Table of Contents

- 1 How do you calculate the value of a fuse?
- 2 How do you determine the size of a fuse in a circuit?
- 3 What is the current rating of a fuse?
- 4 How do I choose the right size fuse?
- 5 What fuse ratings are there?
- 6 How do you read fuse numbers?
- 7 What is the working principle of a fuse?
- 8 How is the fuse rating of a motor calculated?

## How do you calculate the value of a fuse?

The fuse rating can be calculated by dividing the power used by the appliance by the voltage going into the appliance. I (Amps) = P (Watts) ÷ V (Voltage).

### How do you determine the size of a fuse in a circuit?

Find the size of fuse by multiplying the amps required by the device (2) by 1.5. 2×1.25 = 2.5 then we will round up to the nearest fuse size (in multiples of 5 amps) which would call for a 5 amp fuse. Cross Reference that fuse size to verify that it’s below the Maximum fuse size called out by this chart.

**What are fuse values?**

Fuses come in standard ratings of 3 A, 5 A or 13 A. The best fuse to use in this example would be the 13A fuse. The 3A and 5A fuses would blow even when the fire was working normally.

**What is a fuse measured in?**

amperes

The ampere rating is almost always shown on the fuse and is usually expressed in amperes (eg. 10A or 0.5A), but it could also be expressed in milliamps (eg. 100mA). Sometimes the ampere rating is incorporated into the fuse part number eg.

## What is the current rating of a fuse?

The current rating is the maximum current that can flow through the fuse under normal conditions. Fuses will typically be de-rated at 25% to avoid nuisance blowing at 25˚C. An example from an article titled “Fuseology” by Littelfuse goes on to use a 10 amp fuse for a 7.5 amp circuit at 25˚C.

### How do I choose the right size fuse?

Always select a fuse size to protect the wire according to its rating. In some cases, a product manufacturer will specify a fuse value and it will usually be lower than that required for protecting the wire. If this fuse value is too high to protect the wire, use a bigger wire in the circuit.

**How do I choose a fuse size?**

In order to select the right amperage of the fuse, you first need to know the full-load steady-state current of the circuit at an ambient temperature of 25º C (68º F). Once the current value is determined, then a fuse rating should be selected as to be 135% of this value (taken to the next standard value).

**What is fuse voltage rating?**

The voltage rating of a fuse is a function of its capability to open a circuit under an overcurrent condition. Specifically, the voltage rating determines the ability of the fuse to suppress the internal arcing that occurs after a fuse link melts and an arc is produced.

## What fuse ratings are there?

The standard voltage ratings used by fuse manufacturers for most small- dimension and midget fuses are 32, 63, 125, 250 and 600.

### How do you read fuse numbers?

As these fuses are larger in size, there is usually a lot more information printed on the fuse body. This information that is likely to be found on the fuse is summarised in the following table….Fuse Markings.

Marking | Fuse Element Speed |
---|---|

M | Medium Acting (Mitteltrage) |

T | Slow Acting (Trage) |

TT | Very Slow Acting (Trage Trage) |

**How to calculate the correct fuse size for your circuit?**

Calculate The Correct Fuse Size For Your Project. 1 Identify the load current in the circuit. See this guide to learn how to calculate load current. 2 Identify the smallest gauge wire the load current will flow through. 3 Enter values in the calculator below.

**Where do you find the fuse rating on a light?**

You’ll usually find the fuse rating on the side of your fuse, which will be given in amps. Fuse rating is the amount of current needed for the fuse to blow or break. When this happens, it stops the electrical power from flowing through the electrical circuit.

## What is the working principle of a fuse?

Electrical Fuse – The Working Principle. Electric current can flow through a conductor only when the circuit formed is complete. If there is a break in the loop, electric charges cannot flow through. This is also how switches operate.

### How is the fuse rating of a motor calculated?

A fuse for a machine is rated on the load that the machine carries when running. For example, a 1-HP (746W) motor operating at 115V would draw 746/115 = 6.5A at full load, so theoretically a 10A fuse would be sufficient. The starting (“inrush”) current is often many times the normal operating current.