals. Replace shunted holders with non-shunted holders if required by the tube type.
Fit an appropriate warning label inside the luminaire Most LED tube manufacturers supply a retrofit warning label with the product. If not, create or purchase a label stating: 'MODIFIED FOR LED TUBES ONLY — DO NOT INSTALL FLUORESCENT TUBES — MAINS VOLTAGE AT LAMP HOLDERS.' Affix this label permanently inside the wiring compartment.
Install the LED tube in the correct orientation For single-ended tubes, orient the powered end (usually marked or indicated in the installation instructions) to the end of the fitting that carries line and neutral. Installing backwards will leave a live holder exposed at the un-wired end with no circuit path, which is a safety hazard and will prevent illumination.
Restore power and test, then document the installation Restore the circuit breaker. Verify the tube illuminates correctly with no flicker. Record the retrofit in the maintenance log: date, tube model, installer, and wiring configuration (single-ended or double-ended). This is required for warranty and compliance purposes.

Specifications

Mains supply voltage (typical)	230 V AC ±10% (Europe, UK, Australia, SA); 120 V AC (North America) — verify tube rating
Tube length and wattage (T8 common sizes)	600 mm (2 ft) ~9 W; 1200 mm (4 ft) ~16–18 W; 1500 mm (5 ft) ~20–22 W
Base type (T8 standard)	G13 bi-pin, 13 mm pin spacing
Lamp holder pin isolation (bypass requirement)	Non-shunted (pins electrically independent within holder)
Internal wiring cable rating	Rated for mains voltage; minimum 1.0 mm² cross-section — confirm against applicable wiring code
Operating temperature range (typical LED tube)	−20 °C to +45 °C ambient — confirm product datasheet
Colour rendering index (CRI) — typical	Ra ≥ 80 (good commercial grade); Ra ≥ 90 for colour-critical applications
Rated lifespan (typical Type B LED tube)	25 000–50 000 hours at rated conditions — confirm product datasheet

Safety warnings

MAINS VOLTAGE AT LAMP HOLDERS: After ballast bypass, the lamp holders carry 230 V AC (or local mains voltage). Always isolate and lock out the circuit breaker before replacing a LED tube. Warn all building occupants and maintenance staff that the fitting has been modified — this is why the warning label is mandatory.
NON-SHUNTED HOLDERS REQUIRED for single-ended wiring: Using shunted holders (where both pins are internally joined) in a single-ended installation means both ends of the tube are at the same potential, defeating the shock-safety advantage of single-ended wiring and potentially damaging the tube driver.
DO NOT install fluorescent tubes back into a bypassed luminaire. Connecting a fluorescent tube directly to mains voltage without a ballast will cause immediate failure and may result in fire or explosion.
Earth bonding of the luminaire body must be maintained throughout the retrofit. Never remove or disconnect the earth conductor from the luminaire chassis.
All rewiring of luminaires must be carried out by a qualified, registered electrician and must comply with the applicable national wiring standard (IEC 60364, BS 7671, NEC Article 410, AS/NZS 3000, or equivalent). The work must be inspected and recorded as required by local regulation.

Tools needed

Non-contact voltage tester (to verify circuit is dead before working)
Digital multimeter (AC voltage, resistance)
Screwdrivers (flat and Phillips for luminaire covers and terminal access)
Wire stripper (suitable for 1.0–1.5 mm² cable)
Insulated crimp terminals or appropriate connector tool
Lockout/tagout device for circuit breaker
Permanent marker and self-adhesive label (for retrofit warning label if not supplied)

