Lovato 31RM415 Earth Leakage Relay with External Toroid

Lovato 31RM415 earth leakage relay with external toroidal transformer

The Lovato 31RM415 is a modular earth leakage relay with one operating threshold, working with an external toroidal current transformer and detecting type A residual currents. The operating current is adjustable from 25 mA to 250 A through multiplier switches, and the delay from 0.02 to 5 seconds. Seven Star LLC supplies the 31RM415 in Oman and the GCC as an independent supplier in Muscat.

The code marks the RM series and the 415 multi-voltage supply version covering 110 to 125 V AC/DC, 220 to 240 V AC and 380 to 415 V AC. The 48 V version is a separate code, 31RM48.

31RM415 technical specifications

How an earth leakage relay with a toroid works

All conductors of the circuit pass through the ring of the toroidal transformer. In a healthy circuit the vector sum of currents is zero and the transformer sees nothing. If part of the current leaks to earth, a residual current flows and the toroid delivers a signal to the relay, which compares it to the threshold IΔn and the delay. When both are exceeded, the output relay trips and opens the breaker or contactor through its shunt coil or the control circuit.

Separating the sensor from the relay is what gives the wide range. The same relay can protect a small 30 mA circuit or a large feeder at 250 A threshold, by changing the toroid size and the multiplier.

Where the 31RM415 fits

It is used where a residual current device built into a breaker is not available or its thresholds are too fixed: feeders with selectivity needs, large motors and process plants. Similar relays in the catalogue include the 31RM48, 31RMT415 and RTB series with toroids sized to the conductors. Selectivity between levels is achieved by setting a higher threshold and a longer delay on the upstream relay than on the downstream.

31RM415 selection and ordering checklist

• Select the toroid size that fits the cable or busbar bundle
• Decide the trip current and delay from the protection study
• Confirm the supply voltage among the three available bands
• Provide a shunt-trip breaker or contactor to be opened
• Decide automatic or manual reset
• Check Type A suitability for the load electronics

Installation and commissioning of the 31RM415

Pass all live conductors, including neutral but not the earth conductor, through the toroid, and keep the toroid wiring away from power cables. Set the multiplier switches, the time delay and the reset mode, and press the test button to check the output. A full injection test is recommended at commissioning. Nuisance trips usually come from neutral-earth bonds made downstream of the toroid or from cable capacitance on long runs.

Typical 31RM415 applications in Oman and the GCC

Typical uses are main distribution boards, large pump stations, desalination plants and camps. In hot, humid coastal sites insulation resistance falls, increasing leakage currents, so a threshold that is too low gives nuisance trips; choose settings with measured standing leakage in mind.

Selectivity and nuisance-trip avoidance with the 31RM415

In a graded system the relay nearest the load is set to the lowest threshold and shortest delay, and each stage upstream is set higher and slower, so that only the faulty branch is disconnected. The two time ranges, 0.02 to 0.5 s and 0.2 to 5 s, give room for three or four stages. A common rule is that the upstream setting is at least twice the downstream current and the delay is longer than the total break time of the downstream device.

Standing leakage in the Gulf can be significant on installations with many variable-speed drives, EMC filters or heating cables, because their capacitors leak a few milliamperes each to earth. Measure the natural leakage with a clamp meter before choosing the threshold, and keep the setting well above that value. The test button on the front verifies the output circuit, but it does not prove that the toroid is correctly installed, so do a periodic injection test with a known current passing through a test winding or cable.

Information to send with an RFQ for the 31RM415

• Part number 31RM415 and quantity
• Circuit current and cable size for the toroid
• Required trip current and delay
• Auxiliary supply voltage
• Breaker or contactor to be tripped
• Delivery location

Site conditions in Oman for the 31RM415

Control cabinets in Gulf plants often run hot, because many sit in outdoor kiosks or in rooms where air conditioning is not always reliable. Before you finalise the 31RM415, check the permitted ambient range and any derating stated by the manufacturer against the real temperature inside your panel, and leave the recommended spacing around the device so that heat can escape. Long cable runs between the field and the marshalling cabinet are common on large sites, so confirm the signal types, wiring limits and earthing arrangement early in the design.

It also helps to standardise on a small number of part numbers across a project. Keeping a few spare 31RM415 units on site in Oman shortens recovery time after a fault, and documenting configuration settings makes replacement faster for the maintenance team.

Documents and quotation

Send the part number 31RM415 and we will confirm the documents available for it, such as the technical data sheet, wiring diagram and instruction sheet, together with availability and lead time.

Seven Star LLC is an independent supplier in Muscat and is not an official channel of the manufacturer. Share the quantity, delivery location and project reference with the request and we will answer with a formal quotation.