The invention of the modern electric fuse is generally attributed to Thomas Edison. Around 1880 he and his team were the source of many of todays standard electrical products. As his electrical ideas came to fruition many products we now take for granted had to be perfected. The device we simply call a fuse is one of these inventions.

Basically a fuse is a safety device that stops the flow of electricity if an electrical limit is surpassed. In this way the amount of electricity is never allowed to exceed this preset limit.

Most people think the fuse protects the electrical device being used. Actually the primary purpose of the fuse is to protect the wiring that runs through the walls of your home. Without the fuse the wiring could overheat, causing the wood in the walls to become warm, and eventually cause a fire. The fuse is the first line of defense in the protection of your home and family.

Although circuit breakers are now the predominant electrical safety device for new homes, the fuse still has its place. Most household fuses are either "P" type or "D" type. This is easily confirmed by the capital letter stamped onto the top of the fuse. The P means PLUG and the D means DELAY.

Fuses come in many different sizes and shapes. The most common type used in homes is still the plug fuse. It has a cylindrical glass body, with a threaded metal base that allows it to be screwed into a matching fuse holder in your appliance or fuse box. At its tip is a metal contact through which the electricity flows once contact with the fuse box is made.

At the heart of its simplicity is the fact that once it blows it must be manually replaced. This forces the homeowner to question why the fuse failed. The answer is usually because of a failure of something within that particular circuit.

Inside every fuse is a soft metal link (usually lead) through which the electricity flows. The link is calibrated to disintegrate if the fuses maximum rating is exceeded. It can either blow because of too much electricity passing through it, or because it became overheated.

Fuses are rated in amperes. It is a measurement of electrical flow. The higher the amperage rating the more electricity can flow through it before the fuse blows. For 90% of your household electrical circuits the maximum allowable fuse is 15 Amps. The exceptions to this rule are your dryer, range, and hot water tank. They are higher amperage because they are specially wired to safely surpass the standard 15 Amp limit.

Never replace a fuse with one of a higher rating. Never replace a fuse with any other material or device. We have all heard horror stories of people replacing fuses with coins, pieces of metal, or bottle caps. Anyone who does this is placing no value on their own life, or that of their family.

If unsure of fuse amperage remove it and look for a number stamped on it. Look for a number stamped at the tip of the threaded portion of the fuse. Or look for a number printed on top of the glass section of the fuse. Lastly, look for a number printed on the paper label inside the fuse. If all else fails make note of the color of the paper label inside the fuse. Each different size of fuse has a specific color of label. The label inside a 15 Amp fuse is always blue, 20 Amp is brownish orange, 25 Amp is red, and a 30 Amp is green.

A plug fuse is the type generally seen in your electric range. In a range there is usually two 30A fuses for the oven, two 20A fuses for the right elements, two 20A fuses for the left elements, and one 15A fuse for the outlet.

The delay fuse is the other type of which consumers should be aware. It is used for special circumstances. It is used for electrical devices that require high starting amperage. Examples might be a power saw, furnace motor, or sump pump. One of the most common uses of a delay type fuse is when using a window air conditioner.

An air conditioner may require 40 or 50 amps of electricity during the first few seconds that it starts. If a plug fuse were used it would probably blow as soon as the air conditioner started. The delay fuse though solves this problem because if allows high amperage for a few seconds.

Once it starts the air conditioners amperage should fall back to less than 10amps. If not, after the first few seconds the delay fuse will operate like a standard plug fuse and blow. In this way a delay fuse can allow momentary high amperage while still protecting the household wiring.

The disadvantage of delay fuses is that they are much more expensive. Therefore, only purchase when absolutely necessary, or when required for special appliances such as a window air conditioner.