• 19 Aug 2026

How to Reduce Voltage Drop in DC24V Underwater Lighting Systems?

How to Reduce Voltage Drop in DC24V Underwater Lighting Systems?

DC24V underwater lights are widely used for fountains, landscape water features, pools and architectural water features.

However, because DC24V is a relatively low operating voltage, voltage drop becomes an important consideration when underwater lights are installed far from the power supply.

For example, a fountain may have:

• 20–50 underwater lights

• Long cable runs

• RGB or RGBW fixtures

• Multiple lighting zones

• DMX512 control

• Centralized power supplies

If the cable is too small or the circuit is poorly designed, the voltage at the farthest fixtures can be lower than the voltage at the power supply.

This may cause:

• Reduced brightness

• Uneven illumination

• RGB color differences

• Flickering or unstable operation

• Poor lighting consistency

The good news is that voltage drop can be controlled through proper power distribution, cable sizing, circuit design and installation planning.

What Is Voltage Drop in a DC24V Underwater Lighting System?

Voltage drop is the reduction in electrical voltage that occurs as current flows through the resistance of a cable and its connections.

The basic relationship is:

V = I × R

where:

• V = voltage drop

• I = current

• R = resistance

This is a basic application of Ohm's law.

For low-voltage systems, the same amount of cable resistance can represent a much larger percentage of the supply voltage.

This is why voltage-drop management is particularly important for DC24V LED lighting.

Why Is Voltage Drop More Important at DC24V?

Consider two systems with the same 240W load.

DC24V

240W ÷ 24V = 10A

AC220V

240W ÷ 220V ≈ 1.09A

The DC24V system requires much higher current for the same power.

Higher current passing through cable resistance creates greater voltage drop.

This is one reason low-voltage lighting systems require careful cable and distribution planning. Fluke's low-voltage guidance similarly illustrates that the same conductor resistance has a much greater effect on a lower-voltage load.

What Problems Can Excessive Voltage Drop Cause?

For an underwater lighting project, excessive voltage drop can create several visible problems.

1. Reduced Brightness

A fixture at the end of a long cable may not receive the intended operating voltage.

The result can be lower light output.

2. Uneven Lighting

Fixtures close to the power supply may appear brighter than fixtures farther away.

This is especially noticeable in:

• Long fountains

• Linear water features

• Large landscape ponds

• Architectural water features

3. RGB Color Inconsistency

For RGB underwater lights, voltage problems can affect the visual consistency between fixtures.

For example:

Light 1 → Bright Blue

while:

Light 15 → Darker Blue

This creates an uneven visual effect.

4. Flickering or Unstable Operation

If the voltage at the fixture is outside its specified operating range, the fixture may not perform correctly.

5. Poor DMX512 Lighting Results

DMX512 controls the lighting effect, but it does not compensate for inadequate power distribution.

You can have a perfectly programmed DMX512 system and still have poor results if the underwater fixtures do not receive stable power.

How to Calculate Voltage Drop?

A simplified DC voltage-drop calculation is:

Voltage Drop = Current × Cable Resistance

For a complete two-wire DC circuit, remember that current travels out to the fixture and returns to the power supply.

Therefore, the resistance of the full circuit path should be considered.

Example

Suppose:

• Load current = 10A

• Total circuit resistance = 0.2Ω

Then:

Voltage Drop = 10A × 0.2Ω = 2V

A DC24V system would have approximately:

24V − 2V = 22V

at the load under that condition.

Whether 22V is acceptable depends on the actual fixture's specified operating range.

Step 1 — Calculate the Total Lighting Current

Before calculating voltage drop, determine the current.

Use:

Current = Total Power ÷ Voltage

For example:

20 × 12W underwater lights

Total power:

20 × 12W = 240W

At DC24V:

240W ÷ 24V = 10A

Therefore, the system requires approximately:

10A

at full rated load.

Step 2 — Determine the Cable Length

Cable length is extremely important.

For example:

Project A

Power supply → underwater lights:

10 meters

Project B

Power supply → underwater lights:

50 meters

The second installation will generally have more cable resistance and therefore greater voltage drop, assuming the same conductor type and size.

For DC24V systems, the designer should consider the complete current path, not just the one-way distance.

Step 3 — Choose the Correct Cable Size

One of the most effective ways to reduce voltage drop is to use a cable with lower resistance.

