Trlys1B Operation With Multiple Power Sources; Dry Contacts - GE Mark VIeS System Manual

6.5.3 TRLYS1B Operation with Multiple Power Sources

6.5.3.1 Dry Contacts

When these terminal boards are used as dry contacts to switch ac voltage using circuits 01 through 06, and are simultaneously
supplied with 125 V dc power through JF1, JF2, or TB3, unless all the fuses and JPx jumpers for the relay contact being used
as a dry contact with a separate supply are removed, the separate supply will be present on the Normally Open (NO) relay
terminal. If the JPx jumpers and fuses for the ac powered dry contact are not correctly removed, it will tie the ac voltage to N
125 V dc when the contact closes. A similar situation exists for the P-125. Since most ac supplies operate with a grounded
neutral, the sum of the ac peak voltage and the 125 V dc is applied to MOVs connected between the dc and ground. In 120 V
ac applications, the MOV rating is sufficient to withstand that voltage.
When the board is also supplied with 125 V dc, the preferred solution is not to connect the circuits 01 through 06 to
ac-powered control circuits. If there is insufficient spare availability, remove both the fuses and the jumper for the contact in
use for ac switching, isolating the ac voltage on the contact circuit from the dc distribution voltage. Store the jumpers and
fuseholder caps separately to reduce the possibility of inadvertent re-installation, (for example after some maintenance
activity).
The risk of damage to the MOVs due to cross-connections between the ac and dc power systems is not limited to the TRLY,
but is present anywhere the 125 V dc is exposed to cross-connection to 125 V ac. This is including but not limited to contact
sensing in motor control centers and breaker close circuits.
146 GEH-6855_Vol_II GEH-6855_Vol_II Mark VIeS Functional Safety Systems Volume II
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