Keyboards have two USB cables because one cable cannot supply enough power for all the features. The main cable sends your keystrokes to the computer and draws power. The second cable, often labeled "Power" or "USB," provides extra electricity for RGB lighting, USB pass-through ports, and other power-hungry features. Without both cables connected, some features will not work or will run at lower settings.

The two cables work as a team: The primary cable handles HID communication (your typing) plus up to 500mA of power. The secondary cable adds another 500mA to 900mA dedicated to RGB controller chips, pass-through ports, and display screens. Both cables connect to different USB ports on your computer to avoid overloading a single connection.

How Much Power Does a USB Port Provide?

A standard USB 2.0 port delivers 500 milliamps (mA) at 5 volts, which equals about 2.5 watts of power. According to the USB Implementers Forum specifications, this is the maximum a single USB 2.0 device can draw. A basic keyboard without lights or extra features uses only about 100mA to 200mA. However, modern gaming keyboards with full RGB lighting can need 800mA to 1,000mA or more, which is double what one USB port can deliver.

What Uses All That Power?

  • RGB LED Lighting: Each LED can use 20mA to 50mA. On a full-size keyboard with 104 keys, that adds up to over 1,000mA when all lights shine at full brightness.
  • USB Pass-Through Ports: If your keyboard has a USB port built into it for plugging in a mouse or flash drive, that port needs its own power supply, typically another 500mA.
  • OLED or LCD Screens: Some keyboards include small display screens that show system stats or custom images. These screens draw 100mA to 300mA continuously.
  • Onboard Memory: Keyboards that store lighting profiles or macros internally need extra power for flash memory chips.

What Is USB Pass-Through and Why Does It Need a Second Cable?

USB pass-through is a feature where your keyboard has one or more USB ports built into it. You can plug a mouse, headset, or thumb drive directly into the keyboard instead of reaching around to your computer. This saves desk space and keeps cables organized.

The pass-through port acts like a tiny USB hub inside your keyboard. According to USB specifications, a hub needs its own power source to supply connected devices. Without the second cable, the pass-through port either will not work at all or will not provide enough power to charge devices or run high-power accessories.

Do I Need to Connect Both USB Cables?

It depends on which features you use. For basic typing and shortcuts, one cable works fine. The keyboard will function as an input device without any problems. However, if you want the full experience your keyboard was designed for, plug in both cables.

What You Lose with Only One Cable

  • Dimmer RGB Lights: The keyboard limits brightness to about 30% to 40% to stay within the single port's power limit.
  • No USB Pass-Through: Any built-in USB ports will not recognize connected devices.
  • Slower Response Time: Some keyboards drop their polling rate, meaning there is a slightly longer delay between pressing a key and the computer registering it. This matters most for gaming.
  • Macro Problems: Complex macros that play back rapidly may fail during lighting effects because both need power at the same time.

Tip: If you are short on USB ports, connect the main data cable first. Your keyboard will still work for typing. You can always add the second cable later when a port becomes available.

How to Connect a Dual USB Keyboard Properly

Most dual USB keyboards label their cables clearly. Look for text printed on the cable or connector that says "Keyboard," "Data," "Power," or "USB Hub." The setup takes just a few steps.

Step by Step Setup

  • Connect the Primary Cable First: Plug the cable labeled "Data" or "Keyboard" into any USB port on your computer. This cable is required.
  • Add the Secondary Cable: Plug the cable labeled "Power" or "USB" into a different USB port. Do not use the same port or the same USB hub.
  • Use Motherboard Ports When Possible: The USB ports on the back of a desktop computer connect directly to the motherboard and usually deliver more stable power than front panel ports.
  • Avoid Daisy-Chaining Through Hubs: Plugging both cables into an unpowered USB hub can cause power problems. If you must use a hub, choose a powered hub with its own wall adapter.

Troubleshooting Common Dual USB Problems

If your keyboard's features are not working correctly after connecting both cables, there are a few common causes and fixes.

  • RGB Flickering or Turning Off: Both cables may be plugged into ports on the same USB controller. Try moving one cable to a different group of ports, such as from front to back.
  • Pass-Through Port Not Working: Make sure the second cable is connected and recognized. Check Windows Device Manager for a "USB Composite Device" or "USB Hub" entry.
  • Random Disconnects: Disable USB selective suspend in Windows power settings. This feature cuts power to USB devices to save energy, but it can cause problems with high-power keyboards.
  • Keyboard Not Detected: Install the keyboard's software or drivers before connecting the second cable. Some keyboards need specific software to enable dual USB mode.

Important: If you see Windows error messages about "power surge on USB port" or "USB device not recognized," disconnect both cables immediately. This usually means there is a cable problem, a faulty port, or your power supply cannot handle the load.

Will USB-C Keyboards Still Need Two Cables?

USB-C and USB 3.1 ports can deliver more power than older USB 2.0 ports. A USB-C port following the USB Power Delivery specification can provide up to 15 watts (3 amps at 5 volts) through a single cable. This is enough for most RGB keyboards without needing a second connection. As USB-C becomes more common on both keyboards and computers, the need for dual cables is slowly going away. However, many current gaming keyboards still use USB-A connectors, which follow the older power limits.

Which Keyboards Use Dual USB Cables?

Dual USB setups appear mainly on premium gaming keyboards and productivity keyboards with extra features. Budget keyboards and most wireless keyboards use a single cable or receiver. If you see two cables coming from a keyboard, expect it to include at least one of these features: per-key RGB lighting, USB pass-through ports, an OLED display, or an audio pass-through jack.

Quick check: Look at the keyboard's packaging or product page. If it lists features like "USB pass-through," "per-key RGB," or "OLED display," it probably uses two USB cables. The specs should also show total power draw in milliamps.