In general:

Larger conductor → Lower resistance → Lower voltage drop

For a long DC24V fountain circuit, using a larger cable can significantly reduce voltage drop.

However, cable selection should not be based only on voltage drop.

It should also consider:

• Current capacity

• Installation method

• Temperature

• Cable insulation

• Environmental conditions

• Local electrical requirements

• Waterproofing

• Mechanical protection

For underwater lighting, cable construction and waterproof connections are particularly important. IEC 60598-2-18:2022 includes requirements concerning wiring and waterproof cable options for luminaires used in water or in contact with water.

Step 4 — Reduce the Cable Distance

Another effective method is simply to reduce the length of the DC24V cable.

Instead of:

Power Supply

↓

50m Cable

↓

Underwater Lights

consider placing the power supply closer to the lighting zone when practical.

For example:

Power Supply

↓

10m Cable

↓

Underwater Lights

A shorter cable generally means lower resistance and lower voltage drop.

Step 5 — Use Multiple Power Supplies

For a large fountain, one centralized power supply may not always be the best solution.

Imagine a project with:

100 × 10W DC24V underwater lights

Total load:

1000W

At 24V:

1000W ÷ 24V ≈ 41.7A

Trying to distribute more than 40A over very long DC24V cable runs can create significant voltage-drop and cable-sizing challenges.

A better approach may be to divide the project into several zones.

For example:

Zone A

25 lights

Zone B

25 lights

Zone C

25 lights

Zone D

25 lights

Each zone can have appropriately sized power distribution.

This can reduce cable length and simplify maintenance.

Centralized vs Distributed Power Supply

There are two common approaches for DC24V underwater lighting.

Centralized Power Supply

All power supplies are installed in one electrical cabinet.

Advantages

• Centralized maintenance

• Easy system management

• Simple power control

Disadvantages

• Longer DC cable runs

• Higher voltage-drop risk

• Larger cables may be required

Distributed Power Supply

Power supplies are installed closer to different fountain zones.

Advantages

• Shorter DC cable runs

• Lower voltage drop

• Easier circuit distribution

• Better for large projects

Disadvantages

• More installation locations

• More equipment to manage

• Each location requires suitable environmental protection

For large commercial fountain projects, distributed power can be worth considering.

Step 6 — Divide Underwater Lights into Circuits

Another effective method is to divide the fixtures into smaller circuits.

Instead of:

One Power Supply → 40 Lights

consider:

Circuit A → 10 Lights

Circuit B → 10 Lights

Circuit C → 10 Lights

Circuit D → 10 Lights

This reduces the current carried by each individual circuit.

It also makes troubleshooting easier.

If one circuit has a problem, the entire fountain does not necessarily have to be switched off.

Why Circuit Design Matters for RGB Underwater Lights

RGB underwater lighting is particularly sensitive to visual inconsistencies.

Imagine 30 RGB lights installed along a fountain.

If the power distribution is not balanced:

Lights 1–10

may appear brighter.

while:

Lights 21–30

may appear darker.

The result is an uneven color gradient.

For a professional fountain, this can reduce the quality of the entire lighting effect.

Therefore, for RGB projects, it is important to consider:

Power Distribution + Cable Size + Fixture Position + DMX512 Addressing

as one integrated system.

DMX512 Does Not Solve Voltage Drop

This is a common misunderstanding.

DMX512 is a control protocol.

DC24V is the power supply voltage.

They have different functions.

DC24V

Provides power to the underwater fixture.

DMX512

Controls:

• RGB color

• Brightness

• Scenes

• Color transitions

• Dynamic effects

Therefore:

DMX512 cannot compensate for insufficient DC24V power at the fixture.

A good fountain system needs both:

Stable Power

Reliable Control

How to Reduce Voltage Drop in DMX512 RGB Fountain Lighting

For a professional RGB fountain project, consider the following structure:

AC Input

↓

DC24V Power Supply

↓

Power Distribution

↓

RGB Underwater Lights

and separately:

DMX512 Controller

↓

DMX Signal

↓

RGB Underwater Lights

The power and control wiring should be designed according to the fixture manufacturer's requirements.

For large projects, separate power zones can be combined with DMX512 fixture grouping.

This allows the lighting designer to create:

• Color gradients

• Chasing effects

• Zone control

• Center-to-outside effects

• Music-synchronized scenes

while maintaining appropriate power distribution.

 Use a Star or Distributed Power Layout

For some fountain projects, a distributed or star-style power layout can be more effective than simply connecting all fixtures in one long chain.

