Guide to AC SPD – Selection and Application

Guide to AC Surge Protector

- Selection and Application Principles

Created by: Glen Zhu | Updated Date: Nov 2, 2022

To begin with, we must understand the surge protector’s regulations.

AC Surge Protection Device SPD Selection and Application

Regulation 443.4 of BS 7671:2018 states:

Protection against transient overvoltages shall be provided where the consequence caused by overvoltage could:

  1. Result in serious injury to, or loss of human life
  2. Result in interruption of public services and/or damage to cultural heritage
  3. Result in interruption of commercial or industrial activity
  4. Affect a large number of co-located individuals

For all other cases, SPDs shall be fitted to protect against transient overvoltages, unless the owner of the installation declines such protection and wishes to accept the risk of damage to both wiring and equipment as tolerable.

Note: Always refer to the latest updated Standards. 

What is AC Surge Protection Device(SPD)?

Equipment connected to Alternating Current (AC) networks can be easily subjected to a multitude of undesirable electrical phenomena. AC surge protection device is designed to protect electrical systems and equipment from surge events by limiting transient voltages and diverting surge currents.

Transient voltage and power surges can present a great risk to both individuals and equipment, which is why the role surge protection plays should not be overlooked when it comes to safety.

Earthing Systems of AC Surge Protection(TN-C、TN-S、TN-C-S、TT、IT)

According to the IEC’s various protection methods and terms, low-voltage power supply systems are classified into three types: TT, TN, and IT systems, with TN systems further classified into TN-C, TN-S, and TN-CS systems.

As a result, the SPD should be chosen in accordance with the various grounding methods of the low-voltage power supply system.

TN-C System

TN-S System

TN-C-S System

TT System

IT System

For instance, when the TN AC power supply system is used for power supply, the power distribution line drawn from the building’s main distribution box must use the TN-S grounding method.

Selection of AC Surge Protector

AC SPD Types

There are three different types of surge protection devices (SPDs) according to IEC 61643-11:2011 and EN 61643-11:2012+A11:2018.

  1. Type 1 / Class I / Class B
  2. Type 2 / Class II / Class C
  3. Type 3 / Class III / Class D
AC Surge Protection Device series

For the AC power supply system, choosing the right SPD ensures that the equipment has the longest possible lifespan. Keep these essential considerations in mind when choosing SPDs for your AC power supply system:

  • Make sure if the supply is Single Phase or Three Phase.
  • Determine the SPD’s voltage protection level UP. To protect electrical equipment from overvoltage, the protected electrical equipment’s impulse withstands voltage should be greater than the surge protector’s voltage protection level UP.
  • Get the right number of ports or outlets.
  • Check to see whether it is a transient voltage surge protector and if it has a TUV mark.
  • The system won’t be harmed if the SPD is chosen too large, but it will fail sooner if it is chosen too tiny.
  • Certified SPDs include a failure indication (often in the form of an indicator light or flag) to allow maintenance personnel to easily determine whether the SPD is still functional. A regular inspection is essential. SPDs with a nonfunctional indicator should be replaced as soon as possible.

Application of AC Surge Protector

AC Surge Protection for E-Mobility

As electric vehicles (EVs) become more widely available in many countries, the availability and safety of electric vehicles and charging stations has been identified as a critical factor.

Considering that the vast majority of vehicle electronics at charging stations are now wired into the grid, Once transient voltages are coupled into the vehicle through this galvanic connection, they become a serious threat.

LSP ranges of AC surge protectors for E-Mobility in the power supply and inspection circuit could be used to safeguard the charging station’s electronic components. 

Type 1+2 AC Surge Protection Device SPD

· LSP DIN-rail AC SPD for single and three phase - FLP12,5 series

This type of surge protection device SPD can protect all electrical installations against lightning strikes by discharging the current created from a lightning surge and keeping it from spreading to the equipment, which characterized by a 10/350 µs and 8/20 µs lightning current waveform.

Type 1+2 AC SPD FLP12,5-275/4+0

for 3 phase TN-S networks

Type 1+2 AC SPD FLP12,5-275/3+1

for  3 phase TT and TN-S

Type 1+2 AC SPD FLP12,5-275/3+0

for  3 phase TN-C networks

For installation, it should be installed at the origin of the AC installation equipped with LPS.

Wiring Diagram:

· LSP DIN-rail AC SPD for single and three phase - FLP7 series

LSP SPD FLP7 series use Metal Oxide Varistor (MOV) and/or Gas Discharge Tube (GDT) circuits to protect electrical devices from spikes in alternating current power.

Type 1+2 AC SPD FLP7-275/4+0

for 3 phase TN-S networks

Type 1+2 AC SPD FLP7-275/3+1

for 3 phase TT and TN-S

Type 1+2 AC SPD FLP7-275/3+0

for 3 phase TN-C networks

These series are designed to be connected in multi-pole configurations to protect single-phase, 3-phase, and 3-phase+Neutral AC networks, and for TN-C, TN-S, TN-C-S TT, and IT power supply systems.

Wiring Diagram:

Type 2 AC Surge Protection Device SPD

· DIN-rail AC SPD for single and three phase - SLP40 series

LSP SPD SLP40 series are intended as a protection against transient overvoltage caused by fast switching operations or indirect hits of lightning strokes (residuum effects), Which characterized by an 8/20 µs lightning current waveform.

AC Type 2 surge protection device SPD

SLP40-275/4+0 for 3 phase TN-S networks

AC Type 2 surge protective device SPD

SLP40-275/3+1 for 3 phase TT and TN-S

AC Type 2 surge protector device SPD

SLP40-275/3+0 for 3 phase TN-C networks

AC Type 2 surge protection device SPD

SLP40-275/2+0 for single phase TN-S

AC Type 2 surge protective device SPD

SLP40-275/1+1 for single phase TT and TN-S

AC Type 2 surge protector device SPD

SLP40-275/1+0 for single phase TN-S, TN-C, TT (only L-N)

These series are rated for indoor use(sub-distribution or machine control cabinets) or fixed into a waterproof box for outdoor use.

Wiring Diagram:

AC Surge Protector for Industrial Sites

The equipment used in your manufacturing facilities is very sensitive and vulnerable to lightning and switching surges. A professional approach to lightning and surge protection will guarantee your industrial sites a long life.

Type 1 AC Surge Protection Device SPD

· LSP DIN-rail AC SPD for single and three phase - FLP25 series

LSP FLP25 series is designed to protect industrial service entrances at an industrial site.

Type 1 AC SPD FLP25-275/4+0

for 3 phase TN-S networks

Type 1 AC SPD FLP25-275/3+1

for 3 phase TT and TN-S

Type 1 AC SPD FLP25-275/3+0

for 3 phase TN-C networks

LSP components greatly increase the service life and trouble-free operation of the related equipment by shielding the technology in the power supply network from lightning currents and overvoltages. Pick from a wide range of surge protection products made by us.

Wiring Diagram:

Why Buy from LSP?

We know you have a lot of options. On the surface, they may all appear the same. What you can’t see is what makes the difference.

LSP provides solid engineering, proven reliability, and exceptional customer service. Before they are sold, all of our products are subjected to stringent quality control, with independent testing agencies confirming that they meet or exceed the most recent safety and performance standards. We can back our products with industry-leading warranties and responsive customer service. Here’s what makes LSP unique.

Contact us freely to get more AC SPD informations.

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