How to Install and Wire a Voltage Monitoring Relay
This article covers Trumeter VMR01, VMR02 and VMR03 relays for nominal 208–480 VAC, three-phase, three-wire supplies. Use it alongside the wiring diagram for your exact model. These instructions do not cover single-phase relay installations.
Before you begin
Installation must be carried out by a qualified electrician. Isolate and lock out all supplies, including any separate control supply, and verify that the circuit is de-energized before wiring. These relays reset automatically; the control system must prevent an unsafe restart when a fault clears.
Choose the right model
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Model |
Monitoring functions and adjustments |
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Phase loss and sequence; adjustable under- and overvoltage thresholds; fixed 10% asymmetry detection; adjustable trip delay. |
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Phase loss and sequence monitoring with fixed timing. No adjustable under- or overvoltage thresholds. |
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Phase loss and sequence; adjustable 5–15% asymmetry detection and trip delay. No adjustable under- or overvoltage thresholds. |
Confirm the supply frequency, operating range, required protection and output load against the documentation for the selected model. A phase monitor does not replace the equipment’s overload or short-circuit protection.
Mount and terminate the relay
Secure the relay to a 35 mm DIN rail or use the documented base-mounting arrangement. Install it in an enclosure suited to the location and keep it within its temperature, humidity and vibration limits.
Use the conductor sizes and tightening torque specified for the supplied unit. If the unit markings and documentation disagree, ask Trumeter to confirm the correct requirements before wiring.
Connect the three monitored phases
Connect the phases to L1, L2 and L3 as shown in the manual. The relay is powered from the supply it monitors. Its input diagram has no neutral connection. Measure and verify the line-to-line supply; do not confuse a phase-to-neutral reading with the system voltage.
Confirm the phase sequence against the machine design. Any wiring correction must be made with the circuit isolated, followed by the required equipment rotation check.
Connect the control output
The output is one changeover contact. It does not generate a control voltage. Connect it to the control circuit using the required control supply and the correct contact pair:
- 15 is common. In the de-energized state, 15–16 is closed and 15–18 is open.
- When the relay energizes under healthy supply conditions, 15–18 closes and 15–16 opens.
Use the contact to enable a suitably rated contactor or signal a control input, as appropriate. Check the load type, voltage, running current and inrush against the applicable contact rating. A resistive rating alone does not establish suitability for a contactor coil, motor or low-current PLC input.
Set the available controls
On VMR01, select the correct nominal voltage before setting the under- and overvoltage limits. The manual limits the usable adjustment range at some nominal voltages, so do not assume every dial setting is available across the full supply range.
On VMR03, set the asymmetry threshold for the equipment. Set an adjustable trip delay only where provided. A trip delay determines how long an applicable fault can persist before the output drops out; it is different from the delay before the output energizes. Use the model’s timing diagram because phase faults may have different response times.
Check operation before returning to service
With power isolated, check terminal selection, conductor security, exposed strands, settings and output wiring. Then energize the system under a controlled commissioning procedure and confirm the healthy indication and expected output state after the applicable delay.
Verify the fault response and recovery using suitable test equipment and an approved procedure with the machinery safely controlled. Do not create a phase fault by disconnecting a live conductor. Record the settings, measured voltages and test results, and confirm that automatic recovery cannot restart equipment unexpectedly.
For model-specific diagrams and instructions, use the VMR instruction manual. For application help, contact Trumeter Technical Support.