VMR Relay: Full Form, Working, Wiring and Price in India
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A VMR (Voltage Monitoring Relay) protects three-phase motors, pumps and compressors from a bad supply: a missing phase, reversed phases, unbalanced voltage, or voltage that is too low or too high. When it sees a fault, it opens its contact and the motor contactor drops out before the motor is damaged.
This guide explains what a VMR does, how it is wired in a starter panel, how to set it, and which model to choose, with live prices for the relays we stock. Prices checked 25 October 2026. Reviewed by Amit, Voltkart.
What a VMR relay protects against
- Phase failure (single phasing): if one phase is lost, a running motor keeps turning on two phases and overheats within minutes. The VMR trips instantly.
- Phase sequence (phase reversal): if two phases are swapped, the motor runs backwards. That damages pumps, compressors, conveyors and gearboxes. The VMR stops the motor from starting.
- Voltage unbalance: unequal phase voltages make unequal currents and extra heating. Better relays let you set the unbalance limit.
- Under and over voltage: low voltage makes the motor draw more current; high voltage stresses insulation. Adjustable relays trip after a set delay so short dips do not cause nuisance trips.
How a VMR works
The relay measures the three line voltages continuously. While the supply is healthy, its output relay is energised and the normally open (NO) contact is closed, so the contactor can run. When a fault appears, the output relay drops: instantly for phase failure or reversal, and after the set delay for under/over voltage. Most models reset automatically when the supply returns to normal; some also offer manual reset.
VMR relay wiring in a DOL starter
- Take the three phases (R, Y, B) to the relay's supply/sensing terminals, after the MCB or MPCB that feeds the starter.
- Wire the relay's NO output contact in series with the contactor coil circuit, normally between the stop push button and the contactor coil.
- Power up with the motor off and check the relay's healthy LED. If it shows a phase sequence fault, swap any two incoming phases (not at the motor) and recheck.
- Set the under/over voltage, unbalance and delay (on adjustable models), then test-start the motor.
Terminal numbers differ between brands and models, so always follow the diagram printed on the relay or its datasheet. Need the rest of the starter? See the motor full-load current chart and the DOL starter kits.
Which VMR to choose (live prices)
| Model | Protects against | Adjustments | Output | Price (incl. GST) |
|---|---|---|---|---|
| Minilec S2 VMR 3 | Phase failure, phase sequence, unbalance, under and over voltage | Unbalance 4–20%, UV/OV set points, trip delay 1–10 s, auto or manual reset | 2 C/O | ₹2,019 |
| Selec 600VPR-310/520-CE | Under and over voltage, phase failure, phase sequence | Trip delay 0.2–10 s | 1 C/O | ₹1,275 |
| Selec 800PSR | Phase sequence, phase failure, phase asymmetry | Fixed (no voltage set points) | 1 C/O | ₹550 |
| Minilec S1 VMR 7 | Phase sequence (reversal) only | None | 1 C/O | ₹1,020 |
| Teknika TE-240 | Under and over voltage (3-phase) | UV/OV set points | – | ₹1,712 |
| Minilec VSP D2 | Single phasing / voltage unbalance (pumps) | Unbalance trip 30–70 V, auto/manual/remote reset | 2 C/O | ₹1,688 |
- Full protection for pumps, compressors and important motors: a relay with adjustable under/over voltage and unbalance, such as the Minilec S2 VMR 3.
- Under/over voltage with phase failure and sequence at a lower price: the Selec 600VPR.
- Only stopping reverse rotation and phase loss: a phase sequence relay such as the Selec 800PSR or Minilec S1 VMR 7.
- Agricultural and monoblock pump starters: a single phase preventer such as the Minilec VSP D2.
Compare all models in the protection relay price list. Voltkart is an authorised Minilec and Selec distributor and supplies every relay with a GST invoice. Not sure which one replaces your old relay? WhatsApp us a photo of its label.
VMR relay FAQs
What is the full form of VMR?
VMR stands for Voltage Monitoring Relay. It is also called a voltage protection relay or phase failure relay. It watches the three-phase supply and switches off the motor starter when the supply goes outside safe limits.
What does a VMR relay protect against?
A three-phase VMR trips on phase failure (single phasing), wrong phase sequence (phase reversal), voltage unbalance between phases, under voltage and over voltage. Simpler models cover only phase sequence and phase failure, so check which faults each model detects.
Where is a VMR connected in a motor starter?
The three supply phases (R, Y, B) are connected to the relay's sensing terminals, after the MCB or MPCB. The relay's normally open output contact is wired in series with the contactor coil, usually next to the stop button, so the contactor drops out when the relay trips. Always follow the terminal diagram printed on the relay.
What is the price of a VMR relay in India?
On Voltkart, three-phase voltage monitoring and phase relays cost from ₹550 to ₹2,019 including GST (prices checked 25 October 2026). Phase-sequence-only relays are the cheapest; relays with adjustable under/over voltage, unbalance and two changeover contacts cost more.
Is a VMR the same as an overload relay?
No. An overload relay protects the motor from too much current caused by the load. A VMR protects it from a bad supply: missing phase, reversed phases, unbalance or wrong voltage. Most pump and compressor panels use both.
Do I need a VMR if I already have an MCB or MPCB?
Yes, for three-phase motors. An MCB or MPCB trips on short circuit and (for an MPCB) overload, but it does not trip when one phase is lost or the phases are reversed. A VMR covers those faults.