Schneider Zelio vs ABB CM: Monitoring Relay Comparison
How do Schneider Zelio Control and ABB CM monitoring relays actually differ? Both ranges measure a supply or process variable, compare it to an adjustable threshold with hysteresis and trip delay, and switch a change-over output per IEC 60255 and IEC 60947-5-1. The difference is not the physics — it is module width, how many functions live in one housing, whether an auxiliary supply is needed, fault-memory options, and, on the higher models, true-RMS versus average measurement. This article compares the two ranges function by function: three-phase supply, voltage, current, level, temperature, and selection criteria, so you can specify the right part instead of defaulting to whichever one is on the shelf.
What Separates Zelio Control from the CM Range
Zelio Control is Schneider's family name for measurement and control relays, split into three tiers: RM17 (single-function, fixed feature set per part number), RM22 (22.5 mm modular, compact), and RM35 (higher-end multifunction, wider parameter range). ABB's CM range does not split by tier the same way — it splits by function code (CM-MPS, CM-ESS, CM-ENS, CM-TCS) with width mostly fixed at 22.5 mm across the family. That single-width consistency is ABB's practical advantage in a panel with tight DIN-rail space: swapping a current monitor for a level monitor does not change the footprint.
Zelio's tiering cuts the other way. RM17TE covers three-phase phase sequence, phase loss, over/undervoltage in one part, similar in scope to CM-MPS. But RM35 adds functions RM17 does not carry at all — positive-safety level detection (RM35LV), for example, where the relay fails to the safe state on cable break or probe short, not just on the measured condition. If a spec calls for that safety behavior, the ABB catalog does not have a direct match at the same function level, and you'd need to check the CM-ENx generation currently stocked.
Three-Phase Supply Monitoring: RM17TE / CM-MPS Head to Head
Both parts check phase presence, sequence (L1-L2-L3 rotation), phase loss, and voltage window in a single 3-phase device. Both catch wrong rotation before a motor starts backwards — the output relay simply never energizes if the sequence is wrong. CM-MPS measures asymmetry as a percentage of the average phase voltage; RM17TE does the same with a fixed or adjustable asymmetry band depending on the exact reference. Neither needs external CTs for this function.
What we see in the field: asymmetry nuisance trips are almost always a wiring or supply-quality problem, not a relay defect, regardless of brand. Loose neutral, single-phasing upstream of a transformer, or an unbalanced load on one leg will trip either relay at the same physical imbalance — swapping brands does not fix a bad connection.
Formula: Voltage Asymmetry — Source: general practice, referenced by both IEC 60255 measuring-relay test methods
Asymmetry % = (Max Deviation from Average / Average Phase Voltage) x 100
| Symbol | Description | Unit |
|---|---|---|
| Max Deviation | largest difference between one phase and the 3-phase average | V |
| Average Phase Voltage | mean of the three measured phase voltages | V |
| Asymmetry % | result compared against the relay's adjustable asymmetry threshold | % |
Set the asymmetry threshold too tight on either brand and you'll chase phantom trips on a supply that is simply not perfectly balanced — most real feeders sit at 1-3% asymmetry under normal load. For the full parameter breakdown by series, see the Schneider Zelio Control RM17, RM22 and RM35 range review and the ABB CM range review.
Voltage and Current Monitoring Coverage
Single-phase over/undervoltage: RM17UB and CM-ESS/CM-SRS cover the same ground — adjustable threshold, adjustable hysteresis, adjustable delay. Current: RM35JA (Schneider) and CM-EFS (ABB) both take a signal from a built-in shunt or an external CT and trip on over- or undercurrent. Undercurrent is the setting that catches a broken conveyor belt or a pump that lost its load; overcurrent catches a mechanical jam before the motor thermal trips downstream.
Neither brand publishes identical hysteresis percentages across every part number, so this is not a spec you compare on a datasheet cover page — you check the specific model. What is consistent: both let you widen the hysteresis band on noisy supplies, and both recommend doing so before shortening the trip delay when nuisance trips show up.
Level and Temperature: Where the Ranges Diverge
Level monitoring: Schneider's RM35LV and RM35W series include the positive-safety option mentioned above; ABB's CM-ENS/CM-ENE handle standard conductive-probe level detection for pump up/down and dry-run protection but the current CM generation does not carry a direct positive-safety equivalent. If a wastewater lift station spec calls out fail-safe-on-cable-break behavior, that narrows the choice toward Schneider before you even open a current comparison sheet.
Temperature: RM35ATR (Schneider) and CM-TCS/CM-MSS/CM-MSN (ABB) both read a PTC thermistor embedded in the motor winding and trip at the reference resistance defined in IEC 60947-8. Neither reads an absolute temperature from a PTC — that function needs a PT100/PT1000 input, which both brands also offer on separate part numbers within the same family logic.
Formula: PTC Thermistor Trip Reference — Source: IEC 60947-8
Rtrip ~ 3.3 kOhm per sensor element
| Symbol | Description | Unit |
|---|---|---|
| R_trip | reference resistance at which the thermistor relay switches its output | kOhm |
| Sensor element | PTC embedded in the motor winding, wired in series if multiple | - |
This resistance reference is standard-defined, not brand-defined — Schneider and ABB PTC-input relays both switch at the same ~3.3 kOhm point because they are both reading the same IEC 60947-8 sensor characteristic, not a proprietary curve. For a deeper walk-through of thermistor wiring and motor protection, see monitoring relays for motor protection with thermistor input.
