What separates Schneider Zelio Time from ABB CT-D timing relays? Both ranges are electronic, multi-voltage, DIN-rail or plug-in change-over timers covering on-delay, off-delay, multifunction, star-delta and cyclic operation, built to IEC 61812 and IEC 60947-5-1. The choice between them comes down to module width, how many functions and ranges a single part number covers, plug-in versus fixed formats, and how finely the star-delta transition can be set. This article compares module footprint, function and range coverage, transition-time granularity, accuracy, and mounting format, then gives selection guidance for panel builders stocking one line over the other.
Zelio Time and CT-D: Same Job, Different Part Structure
Schneider's timing and control relays line splits the job into three families: RE17 for single-function/compact timing, RE22 for multifunction and multi-range devices, and REXL for plug-in socket-mounted timers. ABB collapses more of that into the CT-D range itself — CT-MFD for multifunction, CT-ERD for on-delay, CT-AHD for off-delay/true off-delay, and CT-VWD/CT-YDD/CT-SDD for star-delta, with CT-S as the earlier generation. Neither company invented a new timing principle here. Both use an internal oscillator/counter driving a dial or DIP-plus-potentiometer setting, with a change-over (SPDT/DPDT) output contact rated for a few amps.
What we see in the field: panel shops that already stock Schneider contactors tend to default to RE17/RE22 for parts-bin simplicity, and ABB-heavy shops do the same with CT-D. The functional overlap is close enough that brand loyalty, not capability, usually decides the order.
Module Width and Panel Footprint
RE17 is a 17.5 mm modular timer, matching Schneider's standard single-module control-circuit width. RE22, carrying more functions and rotary range selection, is built on a 22.5 mm module — the extra 5 mm buys the added front-panel switches. ABB keeps CT-D uniformly at 17.5 mm across single-function and multifunction members, including CT-MFD. On a densely packed DIN rail, that difference matters: swapping a single RE22 for a CT-MFD reclaims 5 mm per timer, which adds up across a panel carrying a dozen timing relays.
Function and Timing-Range Coverage
RE22 and CT-MFD both put several functions — on-delay, off-delay, star-delta, flasher, interval — on one part, selected by a front rotary switch, with a second rotary switch for the time-range band (commonly spanning roughly 0.1 s to 100 h across steps). Single-function parts (RE17 on-delay/off-delay variants, CT-ERD, CT-AHD) trade that flexibility for a smaller footprint and one less thing to mis-set on the bench. REXL's plug-in socket format has no direct 17.5 mm-width CT-D equivalent from ABB in the same panel-mount style — ABB's plug-in timers are a separate product line outside CT-D proper.
Multi-range coverage cuts inventory. A control panel with three different timing needs across on-delay, interval and star-delta can, in principle, be built from one RE22 or CT-MFD part number stocked in quantity, instead of three single-function SKUs. The trade-off is a slightly more complex commissioning step: someone has to set both the function switch and the range switch correctly, and a wrong range selection reads as "the timer isn't working" on first power-up.
Star-Delta Transition Setting: Granularity Compared
Both lines offer dedicated star-delta timing relays for motor starting — RE22R on the Schneider side, CT-VWD/CT-YDD/CT-SDD on the ABB side. The function is identical in principle: close star, time the run-up (typically a few seconds to around 30 s), open star, hold a short transition dead-time in the tens-of-milliseconds range, then close delta. That transition is the number that actually matters for equipment survival, because it exists to let the star contactor's arc clear before the delta contactor lands 180° out of phase with the still-decaying motor back-EMF. Set the transition too short and both contactors overlap.
Where the ranges diverge is transition adjustability: some star-delta variants in each family give the transition a fixed factory value, others let it be dial-set independently of run-up time. Confirm the specific part's transition behavior before specifying it against a motor with a long run-up — a fixed short transition sized for a small pump does not automatically suit a heavily loaded compressor. Do not invent a transition figure for either brand here; read it off the specific datasheet for the exact reference chosen. This is one case where a contactors supplier's cross-reference sheet is worth more than a general spec comparison.
Accuracy, Repeatability and Setting Resolution
Repeat accuracy — how closely successive timing cycles match at a fixed dial setting — is typically specified as a percentage of the set value on both ranges, in the roughly ±0.5% to ±1% band common to electronic timing relays built to IEC 61812. Setting accuracy (how close the dial marking is to the actual delivered time) runs looser than repeat accuracy on most multi-range parts, because one rotary scale covers a wide band. This is the practical reason multi-range timers are read as "set roughly 8 s, verify on a stopwatch" rather than trusted to the printed graduation.
Formula: Repeat accuracy error band — Source: IEC 61812, setting/repeat accuracy clause
Terror = ± (a% × Tset)
| Symbol | Description | Unit |
|---|---|---|
| Terror | Repeat accuracy error band around the set time | s (or ms) |
| a | Repeat accuracy percentage (device-dependent, typically ±0.5% to ±1%) | % |
| Tset | Set time value on the dial or rotary range | s |
At a 60 s set point with a ±1% repeat accuracy, that error band is only ±0.6 s — trivial for a pump-alternation sequence, tight enough to matter for a fast-cycling flasher application timed in fractions of a second. Neither brand publishes materially looser figures than the other across comparable series; the accuracy question tends to be decided at the individual part number, not at the brand level.
