Office Building Solution

BU I LDI NG SOLUT IONS

24

— Overvoltage protection

The protection level Uprot of the arrester must always be lower than the impulse withstand Uw of the equipment to be protected. The tolerance levels of equipment to impulse overvoltages are classified according to 4 categories (as shown in the table below), in accordance with IEC 60364-4-44, IEC 60664-1 and IEC 60730-1. For example, in a main switchboard (three-phase 400 V) the protection of category III equipment is ensured if the Uprot value is less than 4 kV. An OVR T1 arrester protects equipment due to the low protection level of OVR T1 (2.5 kV). In distribution boards, the protection of category II equipment requires the installation of a Class 2 arrester with a low protection level (1.5 kV).

For example, for a Type 2 SPD installed near terminal equipment (Category II) in a 230 V single-phase network, the protection level (called Uprot) must be chosen so that the sum of Up and inductive voltage drops on the connections is less than 2.5 kV.

O

Wh

Q

P

U

Category

U n

Exemple

P

230/400 V 400/690 V 1.000 V 1.500 V 2.500 V 4.000 V

A

I

Equipment containing particularly sensitive electronic circuits: - servers, computers, TVs, HiFi, video alarms, etc. - Household appliances with electronic programs, etc. Non-electronic household appliances, power tools Distribution boards, switchgear (circuit breakers, isolators, sockets, etc.), cable trays and their accessories (cables, busbars, junction boxes, etc.) Equipment for industrial use and equipment such as, for example, fixed motors permanently connected to fixed installations, electric meters, transformers, etc.

Installazione: Categoria IV t : y IV

Installazione: Categoria IV t : y I I

Installazione: Categoria IV t : y I

Installazione: Categoria IV t : y I

II

2.500 V 4.000 V 6.000 V 4.000 V 6.000 V 8.000 V

III

O = Origine dell’installazione; Wh = Contatore elettrico; Q= quadro elettrico principale P = Presa elettrica; U = apparecchio utilizzatore; A = apparecchiatura elettronica

O

origin of installation

P U A

socket

IV

6.000 V 8.000 V 12.000 V

Wh electrical meter Q

user equipment

main switchboard

electronic equipment

Powered by