How to select Multispan voltage, phase and motor-protection relays for UAE LV panels — single-phasing preventers, over/under-voltage, and motor overload, with example models and practical wiring notes.
Why protection relays matter in UAE LV panels
Across Dubai and the wider GCC, a 400 V three-phase supply rarely stays perfectly balanced. Voltage sag during peak summer loading, DEWA switching events, a blown supply fuse or a loose incoming lug can all leave a panel running on two phases, over-voltage, or a badly unbalanced set. Motors and electronic loads tolerate this poorly — a single-phased three-phase motor keeps trying to run, draws heavy current in the healthy phases and overheats within minutes. A dedicated protection relay watches the incoming supply continuously and de-energises the contactor before damage occurs. In a purpose-built distribution board or MCC, it is the low-cost component that protects the expensive one.
The main families of Multispan protection relays
Multispan, an Indian instruments maker since 1986, builds a broad range of DIN-rail and panel-mount protection relays that map cleanly onto UAE panel needs. Voltage protection relays (VPR series) cover combined over- and under-voltage plus phase-failure sensing on three-phase supplies. Single-phasing preventers (SPP) focus on phase loss, phase reversal and unbalance. Voltage monitoring relays (VMR / SVR types) add asymmetry and sequence checking for sensitive three-phase loads. On the load side, motor-protection and overload relays (OLR) sense actual motor current. Al Misbah Al Sehri is the authorised Multispan distributor for the UAE, stocking these families in Dubai as genuine, factory-sourced units.
Voltage and phase protection: choosing over/under-voltage and single-phasing relays
For a three-phase incomer, start with what you need to detect: phase loss, phase sequence, unbalance, over-voltage and under-voltage. A single-phasing preventer such as the SPP family handles phase failure, reversal and unbalance — ideal ahead of pumps, lifts and HVAC where wrong rotation or a lost phase is the real risk. Where the supply itself swings high or low, a combined voltage protection relay (VPR) trips on both over- and under-voltage with an adjustable window, typically around 340–440 V, plus a settable trip delay so momentary dips do not nuisance-trip. Look for an adjustable restart or reset delay so the load re-energises cleanly once the supply recovers.
Motor protection: overload, unbalance and stall
Voltage-side relays protect against supply faults; they do not see a mechanically overloaded motor. For that you need a current-sensing motor-protection relay (OLR family) wired through the motor cores or via CTs on larger frames. Set the relay to the motor nameplate full-load current, then use its overload, phase-unbalance and single-phasing detection to trip on locked-rotor, jammed pumps or a dropped phase under load. Multispan motor-protection relays commonly offer adjustable trip class and a start-up bypass so the relay ignores inrush during acceleration. Pair this with the voltage relay upstream: the two together cover both a bad supply and a bad load.
Reading the model codes: VPR, SVR, SPP, VMR and OLR
Multispan part numbers describe function first, then options. VPR denotes a voltage protection relay (over/under-voltage with phase failure); SVR and VMR indicate voltage/sequence monitoring variants; SPP marks a single-phasing preventer; OLR designates a current-based overload/motor-protection relay. Suffixes then define supply voltage (415 V AC three-phase is standard here), mounting (DIN rail versus panel/flush), output contact rating and whether adjustment is via potentiometer or digital display. When you request a quote, give the exact incoming voltage, the load type and current, and whether you want front-panel setting or sealed presets — that pins the right ordering code the first time.
Selection checklist and wiring notes for UAE panels
Match the relay supply voltage to your incomer (415 V AC, 50 Hz). Confirm the output contact (usually a changeover) can carry or interpose the contactor coil — for large contactors, switch through an interposing relay rather than the protection contact directly. Set the trip delay long enough to ride through DEWA switching transients but short enough to protect the motor. Wire the relay to drop out the coil circuit, not just signal, so a fault genuinely opens the contactor. For motor-protection relays, route the correct number of cable passes through the sensing window to keep small motors in the adjustable range. Allow DIN-rail width and clear front access for setting potentiometers or the display.
Building it into a complete panel
A protection relay only earns its place when it is correctly integrated — sized to the load, coordinated with the upstream breaker, and wired to actually break the control circuit. As a Dubai-based switchgear manufacturer, Al Misbah Al Sehri builds MDB, SMDB, MCC and pump-control panels to IEC and DEWA practice with Multispan protection and motor-protection relays fitted, set and tested as part of the assembly. Because we are the authorised Multispan distributor and also a genuine multi-brand supplier of ABB, Schneider, Legrand and others, the relays, contactors and breakers in one panel come from a single, accountable source. Send us the load schedule for the correct relay and panel build.
