Linking multiple linear high bays in a series simplifies wiring runs and saves time on large projects. This technical guide explains the correct procedure, load calculations, and best practices for safely and effectively daisy-chaining your fixtures. Following these steps ensures a reliable, code-compliant installation that performs efficiently for years.
Pre-Installation Planning and Load Calculation
Before running a single wire, proper planning is essential. A few minutes of calculation prevents hours of troubleshooting, ensures safety, and guarantees optimal performance. I’ve seen countless projects delayed because the initial circuit planning was rushed. Don’t make that mistake. Start here.
Calculating Total Load and Circuit Capacity
The first step is to determine the maximum number of fixtures your circuit can safely handle. This is governed by the National Electrical Code (NEC), which mandates that continuous loads (like lighting) should not exceed 80% of the circuit breaker's rating.
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Find the Fixture's Amperage: Check the spec sheet for the fixture's wattage at your operating voltage. Use the formula:
Amps = Watts / Volts. For example, a 150W fixture on a 120V circuit draws150W / 120V = 1.25A. -
Calculate Maximum Circuit Amperage: Apply the 80% rule. A 20-amp breaker can handle a continuous load of
20A * 0.80 = 16A. A 15-amp breaker can handle15A * 0.80 = 12A. -
Determine Maximum Fixtures: Divide the maximum circuit amperage by the fixture's amperage. For our example:
16A / 1.25A = 12.8. You must round down, so you can safely run 12 of these 150W fixtures on a 20A, 120V circuit.
Pro Tip: Always use the correct wire gauge for your circuit's ampacity. A common and safe practice is to use 14 AWG wire for 15A circuits and 12 AWG wire for 20A circuits. For very long runs on a 20A circuit, stepping up to 10 AWG wire is a wise investment to mitigate voltage drop.
Voltage Drop: The Silent Performance Killer
Voltage drop is the gradual loss of voltage along the length of a wire. While a small amount is normal, excessive drop can cause fixtures at the end of a long run to appear dimmer, flicker, or even fail prematurely. I once had to troubleshoot a dimming system that was behaving erratically; the issue wasn’t the expensive controller, but a 5% voltage drop at the end of the chain that was starving the drivers.
A professional heuristic is to keep voltage drop under 3% for the entire branch circuit. The higher your voltage, the lower the current, which in turn reduces voltage drop. This is why running fixtures at 277V is common in commercial settings—you can create much longer, stable runs with the same wire gauge compared to 120V.
Practical Limits: How Many Fixtures to Connect in a Series
Beyond the electrical load calculation, there are practical limits to a daisy-chain run. While a fixture may have input and output wires suggesting infinite connections, field experience shows that limiting a single run is best for reliability.
A common misconception is that you can keep adding lights as long as the circuit's amperage limit isn't exceeded. In reality, managing voltage drop and minimizing potential points of failure is more important.
General Field Guideline for Maximum Fixtures in a Single Run:
| Circuit Voltage | Breaker Rating | Recommended Max Fixtures per Run |
|---|---|---|
| 120V | 15A | 7-9 Fixtures |
| 120V | 20A | 10-12 Fixtures |
| 277V | 15A | 12-15+ Fixtures |
| 277V | 20A | 15-20+ Fixtures |
Note: These are experience-based guidelines assuming typical 100W-165W fixtures. Always perform your own load calculations as the primary source of truth. For a detailed guide on fixture placement, see our article on Spacing and Layout for Linear High Bay Mounting.
Step-by-Step Guide to Series Wiring
With your plan in place, you can begin the installation. This process assumes you are using fixtures designed for series wiring, such as the versatile Linear High Bay LED Lights -HPLH01 Series, which features a dedicated wiring access compartment.
Safety Disclaimer: This guide is for informational purposes only. Electrical work can be dangerous. Always de-energize circuits and follow all local electrical codes and safety regulations. If you are not qualified, hire a licensed electrician.
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Step 1: De-energize the Circuit: At the breaker panel, turn off the circuit you will be working on. Use a voltage tester to confirm there is no power at the junction box where you will start your run.
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Step 2: Mount the First Fixture: Securely mount the first linear high bay in the series. Run the main power feed (from the panel) to this fixture. Do not connect it yet.
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Step 3: Prepare Wires for Through-Connection: Open the wiring compartment on the fixture. You will typically find input wires (for power coming in) and a set of output or "through" wires (to send power to the next fixture). Pigtail connections—using short lengths of wire connected with wire nuts or push-in connectors—are a reliable method for joining wires within a junction box.
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Step 4: Make the Connections:
- Connect the incoming power feed (black for Line, white for Neutral, green for Ground) to the fixture's input wires.
