Overview
Failures are very often the result of overvoltages caused by:
• Atmospheric discharge or
• Electrostatic discharge.
First of all, we want to introduce you to the lightning protection zone concept, on which the protection against overvoltage is based.
At the end of this section, you will find rules for the transitions between the individual lightning protection zones.
Note
This section can only provide information on the protection of aprogrammable logic controlleragainst overvoltages.
However, a complete protection against overvoltage is guaranteed only if the whole surrounding building is designed to provide protection against overvoltages.
This refers especially to constructional measures for the building already in the planning phase.
If you wish to obtain detailed information on overvoltage protection, we therefore recommend you to address your Siemens contact or a company specialized in lightning protection.
Assembling and Installing Systems
A.9.1 Lightning Protection Zone Concept
Principle of the Lightning Protection Zone Concept According to IEC 61312-1/DIN VDE 0185 T103
The principle of the lightning protection zone concept states that the volume to be protected, for example, a manufacturing hall, is subdivided into lightning protection zones in accordance with EMC guidelines (see Figure A-6).
The individual lightning protection zones are constituted by the following measures:
The external lightning protection of the building (field side) Lightning protection zone 0
The shielding of buildings Lightning protection
zone 1
The shielding of rooms Lightning protection
zone 2
The shielding of devices Lightning protection
zone 3
Effects of a Lightning Strike
Direct lightning strikes occur in lightning protection zone 0. The lightning strike creates high-energy electromagnetic fields which can be reduced or removed from one lightning protection zone to the next by suitable lightning protection
elements/measures.
Surges
In lightning protection zones 1 and higher, surges can result from switching operations and interference.
Diagram of the Lightning Protection Zones
The following diagram illustrates a lightning protection zone concept for a detached building.
Lightning Protection Zone 0, Field Side
Lightning Protection
Lightning Protection
Zone 3 Device Energy-
Technical Cable
Lightning Protection Zone 1
Building External
Lightning
Shield (Steel
Reinforcement) Room Shield (Steel
Reinforcement) Device Shield (Metal Housing)
Metal Component
Non-Electrical Cable
Information-Technical Cable Lightning Protection Equipotential Bonding Local
Equipotential Bonding Internal
Cable
(Metal)
Galvanic Connection Protection
Zone 2
Figure A-6 Lightning Protection Zones of a Building
Principle of Transitions between the Lightning Protection Zones
At the transition points between the lightning protection zones, you must take measures to prevent surges being conducted further.
The lightning protection zone concept also states that all lines at the transitions between the lightning protection zones that can carry lightning stroke current must be included in the lightning protection equipotential bonding.
Lines that can carry lightning stroke current include:
• Metal pipelines (for example, water, gas and heat)
Assembling and Installing Systems
A.9.2 Rules for the Transition between Lightning Protection Zones 0 and 1
Rule for the Transition 0 <-> 1 (Lightning Protection Equipotential Bonding) The following measures are suitable for lightning protection equipotential bonding at the transition between lightning protection zone 0 <-> 1:
• Use grounded, spiralled, current-conducting metal strips or metal braiding, for example, NYCY or A2Y(K)Y, as a cable shield at the start and end
• Lay the cables in one of the following ways:
-- in continuous metal pipes that are grounded at the start and end -- in ducts of armored concrete with continuous armoring
-- on closed metal cable racks grounded at the start and end
• Use fiber-optic cables instead of lightning stroke current-carrying cables.
Additional Measures
If you cannot take the measures listed above, you must install a high-voltage protector at transition 0 <->1 with a relevant lightning conductor. Table A-3 contains the components you can use for high-voltage protection of your plant.
Table A-3 High-Voltage Protection of Cables with the Help of Surge Protection Equipment Ser.
No.
Cables for ... ... equip transition point 0 <--> 1 with:
Order No.
1 3-phase TN-C system 1 piece of DEHNbloc/3 lightning conductor
phase L1/L2/L3 to PEN
900 110*
5SD7 031 3-phase TN-S system 1 piece of DEHNbloc/3 lightning
conductor
phase L1/L2/L3 to PE
900 110*
5SD7 031 1 piece of DEHNbloc/1 lightning
conductor N to PE
900 111*
5SD7 032 3-phase TT system 1 piece of DEHNbloc/3 lightning 900 110*
Table A-3 High-Voltage Protection of Cables with the Help of Surge Protection Equipment, continued Ser.
No. ... equip transition point 0 <--> 1 Order No.
with:
Cables for ...
AC TT system 1 piece of DEHNbloc/1 lightning
conductor phase to N
900 111*
5SD7 032 1 piece of DEHNgap B/n N-PE light-
ning conductor N to PE
900 130*
2 24 VDC Power Supply 1 piece of Blitzductor VT lightning conductor,
type A D 24 V --
918 402*
3 MPI bus cable, RS 485, RS 232
(V.24) 1 piece of Blitzductor CT lightning
conductor, type B 919 506* and 919 510*
4 Inputs/outputs of digital modules
24 V DEHNrail 24 FML 901 104*
5 24 VDC power supply module 1 piece of Blitzductor VT lightning conductor,
type AD 24 V --
918 402*
900 111*
5SD7 032 6 Inputs/outputs of digital modules and
120/230 VAC power supply 2 pieces of DEHNbloc/1 lightning
conductor 900 111*
5SD7 032 7 Inputs/outputs of analog modules up
to 12 V +/--
1 piece of Blitzductor CT lightning conductor,
type B
919 506* and 919 510*
* You can order these components directly at: DEHN + SệHNE GmbH + Co. KG Elektrotechnische Fabrik Hans-Dehn-Str. 1 D-92318 Neumarkt
Assembling and Installing Systems