What are the ATO/ATC blade fuse colour codes?
ATO/ATC blade fuses are made in the 1-40 A range and the body colour indicates the current rating: black 1 A, grey 2 A, violet 3 A, pink 4 A, tan 5 A, brown 7.5 A, red 10 A, blue 15 A, yellow 20 A, clear 25 A, green 30 A, blue-green 35 A, orange 40 A. The colour is for quick identification; also verify the rating from the number on the body.
The colour code was standardised so that the right rating can be picked in seconds from a panel holding dozens of fuses in a box. The full list:
- Black 1 A, grey 2 A, violet 3 A, pink 4 A, tan 5 A
- Brown 7.5 A, red 10 A, blue 15 A, yellow 20 A
- Clear 25 A, green 30 A, blue-green 35 A, orange 40 A
Points to watch in practice:
- The shade of colour can vary slightly between manufacturers and can fade on an aged fuse. The definitive information is the number moulded on the body.
- ATO and ATC are the same size; ATC has a closed body while the top of the ATO is open. The closed type is preferred in damp environments.
- Mini, standard and maxi are different bodies; the same colour is used in different sizes too, so choose the size that fits the holder.
- For currents above 40 A, larger-bodied types or a circuit breaker are used instead of a blade fuse.
When keeping spares, put one of every rating in the installation and, if possible, a fuse puller in the vehicle. Replace a blown fuse with the same rating; if the colour does not match, read the rating first.
The full topic: Installation, redundancy and field continuity