Brochure

ESG
8.598.59
8.598.59
8.59
Functional Three-phase switch for Three-wire system
(Fig. 16) (Fig. 16)
(Fig. 16) (Fig. 16)
(Fig. 16)
Two SSRs may be used to control a Y or a delta load in a three-wire system. A third SSR would be required in phase
C if the centre of the Y load were grounded, as in a four-wire system. SSR voltage rating must be greater than line to
line voltage for three-wire systems and line to ground voltage for four-wire systems (with neutral ground).
SSRs are most commonly used in three-phase applications to control motors, where their current ratings depend as
much on locked motor current as they do on normal run current and proper heat sinking. Where a motor rating is not
given, a minimum SSR current value can be estimated from the device surge curves, using the general rule of six
times the motor run current for one second. This value must also be commensurated with thermal and lifetime
requirements.
Phase A
Mechanical
savety disconnect
AC
SSR
Series or
parallel control
Phase B
AC
SSR
Phase C
Delta
load
Wye load
(ungroundet)
Fig. 16: Functional three-phase switch for three-wire system