Common mistakes

Leaving the old ballast in circuit with the bypass tube: The ballast continues to draw power, generates heat, and shortens LED driver life. Some combinations cause sustained flicker. The ballast must be physically removed.
Installing a single-ended tube in the wrong orientation: A single-ended tube installed backwards leaves live lamp holder contacts exposed at the far end with no load connected. Anyone touching those exposed pins while simultaneously touching earth completes a dangerous circuit.
Using shunted lamp holders with single-ended bypass wiring: Shunted holders connect both pins internally. When used with a single-ended tube where one pin carries live and the other neutral at the powered end, a short circuit occurs immediately. Non-shunted holders are required.
Not fitting a retrofit warning label inside the luminaire: Future electricians may not know the fitting has been modified. Without the label, a fluorescent tube could be installed into a mains-direct socket, causing an immediate fault or fire.
Failing to verify that the circuit is dead before opening the wiring compartment: Electronic ballasts contain capacitors that can retain significant charge for several seconds after isolation. Test with a non-contact tester before touching any wiring.

Troubleshooting

LED tube does not illuminate at all: Cause: Tube installed in wrong orientation (single-ended), shunted holders preventing correct driver operation, wiring error leaving no complete circuit through the tube, or blown circuit breaker Fix: Isolate the circuit. Verify the tube is oriented correctly per the manufacturer's marking. Check for voltage at the appropriate holder pins with a multimeter (with circuit live — test quickly and safely). Verify holders are non-shunted. Check that line and neutral are connected to the correct ends.
LED tube flickers or flashes: Cause: Ballast still in circuit (Type B tube not compatible with ballast), loose connection at lamp holder pins, incompatible dimmer switch on the circuit, or failing LED driver Fix: Isolate and confirm the ballast has been completely removed and disconnected. Check and tighten all lamp holder pin connections. Verify the circuit has no dimmer switch (Type B bypass tubes are not dimmer-compatible unless specifically rated). If still flickering with all these checks passed, replace the tube.
Circuit breaker trips immediately when tube is installed and power restored: Cause: Short circuit in the bypass wiring — most likely a shunted holder connecting line and neutral, a wiring error crossing line and neutral at the same holder, or a damaged tube driver Fix: Isolate the circuit. Remove the tube and restore power — if the breaker holds, the fault is in the tube or the holder wiring. Check both holders for correct non-shunted pin isolation. Verify that line and neutral are not connected to the same holder in double-ended wiring.

Frequently asked questions

Why must the ballast be completely removed in a bypass installation?

An operating ballast with no fluorescent tube load can overheat and fail, sometimes causing a fire or releasing toxic PCB compounds from older magnetic ballasts. Even if the LED tube appears to function with the ballast in circuit, the ballast wastes 5–25 W continuously and shortens LED driver life. Complete removal is mandatory for safety and warranty compliance.

What is the shock hazard difference between single-ended and double-ended wiring?

In a correctly wired single-ended installation, touching one end of the tube holder gives access to live or neutral, but touching both ends simultaneously is required to complete a circuit through the body — unlikely with a correctly oriented tube. In double-ended wiring, one end is live and the other is neutral; replacing a tube on a live circuit means one hand near live pins and the other near neutral pins — always isolate before replacement.

Can I mix single-ended LED tubes and double-ended LED tubes in the same fitting?

No. Single-ended and double-ended bypass wiring configurations are not interchangeable. The internal wiring of the luminaire must match the tube type precisely. Fitting a single-ended tube into a double-ended wired fitting means the 'neutral' holder at the far end will actually have no connection, while the driver inside the tube expects neutral on those pins — the tube will not illuminate and may be damaged.

Do I need to label the fitting after a ballast bypass retrofit?

Yes. Most national codes and the LED tube manufacturer's instructions require a warning label inside the luminaire stating that the fitting has been rewired for LED use only and that fluorescent tubes must not be reinstalled. Without this label, a future maintenance electrician could install a fluorescent tube, creating a shock or fire hazard.

What lamp holder type do T8 LED tubes require?

T8 LED tubes use G13 bi-pin holders (two pins, 13 mm spacing). T5 LED tubes use G5 holders (two pins, 5 mm spacing). Verify the holder type is correct for the tube diameter and ensure shunted holders (where both pins are internally connected) are replaced with non-shunted holders for single-ended wiring, as shunted holders defeat the single-ended safety advantage.

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