How do you read a fuse marking?

The first letter(s) (TT, T, M, F, FF) tell you what type of fuse it is:

1. FF = Fast Fast. Very Quick Acting. ( also known as Anti Surge)
2. F = Fast. Quick Acting. ( also known as Anti Surge)
3. M = Medium. “Normal” or Very Short Delay.
4. T = Time. Time Delay or Slow Blow.
5. TT = Time Time. Long Time Delay or Very Slow Blow.

What do the numbers on a fuse mean?

Car fuses are color coded by amp rating. For example, a standard blue fuse has a 15-amp rating, yellow is 20 amps and green is 30. You can buy them at any auto parts store and at well-stocked service stations. Note: If your new fuse blows soon after installing it, you could have problems in that circuit.

What does the T stand for on a fuse?

T = slow burn fuse. F = fast acting fuse. TT = very slow burn fuse. FF = very fast acting fuse.

What is the fusing current?

Fusing current is the current required to melt the wire which is inside the fuse. If you see a fuse, inside that there will be a wire. That wire or fuse will have some limited rating of current. That fuse can withstand only till its rating current flow.

What are the speed markings on a fuse element?

Fuse Element Speed Markings Table 2. Fuse Breaking Capacity Markings Note: Many small cartridge fuses will have additional markings stamped on the end caps. These are usually either; a series number, a part number, or product approval markings (refer table 3 below).

How do I identify a fuse?

These are usually either; a series number, a part number, or product approval markings (refer table 3 below). If you are unable to identify the fuse, please contact us. Table 3. Quality & Approval Markings on the fuse cap

What do the markings on fuse caps mean?

Fuse Breaking Capacity Markings Note: Many small cartridge fuses will have additional markings stamped on the end caps. These are usually either; a series number, a part number, or product approval markings (refer table 3 below). If you are unable to identify the fuse, please contact us.

What is PolySwitch and poly-fuse?

Littelfuse PolySwitch and POLY-FUSE devices are Polymeric Positive Temperature Coefficient (PPTC) devices which offer a resettable overcurrent protection alternative, thereby reducing warranty, service and repair costs.