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Page 6 of 20 Text artwork 990-9030 Rev. A. Equipment Handbook for the Low Voltage Disconnectors series
SECTION 3: CIRCUIT DESCRIPTION
GENERAL
1 With reference to the circuit diagram in Appendix B, the units consist of a contactor and control
circuitry to connect and disconnect the input voltage to and from the output. The units are typically
used in line with a positive earth power system, between for example a power cubicle (input) and a
battery (output).
DC CONNECTIONS
2 The input voltage on the negative input terminal is fed via fuse FS1 to the contactor BC1, which is
normally closed, directly to the output at the negative output terminal. The positive common output
cable from the external power system is not connected to the units (only an auxiliary input, capable of
carrying a light current to power the LVD PCA is required).
LOW VOLTAGE DISCONNECTION
3 If the input voltage decreases to 42.5 V the contactor is de-energised and the contacts opened via a
signal from the LVD PCA, which disconnects the output. The contactor is energised and the contacts
closed, reconnecting the output when the input voltage increases to 51.5 V.
4 The remote contacts change over when the contactor is de-energised with the N/C and C terminals
(terminals 4 and 5) on TB1 being opened and the N/O and C terminals (terminals 5 and 6) being
closed.
MANUAL OVERRIDE
5 The keyswitch provides a manual override to de-energise the contactor irrespective of the input
voltage, when set to the OPEN position.
REMOTE LOOP CONTACTS
6 The REMOTE LOOP contacts on TB1 terminals 1 and 2 are normally linked and if the link is broken the
contactor is de-energised and disconnects the unit from the external equipment. When installed, this
link can be replaced by a link to a remote location which is broken when an emergency occurs.