Module Width, Outputs and Fault Memory
RM17 parts run narrower in some single-function variants; RM22 and RM35 standardize at 22.5 mm, matching the CM range's fixed 22.5 mm width across almost the entire family. Output contacts: both brands offer 1 or 2 change-over (SPDT/DPDT) depending on model, and both let you choose normally-energized (fail-safe — de-energizes on fault or on loss of the relay's own supply) versus normally-de-energized logic.
Fault memory (latching) is where the two families diverge on default behavior more than on capability. Higher RM35 models and the upper CM models both offer selectable auto-reset versus manual-reset-after-fault, but the factory default differs by part number in both ranges — verify it on the specific datasheet rather than assuming the family default.
Measurement Method: True-RMS vs Average
RM35 and the upper CM parts both give a choice between average-sensing and true-RMS measurement. Average-sensing assumes a clean sine wave and is cheaper; true-RMS reads the actual waveform, which matters on a supply with VFDs, UPS units, or other non-linear loads distorting the sine. Get this wrong and the relay reads a voltage or current that does not match what a true-RMS meter shows on the same point — usually close enough on a clean utility feed, not close enough downstream of a drive.
This depends on how noisy the supply actually is. On a panel fed straight from utility with no VFDs or switch-mode loads nearby, average-sensing RM17 or entry CM parts read close enough to true-RMS that the distinction rarely matters. Add a few drives on the same bus and the gap widens fast.
Which Range to Specify
| Criteria | Schneider Zelio Control | ABB CM Range |
|---|---|---|
| Module width | varies by tier (RM17 narrowest, RM22/RM35 at 22.5 mm) | 22.5 mm consistent across most of the family |
| Tiering | RM17 / RM22 / RM35 — feature set grows with tier | flat, split by function code, not by tier |
| Positive-safety level | yes, on RM35LV / RM35W | not carried on the current CM-ENx generation |
| Three-phase self-powered option | yes, select RM17TE variants | yes, CM-MPS |
| True-RMS on upper models | yes, RM35 range | yes, upper CM parts |
| Standards | IEC 60255, IEC 60947-5-1 | IEC 60255, IEC 60947-5-1 |
If the spec sheet already names a series, match it exactly — cross-brand substitution on a monitoring relay changes the panel's UL/CE documentation trail even when the function is equivalent. If you're specifying from scratch, start from the function needed (phase sequence, voltage window, current, level, temperature), not the brand, and let the phase and voltage monitoring relay selection guide narrow the part number from there. Both brands' relays sit in the same monitoring and control relays collection, alongside thermal overload relays and motor protection circuit breakers that these relays commonly interlock with in a motor starter panel.
Frequently Asked Questions
Are Schneider Zelio Control and ABB CM relays interchangeable in the same panel footprint?
Mostly, since RM22/RM35 and CM parts both standardize at 22.5 mm DIN-rail width with similar screw-terminal layouts. Check the specific datasheet before substituting, because terminal position and output contact count still vary by part number.
Which range needs an auxiliary supply and which is self-powered?
Both offer self-powered three-phase variants (RM17TE-type, CM-MPS) that draw from the monitored lines. Single-phase voltage, current, level, and temperature variants in both families generally need a separate auxiliary supply — verify per model.
Does ABB's CM range offer the same positive-safety level detection as Schneider's RM35LV?
Not on the current CM-ENx generation. If a spec requires fail-safe behavior on probe cable break or short, Schneider's RM35LV/RM35W is the closer match; confirm against the latest CM catalog before ruling ABB out entirely.
Do both brands support true-RMS measurement?
Yes, on their higher-end models — RM35 in the Schneider range and the upper CM parts in the ABB range. Entry-level parts in both families typically use average-sensing, which is adequate on clean utility supplies but less accurate downstream of VFDs or other non-linear loads.
Can I use a PTC thermistor relay from either brand on the same motor?
Yes, as long as the motor's embedded PTC follows the IEC 60947-8 resistance characteristic, which both RM35ATR and the CM-TCS/CM-MSS/CM-MSN family are built to read. The trip reference resistance is standard-defined, not brand-specific.
Which brand should I default to if the spec doesn't name one?
Match the function first — three-phase supply, voltage, current, level, or temperature — using the selection guide, then compare fault-memory default, output contact count, and true-RMS availability on the specific part numbers both brands offer for that function.
Conclusion
Schneider Zelio Control and ABB CM cover the same functional ground with the same underlying standards. The real decision points are narrower than "which brand": module width consistency across a mixed panel, whether the application needs positive-safety level detection (Schneider's advantage today), and whether true-RMS matters because of VFDs or other distorting loads on the same bus. Start from the monitoring relay engineering guide if you need the underlying threshold, hysteresis, and delay concepts before comparing part numbers, and check phase sequence and phase failure relay behavior and three-phase voltage monitoring for the function-level detail behind the RM17TE/CM-MPS comparison above.
