Schneider Zelio Control RM17, RM22 and RM35: Full Range Review
What is the Schneider Electric Zelio Control range? Zelio Control is Schneider's family of DIN-rail measuring and monitoring relays, built to IEC 60255 and IEC 60947-5-1, covering three-phase supply, voltage, current, level and temperature monitoring. Picking the wrong tier means either paying for functions a panel never uses or running out of channels and adding a second relay mid-build. This review walks through RM17 (single-function), RM22 (compact 22.5 mm), and RM35 (multifunction, positive-safety options), how their thresholds and hysteresis work, and where each one fits against a monitoring relay engineering guide level of detail.
RM17 — Single-Function Measurement and Control
RM17 is the base tier: one relay, one job. RM17TE is the three-phase supply controller — phase sequence, phase loss, and over/undervoltage in a single 17.5 mm module, drawing its own measurement directly from the three-phase lines. RM17UB does single-phase voltage (over, under, or window). RM17TG and the current-sensing variants round out the range for panels that only need one function per DIN-rail slot.
The trade-off is module count. A panel needing phase sequence protection on the incoming supply and separate undercurrent detection on a pump motor takes two RM17 units, not one. What we see in the field: RM17 gets specified when the panel builder already knows exactly one fault mode matters and wants the cheapest, smallest part that does it — nothing more.
RM22 — Compact 22.5 mm Modular Range
RM22 keeps the same one-relay-one-job philosophy as RM17 but widens the physical module to 22.5 mm, which is where Schneider fits a larger terminal block and, on some variants, a second measured channel. RM22TR covers three-phase supply plus voltage and current on one part number — a step toward combining functions without moving to the multifunction RM35 tier. RM22LG and RM22LA are the level-monitoring members, reading conductive probe signals for pump control and dry-run protection.
RM22 sits between RM17 and RM35 on both price and function count. It suits retrofits where the DIN-rail layout was designed around 22.5 mm slots already occupied by contactors or motor protection circuit breakers, so matching module width simplifies the layout drawing.
RM35 — Multifunction and Positive-Safety Range
RM35 is where Schneider consolidates functions into fewer parts. RM35TF is the multifunction three-phase relay — sequence, loss, asymmetry, over/undervoltage together, adjustable per parameter. RM35UA handles voltage, RM35JA current, RM35ATR temperature and thermistor input, and RM35LV/RM35W level monitoring, the latter with a positive-safety mode: the output relay de-energizes on loss of liquid signal or loss of auxiliary supply, so a wiring fault fails toward the safe state rather than silently doing nothing.
This tier costs more per unit but fewer units get specified overall. A three-phase supply panel that would need an RM17TE for sequence/loss and a second RM17UB for voltage window collapses into one RM35TF. Selectable fault memory (latching) is available on higher RM35 models — useful where an intermittent fault needs to stay flagged until someone acknowledges it, rather than auto-resetting once the quantity returns inside the window.
Setting Threshold and Hysteresis Across the Range
All three tiers share the same three adjustable parameters: threshold, hysteresis, and trip delay. The threshold is the setpoint the measured quantity must cross. Hysteresis is the reset band below (or above) that threshold that stops the output chattering when the signal sits right at the edge. Trip delay rides through a transient — a 200 ms voltage dip on motor start, for example — without tripping on something that clears itself.
Formula: Reset threshold from hysteresis — Source: IEC 60947-5-1, adjustable-relay setting practice
Vreset = Vtrip × (1 − H%)
| Symbol | Description | Unit |
|---|---|---|
| Vtrip | Set threshold at which the output switches | V (or A, depending on function) |
| H% | Hysteresis, set as a percentage of the threshold | % |
| Vreset | Value the quantity must return to before the output resets | V (or A) |
Set the hysteresis too tight and a noisy supply chatters the output on and off across the threshold; too wide and the relay tolerates a fault window that is bigger than the connected equipment can stand. This is field-tuning, not a factory-default number — a generator feeding a sensitive drive line needs a narrower band than a compressor circuit that just needs to shut off when the supply is clearly wrong.
