Power Supply Systems
Q: What terms were/are given to surge protective devices for power supply systems?
A: - Lightning current arrester > type 1 / requirement class B (formerly referred to as coarse protection)
- Surge arrester > type 2 / requirement class C (formerly referred to as medium protection)
- Surge arrester > type 3 / requirement class D (formerly referred to as fine protection)
Q: Which surge protective device must I choose under consideration of the available distribution system?
A: The distribution system at the installation location of the surge protective device is decisive.
Q: What conductor cross-section is used to connect a surge protective device with and without an
integrated fuse?
A: Details can be found in the installation instructions.
Q: What maximum connecting cable lengths are required for type 1 and type 2 surge protective devices?
A: If the surge protective device has a protection level (Up) amounting to the required rated impulse
withstand voltage, the maximum length of all active conductors from the tapping point on the
voltage system to the surge protective device and from its PE connection back to the voltage
system is 0.5 m. Any functional earthing conductor (earthing symbol) required should be kept as
short as possible. It should not be run parallel to other power circuits over long distances.
If longer connection cables are required, the following must be taken into account:
Selection of an SPD with low protection level U (with an impulse current of 10kA (s/20), a voltage
drop of approx. 1000V is generated on a straight 1 metre long conductor).
A second, coordinated SPD should be installed close to the device to be protected in order to
adjust the protection level U to the rated impulse withstand voltage level of said device.
Q: Which back-up fuses are necessary for type 1 and type 2 surge protective devices?
A: Details can be found in the installation instructions.
Q: When do I need a surge protective device with integrated back-up fuse?
A: When the fuse protection of the distributor or the electric circuit of the device is higher than the
maximum fuse (stated by the manufacturer) of the surge protective device and it is not possible or
very difficult to install a back-up fuse due to lack of space.
Q: Which surge protective devices require a functional earthing conductor?
A: As a rule, all type 1 surge protective devices and, in the case of defined lightning protection zones
inside the building, also type 2 surge protection devices at the transition between zones. But also,
the first type 2 surge protective device used immediately after the meter (only in Germany see DIN
VDE 0100-443) if no type 1 surge protective device is upstream of it.
Q: Is a specific earth resistance value required for the earthing of surge protective devices?
A: No, it is not. The important thing is the equipotential bonding of all conductive systems.
Q: On which side of an RCD should an SPD be installed?
A: Seen from the conventional energy direction, upstream of the RCD. If an SPD is installed downstream
of an RCD (e.g. at the exit point of the building), the RCD must be surge-proof (S squared).
Q: In many cases, the DIN VDE 0100-443 (only in Germany) requires the installation of type 2 surge
protective devices at the supply point of a system. According to the VDN 2010 (only in Germany) one
is not allowed to install a type 2 surge protective device upstream of the meters. How should one
proceed if there are several measuring units (meters)?
A: In agreement with the power supply provider, a combined arrester (approved according to the VDN
guideline 2010) should be installed either on the busbar of the main power supply system or in a
sealable enclosure on the DIN rail.
Q: Which surge protective devices are suitable for installation in the main power supply system?
A: The VDN guideline 2010 (only in Germany) specifies the requirements to be fulfilled by type 1 surge
protective devices if they are to be installed here. As a matter of principle, all types of varistor-based
surge protective devices are prohibited for use in main power supply systems.
Q: Where can surge protective devices with a lightning current discharge capacity of 12.5 kA be
installed?
A: Basically, the peak value of the expected lightning current determines the minimum discharge
capacity of a surge protective device. If in a building with lighting protection class III, a 3- or 5-core
low voltage cable is installed in addition to the main power supply system, the lightning current is
divided between those two cables. As a result, a surge protective device with a discharge capacity of
12.5 kA usually suffices for the second low voltage cable.
Q: What are the inspection intervals for the surge protective devices?
A: The intervals for periodic maintenance tests are laid down in regulation 3 of the German Social
Accident Insurance (DGUV) (only for Germany). These are minimum requirements. The interval for
electrical installations and stationary equipment is 4 years whereas yearly inspections are
recommended for installations of DIN VDE group 700 equipment (only for Germany).