For example:

Poor Approach

Power Supply → Light 1 → Light 2 → Light 3 → Light 4 → ... → Light 30

The current and cable resistance can create increasing voltage-drop concerns toward the end of the circuit.

Distributed Approach

Power Supply

↙ ↓ ↓ ↘

Zone A / Zone B / Zone C / Zone D

Each zone has a more manageable cable length and load.

The exact wiring topology should follow the fixture manufacturer's requirements and applicable electrical codes.

Do Not Increase DC24V Voltage Without Manufacturer Approval

When voltage drop occurs, some installers may consider increasing the supply voltage.

For example:

24V → 26V

This should not be treated as a general solution.

If the underwater light is designed for DC24V, supplying a voltage outside its specified range can damage the fixture or reduce its service life.

The correct solution is normally to improve:

• Cable size

• Cable length

• Power distribution

• Circuit design

• Power-supply location

rather than simply increasing the voltage.

Fluke also notes that excessive voltage drop in low-voltage systems is better addressed through lower-resistance conductors and connections rather than simply raising the supply voltage beyond the load's specified voltage.

Use High-Quality Connectors and Waterproof Connections

Cable resistance is not the only source of voltage drop.

Connections also have resistance.

Poor-quality:

• Connectors

• Terminals

• Junction boxes

• Cable joints

• Crimp connections

can introduce additional resistance.

For underwater lighting, connections also need appropriate waterproofing.

Therefore, use components that are suitable for the environment and follow the manufacturer's installation instructions.

A professional system should minimize both:

Cable Resistance

and

Connection Resistance

Check Voltage at the Farthest Underwater Light

Do not only measure the voltage at the power supply.

For a long DC24V lighting system, it is useful to check the voltage at the farthest fixture or the end of each circuit under representative operating conditions.

For example:

Power Supply

24.2V

Near Fixture

24.0V

Middle Fixture

23.4V

Far Fixture

22.3V

The actual acceptable voltage should be compared with the fixture manufacturer's specified operating range.

This is much more useful than checking only whether the power supply displays "24V."

Example — Reducing Voltage Drop in a Fountain Project

Suppose a project uses:

30 × 15W DC24V underwater lights

Total Power

30 × 15W = 450W

Current

450W ÷ 24V = 18.75A

The original design is:

One power supply → 40m cable → all 30 lights

This may create substantial voltage-drop concerns.

A redesigned system could be:

Power Supply

↓

Zone A — 10 lights

Zone B — 10 lights

Zone C — 10 lights

The system now distributes the load among multiple circuits.

The exact cable size and power-supply configuration should be calculated based on actual cable resistance, circuit length and fixture specifications.

Common Voltage Drop Problems and Solutions

Recommended Voltage Drop Design Process

For a professional project, use this process:

Step 1

Determine the number of underwater lights.

Step 2

Confirm the rated wattage of each fixture.

Step 3

Calculate total power.

Step 4

Calculate total current at DC24V.

Step 5

Determine cable length for each circuit.

Step 6

Select cable cross-section based on current and voltage-drop requirements.

Step 7

Divide the project into suitable power zones.

Step 8

Select appropriately rated power supplies.

Step 9

Check voltage at the farthest fixtures.

Step 10

Test the system at maximum intended lighting load.

This process is especially important for large RGB/RGBW fountain lighting projects.

What Voltage Drop Should You Allow?

There is no single universal percentage that applies to every DC24V underwater light.

The acceptable voltage drop should be determined from:

• Fixture manufacturer's operating-voltage range

• Project specifications

• Cable design

• Local electrical requirements

• Required lighting uniformity

A commonly used preliminary design target for low-voltage lighting may be around 3%, but this should not be treated as a universal requirement. Some projects may specify a different limit. Fluke provides 3% as a common corrective-action reference for certain circuit applications, but the appropriate limit depends on the actual system.

For a DC24V system:

3% of 24V = 0.72V

So a 3% design target would correspond to approximately:

24V − 0.72V = 23.28V

Again, the fixture manufacturer's specified operating range should take priority.

