Here’s What Time Delay Fuses Can Do for Your Circuits

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Time delay fuses allow the initial power surge without destroying the circuit. You may need it more than you think.

The fuse, in electronics, protects electrical circuits in the event of excessive current. If overcurrent occurs, it will heat up until it melts and breaks the circuit. During such overload conditions, though, the fuse tends to blow – and it needs all the time it can get to avert this.

This is where the time delay fuses come into play. It is a special kind of fuse that allows an electrical surge for a short time before it gets blown. Their working principles work wonders for your circuits, so read on to learn more about them.

‘Fuse’ in Electrical Engineering Explained

A fuse is a safety device in an electric circuit. It keeps the wiring and appliance safe in case of a surge current.

For it to work efficiently, it must contain a fusing element capable of melting. This metal strip-made piece is usually sealed inside a glass fuse body. When there is a fault, the wire melts, enabling the electricity flow to stop.

Fuses come in two common types. Each category differs from the other when it comes to the functions and timely response, and these are:

• Time delay fuses (with a label that reads “T” or “S”)
• Fast-acting fuses (“F”)

Fast-acting fuses give a quick response to electric spikes. By breaking the circuit, they can offer protection to the devices. But they cannot withstand temporary overloads, unlike time delays.

Time Delay Fuses

Some electrical devices need a high inrush of current to function. Time delay fuses, also known as slow blow fuses, can sustain that kind of overload but only for a limited period.

Nonetheless, they allow an initial power surge without destroying the circuit. This makes them an integral part of systems that use a high inrush of inductive load. Standard fuses are often useless in this case; for one, they do not allow any power surge beyond their amp rating.

Another way to put it is they allow for a temporary current surge without going above the fuse’s current rating. And because of this, time delay fuses are popular and common in motor circuits. They bear high currents to flow through when the motor needs to start and speed up. The circuit is left unharmed.

It is no wonder why almost all types of fuses come in time delay versions. Popular ratings include 15 amp time delay fuses, 30 amp, 50 amp, and 100 amp, to name a few.

How do time delay fuses work?

Regular and time delay fuses feature the same design, but their functions vary. Standard models are common in circuits and appliances. The more exposure they get to electrical current than they are rated for, they will burn out. The only way for them to protect devices and power lines from damage is to break the circuit.

A time delay fuse, in contrast, can handle 100% – 200% more electrical current than the regular type. Besides the outburn link, there is a short connector with a spring attached to it – soldered onto the fuse wire. It is what makes a time-delay fuse bear over the normal load.

It works by letting electrical surges (below the breaking capacity) pass through. It will blow out if the electricity crosses that maximum point. If the overload remains for a long time, this will cause the solder joint to melt. The spring will then be released and open the contact. As a result, the fuse wire will melt, the same case for the standard unit.

Types of Time Delay Fuse

There are different types of time delay fuses, and each variation has its own purpose. You must know the load of the circuit before selecting a fuse for an application.

Class CC

A Class CC type delays the time for at least 12 seconds at 200% of the rated current. It offers close sizing on relay circuits and small motors. Plus, it gives the highest protection for components with short-circuit current rating. Best used in specialised and branch circuits, street lighting, and more.

Midget fuses

Like Class CC, midget fuses also provide a 12-second time delay. They appear in a tube-like dual-element form of construction.

One works by allowing the surges to pass through from one end to another without affecting the fuse wire. Best used in solenoids, transformers, small motors, and high-inrush circuits.

Class J and R

For this type, they delay the time less than the previous two, with at least 10 seconds but at 500% of the rated current. Class J and R are high-performance fuses and capable of repeated cycling.

Suitable for all high-inrush loads, such as transformers, motor branches, and lighting circuits. You will also find them in the following:

• IEC-style motor contactors and starters
• Circuit breakers with lower interrupting ratings

Other variations in the time-delay category include Class L, Time Lag, and Class RK5.

Common Applications

A time delay fuse is more tolerant to overcurrent strikes, which makes it a safer alternative. Ideal for appliances that draw power in excess during the startup, including in:

Motors

An electrical motor takes a higher volume of electricity to start operation. A regular fuse, in this case, will blow out at the beginning and cut the circuit. But a slow blow fuse will initiate the power surge while protecting the circuit from overload.

Fluorescent lamps

A fluorescent lamp also consumes much more power when switched on. But this decreases over time when left on, making a slow blow fuse beneficial in such a case. For one, it can protect the light’s vulnerable circuitry from the opening spike.

Note: Fuses are engineered for specific applications. No regular fuse can swap its place inside a receptacle and vice versa.

Get Your Time Delay Fuses Here!

We offer a wide range of Cartridge Fuses, available in time-delay versions. Perfect for protecting power lines and electrical equipment from overloads and short circuits.

Time Delay Fuses 3AG

A miniature glass electronic fuse with a diameter of 0.25 inches and a length of 1-1/4 inches. Fuse ratings are provided at both 125 and 250 volts AC.

M205 Time Delay Fuses

A glass-type M205 fuse that has a time delay action with a 250V rating. It provides protection to devices or internal circuits from short circuits and overcurrent.

Available current rating: 1A to 10A; 100mA to 800mA.

The Bottom Line

Fuses play a crucial role in electrical systems. They offer protection both to the circuit and the user from electrocution and fire. But if more power is being drawn than should be, the fuse blows and can result in a dead circuit.

In this case, a time delay fuse can make a difference. It allows the surge in electricity for a short time before the fuse burns and blows out. But most of the time, it aims to bear overloads without blowing. Thus, making it more beneficial and a lot safer for certain types of appliances.