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Your Project Needs Circuit Protection

06 May, 2020 | Quest Components
 Your Project Needs Circuit Protection

Your Project Needs Circuit Protection

Circuit protection is important for any electrical installation or project. With a circuit protective device, a weak link is added to a circuit; this link is designed to be broken if a fault occurs, protecting the circuit from damage and/or projecting operators from injury.

Types of Circuit Protective Devices

Even consumers without a background in electronics are familiar with fuses. These contain a piece of wire that melts if the current passing through is too great. Once the wire has melted, the circuit is broken. There are several different types of fuses, but they all operate using the same principles.

Residual Current Devices, or RCDs, detect earth faults and then disconnect supply. Miniature Circuit Breakers, or MCBs, are electromechanical devices that protect circuits from overcurrent; unlike fuses, these devices are reusable, but they’re also more costly. Residual Current Breakers with Overcurrent (RCBO) are used in applications where there is need for protection against earth faults and overcurrents.

Metal Oxide Varistors for Circuit Protection

There is another way to protect circuits in electrical projects. It’s called a Metal Oxide Varistor or MOV. Unlike the devices described above, which offer overcurrent protection, varistors are voltage-dependent nonlinear devices that can be used to protect circuits from overvoltage. The name “varistor” is shorthand for variable resistor.

Varistors are typically made with arrays of zinc-oxide crystals; the zinc-oxide is altered with other metal oxides and the crystals are sintered into a ceramic semiconductor. The result is a crystalline microstructure that has the ability to dissipate energy in order to protect circuits.

Here are a few common questions about metal oxide varistors

Which circuit conditions does a metal oxide varistor (MOV) protect against?

Metal oxide varistors protect against high transient voltage. This may come from lightning, inductive-load switching, or electrostatic discharge (ESD). A benefit of using a metal oxide varistor for protection is that it works quickly, often in nanoseconds, limiting damage to the rest of the circuit.

Metal oxide varistor surge protection is useful in applications where there may be short surges of electrical energy.

How do you use a varistor in a circuit?

Connect varistors directly across main supplies and across semiconductor switches in order to protect thyristor bridges, MOSFETs, and transistors. It’s important to incorporate varistors into your design process early, rather than completing your design and then trying to find the best place for them.

When choosing an MOV for your project, consider the maximum working voltage and clamping voltage, the surge current, energy absorption, leakage current, maximum AC voltage, and response time.

How does a varistor protect circuits?

Metal oxide varistors work by suppressing (or clamping) the voltage to a safe level and diverting excess energy, dissipating heat to protect the circuit. Varistors are quite durable, which makes them well-suited for withstanding both high-energy surge transients as well as high-peak pulse currents.

On a technical level, what really happens is the MOV switches from a high impedance state to a significantly lower impedance state thereby allowing the surge to be diverted typically to ground (or sometimes to another phase or neutral depending on the circuit design). Once the surge event is over the MOV returns to its high impedance state thereby stopping the shunt operation.

Do varistors have polarity?

No, varistors do not have polarity. This means that they can be installed in any direction.

Learn More About Quest Components Circuit Protection Products

For starters, check out the products we offer from Maida Development Company, a world class provider of metal oxide varistors and other circuit protective devices. If you have questions about circuit protection, our expert electricians are available to help. Call (623) 333-5858 today to inquire about a product or place an order. We look forward to working with you.

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