DC24V Underwater Light Cable Design Checklist

Before installation, check:

Electrical

• Rated fixture wattage

• Total load

• Operating current

• Power-supply capacity

Cable

• Cable length

• Cable cross-section

• Current capacity

• Voltage drop

• Temperature rating

Underwater Environment

• Waterproof cable

• Waterproof connectors

• Cable glands

• Junction boxes

• Corrosion resistance

Control

• RGB / RGBW

• DMX512

• Controller

• DMX addressing

• Signal distribution

Installation

• Power-supply location

• Circuit layout

• Maintenance access

• Local electrical regulations

IEC 60598-2-18:2022 specifically addresses fixed luminaires used in or in contact with water and includes requirements relating to external/internal wiring and waterproof cable options.

DC24V Underwater Lighting for Fountain Projects

Voltage-drop management is particularly important for:

• Hotel fountains

• Resort water features

• Commercial plazas

• Landscape ponds

• Musical fountains

• Architectural water features

• Large swimming pools

• Public landscape projects

These projects often contain many fixtures distributed over a large area.

A good design combines:

DC24V

IP68 Underwater Lights

Correct Cable Size

Distributed Power

RGB/RGBW

DMX512

This creates a more stable and flexible lighting system.

Always Lighting DC24V Underwater Light Solutions

Always Lighting provides LED lighting solutions for architectural and landscape applications, including DC24V underwater lighting for water features and fountain projects.

Depending on project requirements, underwater lights can be configured with:

• DC24V

• IP68

• RGB

• RGBW

• DMX512

• Stainless Steel Housing

• Different wattages

• Different beam angles

• Custom cable lengths

For a professional project, customers can provide:

Number of fixtures + fixture wattage + cable length + water depth + beam angle + RGB/RGBW + DMX512 requirement.

This information helps the lighting supplier evaluate the appropriate power-distribution approach.

Conclusion

Reducing voltage drop is one of the most important steps when designing a DC24V underwater lighting system.

The key principles are:

1. Calculate the total load

2. Calculate the current

3. Use appropriate cable sizes

4. Keep DC cable runs practical

5. Divide large systems into multiple circuits

6. Consider distributed power supplies

7. Use reliable waterproof connections

8. Check voltage at the farthest fixtures

9. Do not increase voltage beyond the fixture specification

10. Design power and DMX512 control systems together

For small water features, voltage drop may be relatively easy to manage.

For large fountains and commercial landscape projects, however, cable sizing and power distribution should be considered from the beginning of the lighting design.

A well-designed system can help maintain consistent brightness, stable RGB colors and reliable operation across the entire fountain.

FAQ

What causes voltage drop in DC24V underwater lights?

The main causes are cable resistance, long cable runs, high current, undersized conductors and resistance at connections.

Why is voltage drop more serious with DC24V?

A DC24V system requires more current than a higher-voltage system for the same power. Higher current makes cable resistance more significant.

How can I reduce voltage drop in DC24V underwater lighting?

Use larger cables, shorten cable runs, divide the system into multiple circuits and position power supplies appropriately.

Does a larger cable reduce voltage drop?

Generally, yes. A larger conductor has lower resistance and can reduce voltage drop, provided it is correctly selected for the installation.

Can I increase the power supply voltage to compensate for voltage drop?

Not unless the fixture manufacturer specifically allows it. A DC24V fixture should normally receive the voltage within its specified operating range.

Does DMX512 solve voltage drop?

No. DMX512 controls the fixture; it does not provide the fixture's electrical power.

How do I calculate DC24V voltage drop?

A simplified approach is:

Voltage Drop = Current × Total Circuit Resistance

The total resistance should include the complete cable path and relevant connections.

How do I calculate current for DC24V underwater lights?

Use:

Current = Total Power ÷ 24V

For example, 240W of lighting requires approximately 10A at 24V.

Should I use one power supply for a large fountain?

Not necessarily. Large fountains may benefit from multiple power supplies and distributed power circuits to reduce cable length and voltage drop.

Does cable length affect RGB underwater lights?

Yes. Long DC24V cable runs can cause voltage differences between fixtures, potentially affecting brightness and color consistency.

What voltage drop percentage should I use?

There is no universal value. A 3% target is sometimes used as a preliminary design reference, but the actual acceptable value should be based on the fixture specifications, project requirements and local regulations.

Is IP68 enough for an underwater lighting system?

No. IP68 addresses ingress protection under specified test conditions. The complete system should also consider electrical safety, cable construction, connectors, power supply and applicable standards. IEC 60598-2-18:2022 covers fixed luminaires for swimming pools, fountains and similar water applications.

Related product

https://www.always-lighting.com/led-underwater-light/dc24v-underwater-light/