Surge protector in switchboards > 50kA ?

I would like to share a problem I face when I have to install a surge protection device type 1 in high power electrical switchboard.

The situation is very “unconfortable” for me as a quality provider, because if a short-circuit of high value happens, though luckily probability is low, it would mean very serious safety risks …

I am the manager of a panel building company, and we receive more and more specifications requiring us to install surge protection devices type 1: they are requested for industrial sites (chemical, water station, also airport …) where they always install a lightning protection system (lightning rod, mesh cage).

The specifications I receive are not very detailed about the choice of surge protector to install, and I found out that surge protection devices available on the market cannot be connected directly to high power busbar: they cannot withstand short-circuit level higher than 50kA, but I regularly have specifications for switchboards of 70kA or more.

The photo below is an example of surge protection device (in the circle) connected to high short-circuit level busbars.

How to solve this problem?

Is there a way to reduce the short-circuit level to be compatible with the limitations of the surge protection device?

Or wouldn’t it be better to have surge protection devices with higher short-circuit level available on the market?

Thanks for your opinion



  • Firstly, if the prospective short circuit available is at or above 50 kA the board is close to the supply transformer. The transformer should be equipped with Arcing horns on the HV side to dissipate to ground most of the energy of a lightning event on the HV circuits.
    On the LV take off from the transformer after the main air circuit breaker you should connect a surge supressor 3 phases + neutral to earth. The surge supressor should be provided with fuse isolation. The fuse limits the current in the case of a fault in the surge supressor unit & it allows isolation for replacement. Even with a board whose prospective short circuit current is 70 kA it is generally not necessary to fuse the suge supressor at > 250 Amps or to provide > 35 sq mm cable from the bus bars to the fuse & from the fuse to the surge supressor. This cable (for type I surge supressor) will not conduct any current in normal operation & will be cold when required to conduct the pulse of current during a surge event. It will survive the short surge pulse without
    Note that if you provide surge supression for type I only the surge supressors will not conduct during a minor transient overvoltage. Several thousands of volts can be experienced at the busbars & the surge supressors will not assist in relieveng this overvoltage. Large & robust motors or distribution cables will tolerate this type of transient but electronic items will not. Type II or Type II/III surge supression should always be provided for electrical networks in factories where instrumentation, PLCs, computers etc are required.

  • Surge protection is available in my part of the world at 100 kA and 150 kA ratings if your design requires this level of protection.

  • Dear Mr. Bobby,
    There are a lot of posts and articles in this portal where you will get information about surge devices. Also please search wikipedia regarding surge devices. As per my experience, the selection of surge devices is not only Dependant on the current, the short-circuit withstand , but also on the following factors(which i may be correct or incorrect, please suggest)
    1) Switching overvoltages: For eg: if a capacitor is frequently switched on and off, there is brief period where over-voltages are introduced in the system. if the load is a electronic device for eg : medical equipment, this momentary overvoltage is sufficient to damage the equipment.
    2) Transient surges in the system due to harmonics
    The TVSS( Transient Voltage surge suppressor) is primarily for one time use since the cost of surge suppressor is small compared to the cost of equipment.
    Please contact obo-betterman/ ASCO/Schneider/ABB or check these company websites for more information.
    Thanks and Regards

  • Many thanks for your advices but I would like to add more details about two issues :
    My first problem is the technology of the surge protection devices and the link with the standard installation
    Hereafter the extract from the standard IEC 60364-5-534 :
    534.2.3.5 Selection with respect to the expected short-circuit current
    The short-circuit withstand of the SPDs (in case of SPD failure) together with the specified
    associated (internal or external) overcurrent protective device shall be equal to or higher than
    the maximum short-circuit current expected at the point of installation taking into account the
    maximum overcurrent protective devices specified by the SPD manufacturer.
    In addition, when a follow current interrupting rating is declared by the manufacturer, it shall
    be equal to or higher than the expected short-circuit current at the point of installation. (Ifi> Isc)

    However, when I look at the different offers on the Type 1 market, the technology most frequently used is the spark gap with follow current. This follow current interrupting rating (Ifi) is 50kA for most manufacturer of Surge arrester . No more
    So if we take into account the standard IEC 60364, it is not possible to install Type 1 surge arrester with spark gap technology on high power busbar with Isc > 50kA . With this kind of technology we are limited at 50kA(50hz) max

    The second problem concerns the DIN Rail surge arrester whose the short circuit withstand does not exceed a maximum of 50kA if I have a right understanding of the characteristics given by manufacturers.
    In these circumstances I do not see how to install surge arresters on the high power busbar with > 50kA

    May be this explanation is clearer than previous one.
    Tks for your comments

  • Hi,

    I am looking for 25 cabinets with specification below:


    The LV electrical distribution panel must be provided with equipment protection, monitoring, reporting and consistent with the pattern mentioned below.

    The distribution panel must be designed with tin coating against corrosion. It must be modular for easy moving, removable and can be combined with other cabinets on the sides for future extensions. It will be designed to receive ample apparatus defined below.