- Connect a new length of cable (your "whip" to the next fixture) to the first fixture's output wires.
- Run this whip to the input of the second fixture. Repeat this process for all fixtures in the chain.
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Step 5: Secure and Inspect: Ensure all connections are tight and secure inside an approved junction box. Use strain relief fittings where cable enters the fixture to prevent stress on the electrical terminals. This is a key requirement for passing inspection and is a core principle of safe luminaire installation under standards like UL 1598.
Wiring for 0-10V Dimming in a Series
Most modern commercial high bays use 0-10V dimming. Wiring this correctly is critical; it's where many DIY and even some professional installations fail.
Understanding 0-10V Control Wires
0-10V dimming uses a pair of low-voltage control wires, typically one purple (or violet) for the positive (+) signal and one gray or pink for the negative (-) common reference. These wires carry a DC voltage from 0V to 10V from a compatible dimmer switch to the LED driver. The driver interprets this voltage to set the light output (e.g., 1V = 10% brightness, 10V = 100% brightness). For a full breakdown of terms, the NEMA LSD 64 - Lighting Controls Terminology guide is an excellent resource.
Best Practices for Dimming Control Runs
The most common mistake I see is installers treating the low-voltage dimming wires the same as the high-voltage power wires. The NEC requires low-voltage and high-voltage wiring to be kept separate unless the low-voltage cable is specifically rated for the higher voltage (Class 2 vs. Class 1).
- Do: Run the purple and gray wires from the dimmer switch to the first fixture. At each fixture, use a pigtail connection to connect the incoming control pair, the fixture's control wires, and the outgoing control pair to the next fixture. This creates a parallel control circuit.
- Don't: Run the control signal through the driver. Unlike power, which is designed to pass through, the 0-10V signal should be tapped at each fixture. Chaining it through the drivers can degrade the signal and cause unpredictable dimming behavior.
- Do: Maintain correct polarity (+ to +, - to -) throughout the entire run. A reversed connection can disable dimming for the entire chain.
Advanced Considerations and Compliance
For large-scale projects, a few advanced topics can make the difference between a smooth commissioning and a problematic one.
Inrush Current
When a large bank of LED fixtures (e.g., more than 12) is switched on simultaneously, the initial inrush of current to charge the drivers can sometimes be high enough to trip a standard breaker. If you experience this, the solutions are to either use breakers designed for high inrush current (HACR type), split the fixtures into smaller groups on separate circuits, or use a control system that can stage the startups by a few milliseconds.
Safety and Inspection Readiness
To ensure your installation is safe and will pass an electrical inspection, follow these final steps:
- Safety Cables: Always install a secondary safety cable for any suspended fixture. It’s a small cost that prevents a huge liability. Our Safety Cable Guide for Linear High Bay Installs provides detailed instructions.
- Label Everything: Label the circuit ID on both ends of the run and at the breaker panel. This is invaluable for future maintenance.
- Verify Certifications: Use official databases like the UL Solutions Product iQ Database to confirm that your fixtures are certified. This provides undeniable proof of safety compliance for inspectors and insurance providers.
Key Takeaways
Wiring linear high bay lights in a series is an efficient method when done correctly. The core principles for a successful project are to plan your electrical loads meticulously, respect the limits of voltage drop, physically separate power and control wiring, and build to a professional standard that prioritizes safety and serviceability. By grounding your work in these fundamentals, you create a lighting system that is not only fast to install but also robust and reliable.
Frequently Asked Questions (FAQ)
How many linear high bay lights can I put on a 20A circuit? This depends on the fixture wattage and circuit voltage. First, calculate the max continuous load (16A for a 20A circuit). Then divide that by your fixture's amperage (Watts / Volts). For example, you can run up to twelve 150W fixtures on a 120V circuit (16A / 1.25A per fixture).
What wire gauge should I use for high bay lights? For the circuit wiring, use 14 AWG for 15A circuits and 12 AWG for 20A circuits. For the whips between fixtures, you can often use 18 AWG if it's a standard offering with the fixture, as the load is only for a single unit. However, using 12 or 14 AWG consistently is a more robust practice.
Do I need a special dimmer for 0-10V LED fixtures? Yes, you must use a compatible 0-10V dimmer switch. A standard residential (TRIAC) dimmer will not work and can damage the LED driver.
Can I mix different wattage fixtures in the same series? Electrically, yes, as long as you calculate the total load correctly. However, for consistent lighting and dimming performance, it is highly recommended to use identical fixtures throughout a single daisy-chained run.
Why are my lights at the end of the chain dimmer than the others? This is a classic symptom of excessive voltage drop. The run is likely too long for the wire gauge and voltage used. You may need to shorten the run, split it into two, or use a thicker gauge wire to solve the problem.