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Cable Drums and Reels: Ratings, Heat and Choosing the Right One
Why a coiled extension reel is rated lower than an uncoiled one, what the ratings on the drum mean, and how to pick between 13A, 16A and 32A.
~6 min read · Updated August 2026 · By the Stage Supply team
In this guide:Coiled ratings · Ratings · Choosing · Speaker cable drums · Picks · FAQ
A cable drum looks like the simplest thing in the truck and it is the item most often used outside its rating. The reason is a piece of physics that is not obvious: the same cable carries less current when it is wound on the drum than when it is run out.
That is why extension reels carry two ratings on the label, and why the lower one is the one that applies most of the time on an event.
Why a coiled reel is rated lower
Current flowing through a conductor generates heat. A cable run out along the floor loses that heat to the air along its whole length. The same cable wound in layers on a drum is insulating itself, and the inner turns have nowhere to dump their heat.
The result is that a reel rated at, say, 13A fully unwound may be rated at only a few amps while wound. Exceed that and the insulation softens, then fails, and the failure is inside the drum where nobody can see it.
The habit worth forming
Run the reel out fully before drawing any significant load through it, even if you only need three metres. If you cannot run it out, treat the coiled rating as the real one.
Reading the ratings
| Type | Typical connector | Common use | Watch for |
|---|---|---|---|
| 13A extension reel | 13A BS1363 | Small tools, small loads, domestic style | Very low coiled rating, thermal cutout |
| 16A reel | Blue 16A CEEform | Standard event power runs | Cable size, not just connector rating |
| 32A reel | Blue or red 32A CEEform | Distribution to a distro | Weight, and cable cross section |
| Empty reel | None, you fit the cable | Making a run to a specific length | Fit cable of the correct rating |
The connector rating and the cable rating are two different things, and they must both be adequate. A 16A connector on undersized cable is a 16A connector on undersized cable, not a 16A extension.
Many reels have a thermal cutout that trips when the drum overheats. That is a last line of defence, not a working method: if the cutout is tripping, the reel is being used wrongly.
Choosing a reel for events
- Match the reel to the load you will actually draw, not to what the socket can supply.
- Prefer CEEform connectors over 13A for anything on a stage. They lock, they are IP rated, and they are the site convention.
- Buy rubber-sheathed cable, usually H07RN-F, for anything that goes on the floor. PVC extension leads are for offices.
- Consider empty reels and make up your own lengths, which gives you the right cable, the right connectors and the right length.
- Label the length on the drum. Not knowing the length is how runs end up two metres short.
Speaker and signal cable on drums
Drums are also how bulk speaker and installation cable is bought and stored, and the same physics does not apply in the same way because signal and speaker levels carry far less current.
What does matter there is cable specification. Speaker cable is chosen by conductor size for the run length and the impedance, and installation cable often needs to be LSZH, meaning low smoke and zero halogen, for use in public buildings. Buying the right specification off the drum matters more than the drum itself.
Cable care, coiling and storage is covered in looking after your cables.
Popular picks from the shop
Frequently asked questions
Why do extension reels have two current ratings?
One for fully unwound and one for wound. Coiled cable cannot shed heat, so its safe current is much lower. The wound rating is the one that applies if you do not run the reel out.
What happens if I overload a coiled reel?
It heats up from the inside, the insulation degrades and can eventually fail. Many reels have a thermal cutout that trips first, which is a warning rather than a normal operating condition.
What cable should an event extension use?
Rubber-sheathed flexible cable, commonly H07RN-F, sized for the load and the length. It survives being walked on, rolled over and rained on in a way that PVC does not.
What does LSZH mean?
Low smoke and zero halogen. In a fire the cable produces less smoke and no halogen gases, which is why it is specified for installations in public buildings and escape routes.
