Overvoltage arresters installation guide
The choice of the overvoltage arresters will be made according to :
- Type of overvoltage arresters : According to the NFC 15-100 standard, the installation of Type 1 overvoltage arresters is compulsory for every structure equipped with a lightning rod.
- the nominal discharge current : In
(20 times - 8/20 µs wave form)
- the maximum discharge current : Imax
(1 time - 8/20 µs wave form)
- the protection level : Up
(residual voltage at In)
The overvoltage arresters are connected in parallel on the equipment to be protected, between the active conductors and the earth. They must be fitted with interrupt devices guaranteeing absolute safety even when the unit is due for replacement.
INDELEC overvoltage arresters are available by unit (one unit per phase) to be clipped onto a symmetrical 35mm rail or in pre-wired cabinet including overvoltage arresters and circuit breakers.
Connection cables between arresters and the lines to be protected must be identical in section to the lines (50mm2 max.) . The earthing cable section must equal half that of the main protection conductor of the installation with a minimum of 4mm2 copper and a maximum of 35mm2 copper. If a lightning rod is installed on the structure, the minimum section of the earthing cable is 10mm2 copper.
Overvoltage arresters installation scheme
The stepped protection principle
When lightning strikes electrical equipment, the effect can be compared to an extremely violent shock wave capable of destroying a considerable amount of equipment. The energy held within this destructive wave may be such that several layers of overvoltage arresters are required to bring it down to an acceptable level.
A high energy DGS overvoltage arrester positioned at the front of the installation breaks the lightning shock wave thereby dissipating a lot of the energy. The residual voltage which gets through to the electrical equipment is limited thanks to a second protection stage using DGT type overvoltage arresters and, if necessary, a third stage using DGX arresters.
The cable length between the protection levels will be longer than 5 metres in order to achieve the stepped protection. On the contrary, an inductance must be installed between the overvoltage arresters.
Stepped protection scheme