    The cabinet must be ventilated to fight against condensation. All cables and son of control, signaling, arrival and departure will be connected to the bottom on terminals or lugs calibrated after each departure and perfectly located. All parts of the cabinet will be connected and linked with braids mass to ensure electrical protection.

    The wiring will be made in flexible cable easily accessible from the ends inside the plastic chutes.

    The lower part should be easily accessible to the front to allow movement of cables.

    Circuit breakers are compact type with adjustable sensitivity of fault current. The orders of the circuit breakers will be reduced to the front of the cabinet.

    All instrumentation and control (Lights, Ammeter, Voltmeter, Frequency) will be reduced so as to facilitate maximum all work troubleshooting.

    Protective equipment:
    – A (01) General Breaker Tetra Polar 400A.
    – A (01) Tetra Polar Breaker 125A.
    – A (01) Tetra Polar Breaker 100A.
    – Three (03) Tetra Polar 80A breakers.
    – Three (03) Tetra Polar 40A breakers.
    c-control equipment and signaling:
    – Ammeter + switch.
    – Voltmeter + commutator.
    – Frequency.
    – Set of warning lights under voltage.
    – All circuit breaker reset 2A.
    – Set of busbars.
    – Lots of wiring accessories.

    The cable that connects the general cabinet power distribution low voltage (LV) and the table of power distribution section of the transmitter will :

    • 4×35 mm ² for absorbing wave power 50 KVA (3P + N).

    The length of each cable is 100m.

    The cable grounding should also be provided and must be isolated. It will be inside the main cable or separated.

    Can someone help me to find any supplier because I can not find any who can do a complete solution above.


    • Hi Matej.

      Which country is this switchboard for?

      What is its application.

      I sense it is not for UK use.

  • Boby, we are investigation engineers that specialise in power quality and surge protection.

    Short circuit current is not the same as surge current nor lightning current. All are different and not to be used equally. This has been expanded in prior blogs. Basically lightning current flows via earthing and only some energy gets through to conductors (NOT all the strike energy). Power poles and transformers already have MOV’s to prevent transformers and cable insulation from failure. Rarely will a surge of 20kA reach your MSB surge arrestor, which is why IEC61643-1 only tests to 20kA. MOVs of higher kA only give longevity, as the kA rating is for a SINGLE hit. Higher kA means more hits at lower kA. This does not assure the let through voltage though, so MOVs on board are just to prevent dielectric (cable and winding insulation) breakdown.

    The fuse protecting the MOV should be rated to clear at the MSB fault level, that is the key.
    Having a MOV within the same chamber is risky in case the MOV fails and escalates into the chamber.
    If you are actually trying to protect equipment then the MOV is only 2% of the energy capture solution.
    To protect for the other 98% of energy, typical of mains surges from grid and building, use SASD at DB’s.

    Typically MSB should have I2RLSA230-150/20 (with a 63A fuse/breaker rated according to fault level).
    Typically DB should have I2R240W10K (with 20A breaker) for best equipment protection. The overload protection provides a limit of the let through energy and its steady rating is not the key but its i2t rating. As you can see we use the Transtector MOV and SASD products to suit the application, rather than one device does all. Both MOV (150kA) and SASD (10kA) are DIN mount units. Interesting to note that a 10kA SASD has more energy (long pulse rated) capability (not kA) capability than a MOV (short pulse rated).

    The energy protection sequence is thus 1. Earthing, 2. MOV at point of entry only, 3. SASD at DBs.
    Coordinated voltage clamping is the priority, matching what it needs to protect.

    Hope this helps.

  • […] protection device type 1 in high power electrical switchboard. I already asked this question on another blog, and I’m trying to get more feedbacks from electrical […]

  • The photo below is an example of surge protection device (in the circle) connected to high short-circuit level busbars

  • It is very simple:

    The SPD has a max prefuse size to protect the SPD against overload by too high short circuit currents, caused by spark gap SPDs.
    In this case you have to use an arrester pre-fuse (back-up fuse) , the max. size you will find in the SPD manufacturers catalogue.

    An lightning protective SPD must resist acc. to standard IEC 62305 max. Iimp = 25kA per pole if used in LPL 1 (totally all poles 100kA 10/350µs impulse )
    Additional stress would be a too high the short circuit current. To extinguish a short cicuit flow….you need a obvercurrent protection, which is a fuse.
    A SPD is not a overcurrent protection
    For any lightning protection questions contact: (

  • Hello Friends this is not comments on your topics but i m also facing the problems with TVSS surge protecting device. I had been using surge protecting device in numbers of panels. before the Surge protector Protect the circuit with fused or burning out the device. the Lead from Lightening tip to Surge protector device melted down. whats may be thew cause?
    this is happens country like Nepal in hilly mountaineering areas.

    Upendra badal

  • Hello friends surge protector can be install at incoming supply or at out going supply. plz tell me we mainly use it on outing supply i think that it is not a right way to install .

  • Thank you for another wonderful article. The place else
    may anyone get that kind of information in such a perfect way of writing?

    I’ve a presentation next week, and I’m on the
    search for such information.

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