COMBI521
EN - 52
6.7.1. Test types
The protection of electrical lines is the essential part of a project to guarantee correct
functionality and avoid injury to persons or damage of property. To this purpose, the safety
guidelines impose on electrical designers to also design the electrical installation in order to
obtain:
1. The protection from short-circuits, i.e. the breaking capacity of the protection device
must not be lower than the prospective short-circuit current in the point in which the
device is installed.
2. The protection from indirect contacts.
In order to verify the a.m. conditions, the instrument performs the following functions:
Ra
(Ut) Check of protection from indirect contact
– According to the type of
distribution system (TT, TN, IT) set by the user, the instrument performs the
measurement and verifies the condition imposed by the guidelines. Should it
be reached, the instrument gives a positive outcome (see § 12.6, 12.8, 12.9).
Br.Cap Check of protection’s breaking capacity
– The instrument detects the value
of the line impedance upstream of the measured point, calculates the
maximum value of short-circuit current and gives a positive outcome if the
value is lower than the limit set by the user (see § 12.5).
TripT
Check of the coordination of protections
– The instrument detects the value
of the line impedance upstream of the measured point, calculates the minimum
value of short-circuit current and the corresponding value of the trip-out time (t)
of the protection device, and gives a positive outcome if the value is lower than
the limit set by the user (see § 12.10).
STD
Generic test
The following table summarizes the possible measures executable depending on the type
of system (TT, TN and IT), of selected modes and the relationships that define limit values.
