Best Monitoring and Measuring Relay Brands Ranked

04 Aug, 2026
Posted by: Muhammet KUL

Which brand builds the best monitoring relay? No single brand wins outright — Schneider Electric Zelio Control, ABB CM, Siemens SIRIUS and Finder 70/71/72 all meet IEC 60255 and IEC 60947-5-1, and the real differences sit in module width, how many functions combine in one device, whether an auxiliary supply is needed, and fault-memory options on the higher ranges. Rank a brand on unit price alone and a panel builder ends up stacking two relays where one multifunction unit would do. This guide ranks the stocked options by function coverage, width, aux-supply dependency, and application fit across three-phase supply, voltage, current, level, temperature and insulation monitoring.

Ranking Criteria: What "Best" Actually Means Here

Four criteria decide the ranking, not brand reputation. Function coverage — does one device handle phase sequence, phase loss, and asymmetry together, or do you need three separate relays? Module width — 17.5 mm and 22.5 mm DIN-rail footprints both exist across brands, and a tight enclosure can force the choice. Auxiliary-supply dependency — some three-phase monitors draw power straight from the measured lines and need no separate 24 VDC or 230 VAC feed, which removes a failure point and a terminal pair. Fault memory and reset mode — automatic reset suits an unattended pump station, manual (latched) reset suits a motor start circuit where an operator should see and acknowledge the fault before restarting.

Key takeaway: Before comparing brands, decide whether the application needs one multifunction relay or several single-function ones — that decision changes the ranking more than any brand preference does.

Fault memory (latched output) holds the tripped state after a fault clears until an operator manually resets the relay, instead of resetting automatically once the measured quantity returns inside the window (per IEC 60947-5-1 control-circuit device practice).

Schneider Electric Zelio Control — Broadest Range, Familiar to Most Panel Shops

The Zelio Control line covers three tiers. RM17 is single-function: RM17TE handles three-phase supply control (sequence, loss, over/undervoltage) in one device, RM17UB covers single-phase voltage, RM17TG and current-sensing variants round out the range. RM22 is the compact 22.5 mm modular tier — RM22TR for three-phase voltage and current, RM22LG/RM22LA for level. RM35 is the higher-end multifunction tier: RM35TF combines three-phase functions, RM35UA does voltage, RM35JA does current, RM35LV/RM35W cover level with positive-safety switching, and RM35ATR reads PTC thermistor temperature. All three tiers share adjustable threshold, hysteresis, and trip delay with SPDT or DPDT output contacts on DIN rail.

What we see in the field: RM17TE and RM35TF are the two SKUs procurement teams reach for first, because they cover the largest share of motor-protection and pump-panel jobs with a single part number. The tradeoff is that RM35 multifunction units cost more per unit than stacking two RM17 single-function relays — worth it only if panel space or wiring time is the constraint.

ABB CM Range — No Auxiliary Supply on the Phase Monitors

ABB's CM range splits by function rather than by tier. CM-MPS and CM-MPN monitor three-phase supply — sequence, failure, asymmetry, over/undervoltage — and CM-MPS specifically needs no auxiliary supply; it powers itself from the measured three-phase lines, which removes one control-circuit dependency in a compact panel. CM-ESS and CM-SRS handle single-phase current (over/under), CM-EFS extends current sensing, CM-ENS and CM-ENE cover liquid level, CM-TCS/CM-MSS/CM-MSN read temperature and PTC thermistor inputs, and CM-UFD/CM-UFS combine voltage and frequency monitoring in one device. All are 22.5 mm DIN-rail modules with 1-2 change-over outputs and adjustable thresholds; the higher models add selectable fault memory and a choice of true-RMS or average measurement.

True-RMS measurement calculates the actual root-mean-square value of a distorted (non-sinusoidal) waveform, rather than assuming a clean sine wave — it matters on supplies with VFD-driven harmonic distortion, where an average-sensing relay can misread the true voltage or current.

For a panel with no spare 24 VDC terminals, CM-MPS's aux-supply-free design is a real advantage over an RM17TE that needs its own feed. For a panel already running true-RMS metering elsewhere, matching measurement method across devices avoids reading mismatches during commissioning.

Siemens SIRIUS and Finder — Equivalents Worth Stocking as Lead Time Requires

Siemens SIRIUS 3UG4 and 3RR2 cover three-phase and voltage monitoring, and 3RS covers temperature, at the same functional level as Zelio Control and CM — adjustable threshold, hysteresis, change-over output, DIN-rail mount. Finder's 70/71/72 series is the third equivalent line, again meeting IEC 60255/60947-5-1 for the same core functions. Neither is a better or worse engineering choice than Schneider or ABB on spec sheet alone; the practical driver is which brand's distributor stock and lead time fits the project schedule when the primary choice is backordered.

Key takeaway: Specify by function and standard (IEC 60947-5-1, adjustable hysteresis, change-over output count) rather than by brand part number, and Schneider, ABB, Siemens or Finder can substitute without a redesign.

Insulation Monitoring Devices: A Narrower Field, Led by Bender and ABB

Insulation monitoring is a different product category from the voltage/current/level/temperature relays above — an IMD per IEC 61557-8 continuously measures insulation resistance to earth on an unearthed (IT) system and alarms on the first fault, before a second fault turns dangerous. Fewer brands compete here. Bender is the specialist, with the broadest IMD range across medical IT, marine, and industrial applications. ABB also supplies IMDs that integrate with its wider CM and protection lineup, which suits a panel that is already standardized on ABB elsewhere. Schneider's IMD presence is comparatively thin, so a hospital or marine IT-system panel typically pulls from Bender or ABB rather than Zelio Control.

