Power Distribution and Management

How to choose the right surge protector?


How to choose the right surge arresters ?

Choosing the right surge arrester and protective circuit breakers involves a considering a wide range of parameters related to types of surge protection devices, circuit breaker arrangements and risk assessment.

Three rules of thumb for choosing surge arresters

Now that we’ve established that surge arresters should be at the heart of a lightning protection system, it’s time to think about how to choose the right surge arrester. Easier said than done. Here are some rules of thumb for installing a surge protection device (SPD):

  1. Familiarise yourself with types, or category, of SPDs.
  2. Assess the risk of lightning strikes and discharge capacities.
  3. Use devices to protect the surge arrester itself.

3 types of surge protection devices

To protect a distribution switchboard, you need only install a Type 2 arrester with discharge capacity In>5kA.(8/20).

Risk assessment

Assessing risk is generally a complex, painstaking process. A good starting point is to think about what kinds of areas are most and least at risk. You can then consider the type of SPD best suited to the kind of building you’re planning to protect – if it has a single service entry switchboard.

Lightning strikes 90% of the earth. Some parts are highly prone to lightning strikes. Some hardly at all. For example, lightning density (number of strikes per kilometer per year) in Belgium is 1ng, while in South Africa it is 150ng.

Lightning strikes densities, world map

However, lightning density is not per se a risk. France, for example, includes Ng it in its national standard NF C 15-100. Spain does not.

One or two tips for risk assessment

Use European to risk assessment standard EN 62305-2. Some countries make it compulsory to use the standard when considering surge protection for big and or highly sensitive buildings like industrial facilities, hospitals, and data centers.

Otherwise, bear this rule of thumb in mind: always install a Type 2 surge arrestor. If the distance between the surge arrestor and the equipment to be protected is greater than 10 metres, then add a Type 2 or Type 3 arrester.

Protect your surge protection devices

Although surge arresters don’t trip, the following end-of-life scenarios are possible:

  1. Thermal runaway caused by the constant excessive constraints of an SPD not exceeding its lightning attributes could lead to the slow destruction of internal components. The disconnection of the SPD is provided by a thermal fuse associated with the electronic components (MOVs) inside the SPD.
  2. A short-circuit due to exceeding the maximum flow capacity or due to a fault under 50hz from the electrical distribution network (e.g. neutral rupture, phase-neutral inversion). The disconnection of the SPD is provided by an  external or integrated short circuit protection device like fuse or circuit breaker. Although you may have to choose an external circuit breaker, more and more manufacturers incorporate them in the same enclosure.

You choose a circuit breaker according to the short circuit current in the building where the surge arrester is installed. So, for example, a disconnection circuit breaker with a short-circuit breaking current of <6kA is suitable for a residential building. For an office, it is usually 15kA or 20kA.

But determining matches is a delicate business. Manufacturers publish surge-arrester/circuit-breaker coordination tables .

Choosing the right surge arrester and protective circuit breaker – at a glance

The schematic below gives you an idea of the basic parameters you should factor into your choice of surge protection.

How to Choose a Surge Protector

Better still – make an informed, comprehensive choice of surge arresters

Check out and download this software (5.2Mo) to know about choosing the right surge protection devices and circuit breakers for the right application.

12 Responses
  1. victor

    hello didier,
    can you explain a bit more why it’s better to protect your SPD with circuit breaker instead of fuse ?
    thanks for your clarification

  2. mark rehert

    The email invite for the survey said that I would be entered into a raffle but I was never asked for my contact information.

    • Jennifer Wendt

      Hi Mark,
      We apologize for this issue. Your name is submitted into the list of potential winners and we appreciate your patience and response to this matter. Good luck!

  3. Pat

    Thanks for the timely advice as we approach the summer season.

  4. Marilyn Savela

    Thank you for the survey and helping us understand…..We do have power surges, and the power shuts off for ten minutes, sometimes only on and off
    or longer….then reset everything.

  5. Abdul Whab

    what is the difference between class 1 and class 2 surge arrestor?


    Is Class-II SPD is suitable for Home System. If yes, which SPD we use like model, power etc. we have 220v 3 phase system in our region.

  7. David Li

    Hi Didier,
    In a building, we have main LVSB, floor main DB, and terminal DB’s, is it required to install SPD in all switchboards, distribution boards, IT power distribution boards?

  8. Engr Kamran

    i use NW800A TP ACB (Masterpack ) Schneider make for my main L.T panel . please suggest me Is NW800A ACB required for separate SPD for our system safety protection?