"USB Accessories Disabled" on a Mac: the power problem behind it
· 5 min read
The notice reads “USB Accessories Disabled”, and under it: “Unplug the accessory using too much power to re-enable USB devices.” The Mac cut power to its USB ports because something connected asked for more than a port can safely give. Unplug everything, then plug accessories back one at a time to find the one responsible. Common culprits are portable drives with no power plug and hubs without an adapter, and a powered hub or the drive’s own power supply usually fixes it.
What the message means
Every USB port can supply a limited amount of power. When a device pulls more than that, or draws power in a way that looks like a short circuit, the Mac switches the port off to protect itself and the device. Engineers call this overcurrent protection. Nothing is broken by the notice itself: it’s the protection working.
Apple’s support page for this, If you see USB Devices Disabled on your Mac, uses slightly different wording but gives the same advice: disconnect and reconnect the device, try another port, and connect the device straight to the Mac instead of through a hub. If the hub is self-powered, check that its AC adapter is connected.
Related notices come from the same part of macOS and mean different things:
- “USB Accessory Needs Power” means the accessory isn’t getting enough power where it’s plugged in, such as a keyboard’s port or an unpowered hub. Its text asks you to connect the accessory “to power or a USB port on this Mac.”
- “Too many USB Accessories” says “You have exceeded the number of supported USB accessories.”
- “Too many USB Hubs” says “USB only supports 5 chained hubs.” Hubs are plugged into hubs too many levels deep.
If your accessory is asking permission instead, that is a different prompt, covered in Allow accessory to connect.
Find the accessory that caused it
- Unplug everything from the Mac’s USB and Thunderbolt ports, including hubs and docks.
- Check that USB devices work again with one known-good device, such as a mouse. If they don’t, restart the Mac with everything unplugged and try again.
- Plug in one accessory at a time, waiting a moment between each.
- When the notice returns, the last thing you plugged in is the cause, or it’s the pair of that device and its cable.
If it only appears with several things connected, the total is too much for the port or hub, and no single device is at fault.
The usual causes and their fixes
A bus-powered hard drive. Portable drives with no power plug take all their power from the port. Use the drive’s own power supply if it has one, or plug the drive into a powered hub.
A hub or dock without enough power. A hub with no AC adapter shares whatever the Mac gives it among everything attached. Plug in the hub’s adapter. A dock for a laptop that lives on a desk normally has its own supply for this reason.
A phone or tablet charging from a port. A phone charging through a hub adds to the load on that hub. Charge it from a wall adapter instead.
A damaged or poor cable. A damaged cable can cause the port to cut power. Swap in a different cable before blaming the device. If the port is USB-C, telling Thunderbolt, USB-C and USB4 ports apart and why a USB-C cable can charge but not carry video explain why cables that look identical behave differently.
A faulty accessory. If a device triggers the notice on its own, on several ports and with several cables, it has a fault. Stop using it.
When nothing is plugged in
The notice can still appear, and then there are a few things to look for:
- A hub or adapter is still attached, even if it looks empty. Check every port, including on a display.
- Dirt, lint or moisture is in the port. Look in with a flashlight. Don’t poke at it with metal; if you see liquid or debris you can’t blow out, stop and get service.
- The port itself is damaged, for example after a bent connector or a knock.
Restart once with every cable removed. If the notice returns with nothing connected at all, that is a hardware question for an Apple Store or authorized service provider, not something a setting will fix.
Don’t do this
- Don’t keep re-plugging a device that triggers it every time. Repeating it won’t clear the cause.
- Don’t buy a hub on price alone for bus-powered drives. A hub that comes with its own power adapter is the safer choice.
Questions
How do I re-enable USB devices on my Mac? Unplug the accessory using too much power, as the notice says. If you don’t know which one it is, unplug everything, then reconnect them one at a time. If the ports stay off, restart the Mac with everything unplugged.
Why does it say USB Accessories Disabled when nothing is plugged in? Usually something is still attached, such as a hub, adapter or display cable. Otherwise suspect debris or moisture in a port, or a damaged port. If it appears with nothing connected, have the Mac checked by service.
Can a USB accessory damage my Mac? The notice is the Mac’s protection switching the port off. A device or cable that trips it repeatedly is worth replacing, and one notice on its own doesn’t mean the Mac is harmed.
Does a powered hub fix it? Often, yes, when the cause is several bus-powered devices or a hungry drive. A powered hub supplies its own power rather than taking it from the Mac. It won’t help if a cable or device is faulty.