EXPERT GUIDE | LED driver distance

LED driver distance is an important consideration in every lighting installation with an external driver. In many projects, the LED driver cannot be installed directly beside the luminaire. It may be located above a suspended ceiling, inside an electrical cabinet or in a separate technical room. As the LED driver distance increases, the electrical behaviour of the lighting system changes. Understanding these effects helps prevent voltage drop, unstable dimming, EMC issues and unnecessary maintenance.

The cable is part of the electrical circuit

It is easy to think of the cable as simply carrying power from the driver to the luminaire. In practice, the cable is part of the electrical circuit.

Every metre of cable has resistance, inductance and capacitance. As the cable becomes longer, these properties increase and can influence how the driver and LED module operate together.

This is one of the reasons why driver manufacturers specify a maximum cable length.

What is voltage drop?

Voltage drop is the reduction in voltage that occurs as electrical current travels through a cable.

Every conductor has electrical resistance. Part of the available voltage is therefore lost before it reaches the luminaire. The effect becomes greater when the cable is longer, the current is higher or the cable cross-section is smaller.

In constant voltage systems, excessive voltage drop can cause:

• lower light output
• uneven brightness
• colour differences
• reduced system efficiency

In constant current systems, the voltage drop reduces the voltage available for the driver to regulate the LED module. If the required voltage exceeds the driver’s output range, the driver may no longer maintain the correct current.

What is EMC?

EMC stands for Electromagnetic Compatibility. It describes the ability of electrical equipment to operate correctly without causing or being affected by electromagnetic interference.

LED drivers use high-frequency switching electronics to convert the mains supply into the voltage or current required by the LEDs. These switching signals can travel through the cable between the driver and the luminaire.

As the cable becomes longer, it can become more effective at radiating electromagnetic interference or receiving interference from nearby equipment.

Poor EMC conditions may contribute to:

• unstable operation
• flicker or irregular dimming
• communication problems
• interference with nearby equipment
• failure to meet the tested EMC conditions

For this reason, manufacturers generally recommend keeping the secondary cable between the driver and LED module as short as practical.

Constant current versus constant voltage

The permitted distance also depends on the type of driver.

Constant current drivers

Constant current drivers supply a controlled current, such as 250 mA, 350 mA, 500 mA or 700 mA. They are commonly used with architectural luminaires and COB LED modules.

The driver continuously regulates the current through the LED circuit. Longer cables can affect the available voltage, regulation, dimming performance and EMC behaviour.

Many standard constant current drivers allow only a few metres between the driver and the LED module. Drivers designed specifically for remote installation may allow longer distances.

Constant voltage drivers

Constant voltage drivers provide a fixed voltage, usually 12 V, 24 V or 48 V. They are often used with LED strips and luminaires that contain their own current regulation.

In these systems, voltage drop is usually the main practical limitation. A 48 V system is generally better suited to longer cable runs than a 24 V system because it requires less current for the same power.

However, constant voltage does not automatically mean unlimited cable length. The driver may still have a maximum secondary cable length related to EMC, dimming or internal driver design.

Does a larger cable allow a longer distance?

A larger cable cross-section reduces electrical resistance and voltage drop. It can therefore help when the driver must be installed further from the luminaire.

However, it does not remove every limitation.

A larger cable cannot automatically correct:

• EMC limitations
• driver stability issues
• dimming restrictions
• protection-function limitations
• the manufacturer’s maximum permitted cable length

The cable cross-section must therefore be calculated according to the current, cable length and permitted voltage drop. The result must then be checked against the driver manufacturer’s instructions.

Cable routing also matters

The route of the cable can be just as important as its length.

Long parallel runs beside mains cables, motor cables, frequency converters or communication wiring can increase electromagnetic coupling.

For better system performance:

• keep the positive and negative conductors close together
• avoid unnecessary cable loops
• do not leave excess cable tightly coiled
• avoid long parallel runs beside mains or data cables
• cross other cables at approximately 90 degrees where practical
• keep LED wiring away from strong sources of electrical interference

Why do manufacturers specify a maximum distance?

There is no universal rule stating that every driver can be installed 2, 5 or 10 metres from the luminaire.

The permitted distance depends on the design of the individual driver. Manufacturers test their products under defined conditions, including cable length, cable type, LED load, dimming behaviour and EMC performance.

Two drivers with the same current and power rating may therefore have completely different maximum cable lengths.

The driver datasheet and installation instructions must always be the final reference.

Design recommendations

When designing the position of the driver:

• install the driver as close to the luminaire as practical
• check the manufacturer’s maximum secondary cable length
• calculate the complete outgoing and return cable length
• select the cable cross-section according to the load and distance
• consider both voltage drop and EMC
• review the cable route for possible interference
• keep the driver accessible for maintenance
• provide sufficient ventilation around the driver

Do you need to install the driver further away?

Some projects require a longer distance between the driver and the luminaire. This may be necessary because of limited ceiling space, restricted access, high temperatures or the position of the technical installation.

In many cases, a suitable solution can be found by selecting a different driver, increasing the system voltage, changing the cable cross-section or reviewing the cable route.

However, the complete combination of driver, cable and LED module must be checked before installation.

Do you need to install an LED driver further from the luminaire and are you unsure whether the proposed distance is suitable?

Contact us with the luminaire type, selected driver, required cable length and cable specification. Our technical team can review the application and help you select a reliable solution for your project.

Conclusion

The distance between an LED driver and a luminaire is not simply an installation preference.

As the cable becomes longer, voltage drop increases, EMC becomes more important and the electrical behaviour of the system changes. The result depends on the driver type, output current, system voltage, cable cross-section and cable route.

By considering these factors during the design stage and following the manufacturer’s recommendations, designers can avoid unstable operation, unnecessary losses and preventable EMC problems.