Technical information

2/25
1SDC210033D0202
Circuit-breakers for oversized neutral protection
Main characteristics
The SACE Tmax XT range of circuit-breakers with oversized neutral is used in certain applications
where harmonics or unbalance loads or single phase create an overload on the neutral conductor.
Under these conditions, a current of a considerable value could travel along the neutral conductor.
In particular, third-order harmonics and relative multiples add together on the neutral and give rise to
a current value that could be higher than the one which travels along the phase conductors.
For this reason, circuit-breakers with oversized neutral provide adequate protection in installations
where the neutral conductor is sized with a larger section than the phase conductors.
The main types of equipment that generate harmonics are given below by way of example:
Q personal computers;
Q fluorescent lamps;
Q static converters;
Q no-break power units;
Q variable speed drives;
Q welding machines.
By and large, the wave shape is distorted owing to the presence of semiconductor devices able to
conduct for a fraction of the entire cycle, creating discontinuous trends and consequently introduc-
ing numerous harmonics.
Consult the “Electrical installation handbook” ABB SACE guide vol. 2 for further details.
Characteristics of circuit-breakers for oversized neutral protection
XT2 XT4
Size
(G2.1)
[A] 160 160/250
Uninterrupted nominal current, In [A] 10, 63, 100 40, 63, 100, 160
Poles [Nr.] 4 4
Rated service voltage, Ue
(G2.4)
(AC) 50-60Hz [V] 690 690
Rated insulation voltage, Ui
(G2.5)
[V] 1000 1000
Rated impulse withstand voltage, Uimp
(G2.6)
[kV] 8 8
Versions Fixed, Withdrawable, Plug-in Fixed, Withdrawable, Plug-in
Breaking capacity N S H L V N S H L V
Trip units
Electronic Electronic
Ekip N-LS/I
VV
Interchangeability
QQ
Q
Complete circuit-breaker
V Loose trip unit