Comparing RM17, RM22 and RM35
| Criteria | RM17 | RM22 | RM35 |
|---|---|---|---|
| Module width | 17.5 mm | 22.5 mm | 22.5 mm |
| Functions per unit | Single | Single, some combined (e.g. voltage + current) | Multifunction (sequence, loss, asymmetry, over/under together) |
| Auxiliary supply | Not needed on three-phase variants (self-powered from measured lines) | Depends on variant | Depends on variant; higher models offer wider aux ranges |
| Fault memory / latching | No | Limited | Selectable on higher models |
| Typical use case | One fault mode, cost-driven panels | Retrofits matching existing 22.5 mm layout, light multi-parameter needs | Consolidated protection, positive-safety level applications |
Choosing the Right Zelio Control Relay
Start from the fault mode, not the part number. If the panel only needs to block a motor from starting on reversed phase rotation, RM17TE alone does the job — adding RM35 multifunction capability there is paying for parameters the panel never reads. If the same incoming supply also needs asymmetry monitoring and a latched fault indication for maintenance staff, RM35TF replaces what would otherwise be two or three RM17 units.
For level and temperature, the decision is less about tier and more about sensor type: conductive probe level sensing points to RM22LG/RM22LA or RM35LV/RM35W (positive-safety), while thermistor-embedded motor windings point to RM35ATR. See temperature monitoring relays for how PTC and PT100 inputs differ. For voltage and phase decisions specifically, the selection logic is covered in how to select a phase and voltage monitoring relay, and threshold/hysteresis tuning in how to set a voltage monitoring relay.
Panels combining monitoring relays with switching hardware should size the downstream contactors to the load, not the relay — the Zelio Control output contact only drives the contactor coil, it does not carry motor current itself. Background on that boundary is in what is a monitoring relay and how it works.
Where This Fits in a Panel Design
Most panels combine a phase-sequence/loss check on the incoming supply with function-specific monitoring downstream — see phase sequence and phase failure relays for how that first check is normally wired, and three-phase voltage monitoring for asymmetry and window detection specifically. Zelio Control's whole range — RM17 through RM35 — sits in the broader monitoring and control relays category alongside ABB's CM series and other stocked equivalents.
Some panel builders standardize on RM35 across every job to cut the number of distinct part numbers they stock, accepting the higher unit cost as a trade for fewer SKUs and faster spares turnaround. Others stay on RM17/RM22 and keep unit cost down on high-volume repeat panels where the fault mode never changes. Neither is wrong; it is a stocking-strategy call, not a technical one.
Frequently Asked Questions
Can RM17 relays run without an auxiliary power supply?
The RM17TE three-phase supply variant draws its measurement power directly from the three-phase lines it monitors, so no separate auxiliary supply is required. Single-phase voltage and current variants may still need one depending on the specific part — check the wiring diagram for the exact model before assuming self-powered operation.
What is the difference between RM22 and RM35 for three-phase monitoring?
RM22TR combines three-phase supply, voltage and current in a compact 22.5 mm module but with fewer adjustable parameters than RM35TF. RM35TF is the multifunction option — sequence, loss, asymmetry, and over/undervoltage individually adjustable, plus optional fault memory on higher models.
What does positive-safety mean on RM35 level relays?
Positive-safety means the output relay de-energizes on loss of the monitored liquid signal or loss of auxiliary power, driving the circuit toward its safe state rather than staying energized through a wiring fault. RM35LV and RM35W offer this mode for dry-run and level protection.
Do Zelio Control relays interrupt motor current directly?
No. The relay's output contact (SPDT or DPDT) switches a low-current control circuit — typically a contactor coil, PLC input, or alarm — not the motor's main power. The contactor or breaker downstream does the actual current interruption.
How do I choose between RM17, RM22 and RM35 for a new panel?
Count the fault modes the panel needs to catch on one supply or load. One fault mode, cost-sensitive: RM17. Matching an existing 22.5 mm layout or needing a light combination of functions: RM22. Multiple combined functions, latching, or positive-safety level protection: RM35.
Conclusion
RM17, RM22 and RM35 are not three unrelated products — they are the same measurement and threshold logic packaged at three levels of function density. RM17 keeps cost per function lowest for panels with one clear fault to catch. RM22 matches 22.5 mm layouts and adds light combination. RM35 consolidates multiple functions, adds fault memory and positive-safety options, and reduces part-number count on panels where protection requirements grow over time. The right choice comes from the fault modes the panel actually needs to catch, not from defaulting to whichever tier was used last time.