Function Coverage Comparison

The table below lines up the three-phase supply monitor from each brand — the single most commonly specified monitoring-relay function — against module width, aux-supply need, and standard.

Criteria	Schneider RM17TE	ABB CM-MPS	Siemens 3UG4
Function	Sequence, loss, over/undervoltage	Sequence, failure, asymmetry, over/undervoltage	Sequence, loss, over/undervoltage
Module width	17.5 mm DIN	22.5 mm DIN	22.5 mm DIN
Auxiliary supply	Self-powered from measured lines	Self-powered from measured lines	Self-powered from measured lines
Output contacts	1 c/o (SPDT)	1-2 c/o	1 c/o (SPDT)
Standard	IEC 60947-5-1	IEC 60947-5-1	IEC 60947-5-1

Read past the row-by-row match: the real gap between brands opens up on the higher-end multifunction units (RM35TF, CM-UFD, SIRIUS 3RR2), where fault-memory options, true-RMS measurement, and how many separate functions combine in one housing start to diverge.

How to Match a Brand to an Application

Start from the fault the relay has to catch, not the brand. A motor that must never run backwards needs phase-sequence detection — RM17TE, CM-MPS, and 3UG4 all qualify equally. A dry-running pump needs either undercurrent sensing on the motor feed or conductive level sensing in the tank; not every three-phase monitor has a current input or an electrode terminal, so that requirement narrows the field fast. A hospital IT panel needs an IMD per IEC 61557-8, which rules out the general-purpose voltage/current lines entirely.

Hysteresis is the setting most often left at default and the one most worth checking regardless of brand, because a threshold set too tight relative to supply noise causes nuisance tripping no matter whose name is on the relay.

Formula: Reset Threshold from Trip Threshold and Hysteresis — Source: General monitoring relay setting practice (IEC 60947-5-1 context)

V_reset = V_trip x (1 - H%)

Symbol	Description	Unit
V_trip	Set trip threshold (over or under)	V or A
H%	Hysteresis setting, the reset band	%
V_reset	Value the quantity must return to before the output resets	V or A

Widen the hysteresis band and the relay resets less readily around the threshold, at the cost of a slower response to a real, sustained fault. This tradeoff plays out identically on Schneider, ABB, Siemens, and Finder hardware — the setting matters more than the badge.

Key takeaway: Rank brands on function coverage and standard compliance for the specific fault you need to catch; once two or three brands qualify, lead time and existing panel standardization should decide the rest.

For deeper background on how these relays work internally, see the monitoring relay engineering guide and what a monitoring relay is and how it works. For the function-by-function breakdown referenced above, see types of monitoring relays. Monitoring relays typically work alongside a motor protection circuit breaker feeding the motor and a thermal overload relay on the contactor coil — see the thermal overload relay engineering guide for how the two protection layers divide responsibility. Browse the full monitoring and control relays range for stocked Schneider and ABB part numbers.

Frequently Asked Questions

Is ABB or Schneider better for monitoring relays?

Neither is categorically better. ABB CM-MPS self-powers from the measured lines and covers asymmetry in the base three-phase model; Schneider RM17TE covers sequence, loss, and voltage in a narrower 17.5 mm width. Match the function list to the fault you need to catch, then pick whichever brand your distributor stocks with the shorter lead time.

Can I substitute Siemens or Finder for a Schneider or ABB monitoring relay?

Yes, at the function and standard level. If both relays meet IEC 60947-5-1, offer the same adjustable threshold, hysteresis and trip delay, and the same output contact count, the substitution is a like-for-like swap. Terminal layout and DIN-rail width may differ, so re-check the panel drawing before wiring.

Which brand makes the widest range of monitoring relays?

Schneider Zelio Control has the deepest catalog across three tiers (RM17, RM22, RM35), covering single-function and multifunction devices at multiple price points. ABB's CM range is comparably broad but organized by function rather than by tier.

Do I need a separate auxiliary supply for every monitoring relay?

No. Three-phase supply monitors such as ABB CM-MPS and Schneider RM17TE draw power from the measured lines and need no separate feed. Single-phase voltage, current, level, and temperature relays generally do need an auxiliary supply, since they only see one measured quantity, not a three-phase source they can draw power from.

Which brand should I use for insulation monitoring on a hospital IT system?

Bender is the specialist for medical IT insulation monitoring under IEC 61557-8, with the widest IMD range for that application. ABB also supplies IMDs that integrate with its broader CM and protection lineup where a panel is already standardized on ABB.

Conclusion

There is no universal best brand for monitoring relays — there is a best-fit device for the fault you need to catch. Schneider Zelio Control offers the deepest catalog across three tiers. ABB CM offers aux-supply-free three-phase monitoring and true-RMS options on higher models. Siemens SIRIUS and Finder are functionally equivalent substitutes worth stocking as lead time requires. Bender and ABB lead insulation monitoring specifically. Rank by function coverage, module width, auxiliary-supply dependency, and standard compliance first; brand loyalty and unit price are tiebreakers, not starting points.