Clamping Voltage: What is it? (vs Breakdown And Let-Through Voltage

What is Clamping Voltage?

Clamping voltage is defined as the maximum voltage allowed to pass through an electrical circuit breaker or surge protector before limiting further voltage from passing through the circuit. The clamping voltage technique is used in modern electrical equipment to protect from electrical surges.

The clamping voltage is a predefined voltage for a surge protector. The surge protector will restrict the input voltage from passing this number. Note that a surge protector is a device connected to a circuit to protect downstream equipment from spikes or surges that occur in AC circuits.

If the input voltage is more than this predefined “clamping voltage”, the surge protector will suppress the voltage to this predefined (safe) voltage.

Hence saving the device(s) from experiencing a power surge, which would damage the device and may risk the safety of those nearby. If the voltage is suppressed in this way, the voltage is said to have been “clamped”.

For example, a nominal voltage of the device is 120V and it works properly at a limit of 240V input voltage.

If the input voltage is higher than this limit, a device may be damaged. For a better operation of the device, we choose clamping voltage less than maximum sustainable voltage.

In this example, the maximum sustainable voltage is 240V. To prevent surge effect in a device, a surge protector is connected with a device that limits input voltage to slightly less than 240V. Here, we choose clamping voltage as 220V.

If a surge occurs upstream that causes the voltage to rise, the surge protector will “clamp” the voltage to a maximum of 220V.

The performance of surge protectors is tested in laboratories, and many tests are conducted on them.

Clamping Voltage vs Breakdown Voltage

Breakdown voltage is defined as a minimum voltage level at which the insulator starts behaving as a conductor and a large number of current passes through an insulator.

The electrical properties of a diode lie between insulator and conductor because diodes are made up of semiconductor materials like silicon, germanium, etc.

In reverse bias conditions, the diode behaves as an insulator. If the supplied voltage is more than reverse breakdown voltage, breakdown occurs at a junction, and currently passes through the diode.

Clamping voltage is a different concept than the breakdown voltage. A clamping voltage is a baseline beyond that the input voltage cannot go. A breakdown voltage is a baseline at which the current is zero. After crossing this baseline, the current starts flowing.

Clamping Voltage vs Let Through Voltage

The clamping voltage is also known as “Let through voltage.” In some surge protector devices, mention the clamping voltage as Let Through Voltage.

As the name suggests, it is a voltage level up to which the surge protector lets through the connected devices. And up to this voltage level, the connected devices work correctly.

What is a Good Clamping Voltage?

The value of clamping voltage for a specific device or circuit depends on how much voltage it can withstand.

A surge protector is used to controlling surges produced by the input supply. Clamping voltage decides the voltage level at which the surge protector attenuates the surge. For the best surge protector, the clamping voltage does not exceed 400V.

For a good surge protector, response time against surge is most important. Faster the response time, batter the protection. Generally, the response time of surge protection is measured in nano-sec.

A lower value of clamping voltage indicates better protection. But sometimes, it results in unnecessary tripping and a shorter life for the entire protective system.

Underwriters Laboratories (UL) suggests three levels of protection for the 120 V AC system, and it is at 330 V, 400 V, and 500 V voltage levels. The standard clamping voltage for a 120V AC system is 330 V.

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