What is Surge Protective Device?

Surge Protective Devices (SPDs), also known as surge protectors or lightning arrestors, are devices designed to protect electrical and electronic equipment from voltage spikes or surges, which can be caused by lightning strikes, electrical faults, or other factors. There are three main types of SPDs: Type 1, Type 2, and Type 3, each designed for specific applications and installation points within an electrical system. Here are the key differences between these types:

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What is the principle of the surge protector?

SPD is designed to limit transient overvoltages of atmospheric origin and divert current waves to earth, so as to limit the amplitude of this overvoltage to a value that is not hazardous for the electrical installation and electric switchgear and controlgear.

SPD eliminates overvoltages

in common mode, between phase and neutral or earth;
in differential mode, between phase and neutral.
In the event of an overvoltage exceeding the operating threshold, the SPD

conducts the energy to earth, in common mode;
distributes the energy to the other live conductors, in differential mode.

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Common characteristics
Uc: Maximum continuous operating voltage
This is the A.C. or D.C. voltage above which the SPD becomes active. This value is chosen according to the rated voltage and the system earthing arrangement.
Up: Voltage protection level (at In)
This is the maximum voltage across the terminals of the SPD when it is active. This voltage is reached when the current flowing in the SPD is equal to In. The voltage protection level chosen must be below the overvoltage withstand capability of the loads. In the event of lightning strokes, the voltage across the terminals of the SPD generally remains less than Up.
In: Nominal discharge current
This is the peak value of a current of 8/20 µs waveform that the SPD is capable of discharging minimum 19 times

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Why is In important?
In corresponds to a nominal discharge current that a SPD can withstand at least 19 times: a higher value of In means a longer life for the SPD, so it is strongly recommended to chose higher values than the minimum imposed value of 5 kA.

Difference between Type1, Type2,Type3 Surge Protective Devices SPDs?
Type 1 SPDs:
Also known as “Type 1 Primary Surge Arrestors” or “Service Entrance Surge Arrestors.”
Installed at the service entrance or main distribution panel to protect against direct lightning strikes and severe surges originating from external sources.
These SPDs are designed to handle high-energy surges and are typically rated with a higher surge current capacity.
They are commonly used in industrial, commercial, and residential applications.
Type 1 SPD is characterized by a 10/350 µs current wave.

Type 2 SPDs:
Also known as “Type 2 Surge Protective Devices” or “Main Distribution Panel Surge Protectors.”
Installed downstream from the Type 1 SPD at the distribution panel or subpanel to protect against the secondary effects of surges and transient voltage spikes.
Designed to protect against smaller surges that may enter the electrical system through branch circuits.
These SPDs are commonly used in residential and commercial buildings.

Type 2 SPD is characterized by an 8/20 µs current wave.

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Type 3 SPDs:

Also known as “Type 3 Point-of-Use Surge Protectors.”
Installed at the point of use, near sensitive electronic devices, and connected to individual outlets or devices.
Provide localized protection for specific equipment and are commonly found in power strips, surge protector strips, or as built-in protection in electronic devices like computers and televisions.

Designed to protect against low-level surges and transient voltages.

Type 3 SPD is characterized by a combination of voltage waves (1.2/50 μs) and current waves (8/20 μs).

Type 1+2 surge protection

Type 1 surge protection (lightning current arrester) constitutes the first stage in the protection concept. It can discharge very high energies, e.g., caused by a lightning strike, to ground. Type 1 surge protective devices (SPDs) are usually installed in the feed-in or main distribution system. For additional energies with lower surge voltage pulses, type 1+2 combined lightning current and surge arresters are required.

In summary, the key difference between Type 1, Type 2, and Type 3 SPDs is their installation location and the level of protection they offer. Type 1 SPDs are at the service entrance and protect against severe external surges, Type 2 SPDs are at distribution panels and protect against secondary surges, while Type 3 SPDs are at the point of use and protect specific devices from low-level surges. In many cases, a comprehensive surge protection strategy may involve the use of multiple types of SPDs at different points in an electrical system to provide layered protection against surges.