Plug-In vs Fixed DIN-Rail Formats
Schneider's REXL sits in an 8-pin or 11-pin socket, which lets a panel builder swap a failed timer without disturbing field wiring — pull the relay, plug in a spare, done. That convenience costs a socket's worth of extra depth and a second failure point (the socket contacts themselves) compared with a fixed DIN-rail timer wired directly with a screw or spring terminal. ABB's CT-D range is built as a fixed DIN-rail module; the equivalent plug-in convenience sits outside the CT-D family proper. For a panel that gets serviced by someone without a screwdriver handy on-site, that difference in field-replaceability can outweigh the module-width and function-count comparisons above.
Side-by-Side Comparison
| Criteria | Schneider Zelio Time (RE17/RE22/REXL) | ABB CT-D (CT-MFD/CT-ERD/CT-AHD/CT-VWD etc.) | Practical implication |
|---|---|---|---|
| Module width | 17.5 mm (RE17) or 22.5 mm (RE22, multifunction) | 17.5 mm across single- and multi-function members | CT-MFD saves rail space vs RE22 for equivalent function count |
| Function coverage per part | Single-function (RE17) or multifunction/multi-range (RE22) | Single-function (CT-ERD/CT-AHD) or multifunction/multi-range (CT-MFD) | Functionally equivalent structure, different SKU naming |
| Star-delta variant | RE22R (two-output) | CT-VWD / CT-YDD / CT-SDD | Check transition-time adjustability on the specific part |
| Plug-in (socket) format | REXL, 8/11-pin socket | Outside CT-D family proper | Schneider offers a direct in-family plug-in path |
| Supply voltage | Multi-voltage AC/DC on most parts | Multi-voltage AC/DC on most parts | Comparable; confirm exact band per part |
| Output contact | SPDT/DPDT change-over | 1-2 c/o change-over | Comparable contact configurations |
| Governing standards | IEC 61812 / IEC 60947-5-1 | IEC 61812 / IEC 60947-5-1 | Same qualification basis, so ratings compare directly |
Which One to Spec for Your Application
If the panel is already built around one brand's contactors and control relays, matching timing relay brand keeps a single cross-reference sheet and one supplier relationship for the timing family — that alone is a reasonable tie-breaker when the technical specs land this close. Where it isn't already decided: pick RE22 or CT-MFD for multi-function stock reduction on new panel designs, RE17 or CT-ERD/CT-AHD single-function parts where the function is fixed and rail space is at a premium, and REXL where field technicians need to swap a timer without touching wiring. For star-delta specifically, don't shop on brand at all — shop on the transition-time adjustability of the exact part against the motor's run-up time. See our how to select a timing relay guide for the full function-first selection process, and the multifunction and multi-range timing relays article for how the rotary function/range switches actually work.
This depends on stock availability as much as spec sheets, admittedly — a marginally better-suited part that sits three weeks out doesn't beat an equivalent one on the shelf. Both families cover the same functional ground closely enough that lead time and existing panel standardization decide more orders than a datasheet comparison does.
For the underlying mechanics behind both ranges, see the timing relay engineering guide.
Frequently Asked Questions
Is ABB CT-D functionally equivalent to Schneider Zelio Time?
Yes, at the function level. Both ranges cover on-delay, off-delay, multifunction/multi-range, star-delta and cyclic operation as electronic, multi-voltage, change-over timing relays to IEC 61812. The differences are in module width, plug-in availability and part-number structure, not in the underlying timing functions offered.
Which is smaller, RE22 or CT-MFD?
CT-MFD is narrower. ABB's multifunction CT-D members hold to a 17.5 mm module width, while Schneider's multifunction RE22 uses a 22.5 mm module to accommodate its rotary function and range switches.
Does ABB CT-D have a plug-in (socket-mount) option like Schneider REXL?
Not within the CT-D range itself. Schneider's REXL is an 8-pin/11-pin socket-mounted timer inside the same Zelio Time family; ABB's plug-in timing relays exist as a separate product line outside CT-D.
Can I substitute an ABB CT-D star-delta timer for a Schneider RE22R without changes?
Check transition-time adjustability and terminal layout before substituting. Both provide the star/transition/delta sequence, but transition-setting granularity and terminal numbering differ between specific part numbers, and a like-for-like swap should be confirmed against both datasheets, not assumed.
Is Schneider Zelio Time or ABB CT-D more accurate?
Neither brand is categorically tighter. Repeat accuracy on both ranges runs in the same roughly ±0.5% to ±1% of set-value band typical of IEC 61812 electronic timers; accuracy varies by individual part number (single-function vs multi-range) more than by brand.
Do both ranges use the same mounting standard?
Yes. Both Zelio Time (RE17/RE22) and CT-D mount on standard DIN rail and are qualified to IEC 61812 and IEC 60947-5-1, so panel layout and rail-space planning use the same reference dimensions across brands.
Conclusion
Schneider Zelio Time and ABB CT-D solve the same problem with near-identical functional coverage: on-delay, off-delay, true off-delay, star-delta and multifunction/multi-range timing on DIN-rail or plug-in change-over relays. CT-MFD's flat 17.5 mm width across single- and multi-function parts is the clearest hard differentiator against RE22's 22.5 mm multifunction module; REXL's in-family plug-in format is Schneider's clearest differentiator against CT-D. Beyond that, the decision comes down to existing panel standardization, star-delta transition adjustability on the exact part number, and stock lead time — not a fundamental capability gap between the two ranges.