baltur TBG 450LX MC, Instruction Manual For Installation, Use And Maintenance

Page: 68 / 96

Only by way of example, find below the calculation of the maximum
fault loop impedance allowed in a "TN" system, with the definition of
the protection fuse size, brand and model.
Use the documentation showing the intervention curves related to the
brand and the model of the fuse used for the protection, having the size
indicated in Table 2.
Intercept the curve related to the selected fuse size with regard to the
intervention time "Ti".
EXAMPLE NO. 1:
CALCULATION OF THE MAXIMUM FAULT LOOP IMPEDANCE
System TN
Maximum intervention time Ti = 5 s
Fuse size In = 50 A
Curva_T
agliafusibili
→ Ia ≈ 160 A
Enter the value of "Ia" obtained from the diagram in the formula provi -
ded in A.1.2 of EN60204:2016 to obtain the maximum value of "Zsn"
(fault loop impedance):
Z
s
(n)
≤
2
3 x
U
0
I
a
Z
s
(n)
≤ 0.958 Ω
Uo = 230 V (Nominal voltage with respect to PE)
Ia = 160 A (Intervention current with time Ti)
Ensure a dimensioning safety margin of 10%.
Z
s
=
Z
s
≤ 0.860 Ω
Z
s
(n) x 0,9
CAUTION / WARNINGS
This condition must always be verified by the installer after con -
necting the burner to the system.
The fault loop impedance value must be measured with instruments
complying with the standards IEC 61557-3 following the procedure in-
dicated in A.1.4.2 of EN 60204-1.
ENGLISH
20 / 46
0006160271_202007