Frequently asked questions - Over/Under Voltage MV12


Can MV12 be used for both under voltage and over voltage protection ?
Yes. MV12 is designed to work either as a under voltage relay or as an Over voltage relay. There a DIP switch inside the relay - here we can select the operation as either U/V or O/V. Please note that one MV12 can work in one mode only (ie) either as an U/V relay or an O/V relay, depending on the selection made on the DIP switch inside the relay.

What do I do if I need both U/V and O/V protection in a feeder ?
MV12 is a single phase relay.
Single phase application : If both U/V and O/V are required , you have to use two MV12 relays - one where the internal DIP switch is set for U/V mode and the other where the internal DIP switch is set for O/V mode.
Three phase application : Here you have to use 4 MV12 relays - two for connection to R & Y phases and two for connection to Y & B phases.

What are the time delays available in MV12 ?
MV12 provides bothe Definite time delay and inverse time delay - the type of delay is field selectable, by means of a DIP switch setting inside the relay. Please refer data sheet for range details.

Can I connect 415V ac as sensing voltage input to MV12.
Yes ofcourse. MV12 is designed to be used in both LT and HT applications.
LT, 3ph, 3 wire application :The line to line voltage 415V ac in a LT application can be directly connected to the measuring input terminals of MV12. There is no need for an interposing transformer between relay and the line.
LT, 3 ph 4 wire application : MV12 can accept 240 Vac as measuring input.
HT applications: MV12 will accept 110 V ac input from PT secondary.
The selection of input ( whether 110 or 240 or 415 V ac ) is done by a jumper setting inside the relay.

How long does it take to set an MV12 ?
Maximum 10 minutes. There are two settings inside the relay and three settings on the front panel.

How do I test MV12 ?
There are two methods :
1) From the front panel : There is a test push button on the front panel. After powering on the relay, please observe that only three LEDs are on. ( the U/V or O/V LED, the time characteristic LED, and the power on LED). If more than three LEDs are on, then the relay is defective.
If only three LEDs are on as above , press the Test PB. All LEDs on the front panle will glow for about two sec and go off. The relay is now functionally OK.
2) Voltage injection method : Please refer to L&T document on procedure for testing the MV12 relay by secondary voltage injection.

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