If the surge protective devices fall under the scope of the lightning protection standard DIN EN
62305, systems in lightning protection classes I + II are subject to annual inspection and those in
lightning protection classes III + IV to two-yearly inspection. However, the statutory inspection
intervals as, e.g. laid down in the building law, always have precedence.
Q: Which tests are required for surge protective devices?
A: Tests should check that the surge protective devices installed function properly in their place of
operation. Have they been installed and connected in accordance with the installation instructions
provided by the manufacturer? Do they fulfil the following requirements:
- Minimum cross-sectional area
- Size of back-up fuse
- Fully functional back-up fuses
- Surge protective devices in good mechanical condition
- Any available status indicators show functionality
- Lightning current arresters without status indicators keep an insulation resistance >500 kΩ and an IPE
< 10 μA.
Q: How high is the permissible power dissipation for surge protective devices?
A: As surge protective devices in power supply systems are always connected parallel to the electrical
equipment to be protected and do not actually cause any operating current (μA range), there is no
need to consider the power dissipation.
Information technology
Q: What kind of surge protective devices for use with information technology are available?
A: Lightning current arrester > category D1 (formerly known as coarse protection) DEHN designation TYPE1
Surge arrester > category C2 (formerly known as medium protection) DEHN designation TYPE2
Surge arrester > category C1 (formerly known as fine protection) DEHN designation TYPE3
The TYPE designation is based on the TYPE designation of the RedLine products.
Q: What information do I need to select the correct surge protective devices for information technology?
A: Above all, the kind of signal, the peak value of voltage and current, the frequency and whether the
signal is earthed or floating is of importance.
Step-by-step selection:
1.) Location of installation, lightning protection zone determined or energy to be dissipated
2.) Surge immunity of the terminal device
3.) Grounding of the system to be protected
4.) Interface requirements, transmission parameters: voltage, current, frequency
5.) Connection technology
Q: The individual surge protective devices are available in types E and D. What are these used for?
A: Type E devices are used for cases with earth related potential, also for unbalanced interfaces.
Type D devices are used for earth-potential-free, balanced interfaces.
If this does not cover a specific application, the wiring or cables beginning and ending within
equipotential structures (e.g. buildings or meshed earthing systems) should be connected to type E
devices (except video, telephone, bus systems, etc.). Should the lines or cables leave such
equipotential structures, type D devices are preferable.
Q: DC power supplies with low internal resistance can, from approx. 24V, maintain a gas discharge tube
ignited by an impulse in the low resistance state. This can occur if the cables between the power
supply and the surge protective device are short. What can I do about this?
A: Surge protective devices with integrated PTC decoupling resistors (e.g. part no. 920 314), which limit
the current to such an extent that the gas discharge tube returns to the high resistance state, can be
used here.
Q: Do surge protective devices influence the transmission path?
A: Due to their series (R and XL) and parallel (XC) resistance, they may limit given maximum conductor
lengths or stand for a bus equivalence of a bus device. In combination with the parallel resistance
(XC), the series resistance (R+XL) form a low pass. The cut-off frequency should, therefore, be
considered for the application.
Q: Which tests are required for surge protective devices?
A: Basically, the arresters should be selected according to their operating location and the interface.
If an arrester has LifeCheck, it can be tested using a DEHNrecord.
If you have DRC MCM/SCM correctly programmed, no further tests are necessary.
If you do not have the MCM/SCM, you can check the arrester using DEHNrecord M1+ or M3+.
If you have an arrester without LifeCheck, you can use the PM20 test device.
In most cases, an overloaded arrester will not let through any signal.
Q: What is the permissible power dissipation for surge protective devices?
A: In the case of surge protective devices for information technology systems with integrated ohmic
series impedance the individual power dissipation of the paths (I. x R) must be added. The R value
can be taken from the data sheet and the I value corresponds with the nominal current of the
connected equipment.
