Timing Relay Cross-Reference: Zelio RE vs ABB CT-D
How do you cross-reference a Schneider Zelio Time relay to an ABB CT-D relay? There is no manufacturer-published one-to-one table between Zelio Time (RE17, RE22, REXL) and ABB CT-D (CT-MFD, CT-ERD, CT-AHD, CT-VWD) part numbers, because the two ranges split functions and time ranges across different models even though both comply with IEC 61812 and IEC 60947-5-1. Pick the wrong equivalent and you get a star-delta transition set a beat too short, a multifunction unit missing the one range the panel actually needs, or a plug-in base that will not accept the new relay. This guide covers four checks that make a cross-reference hold up: function match, timing range and accuracy, contacts and voltage, and mounting format, plus where Zelio Time and CT-D typically line up and where they don't.
Why a Timing Relay Cross-Reference Is Not a Part-Number Swap
A contactor cross-reference is mostly about frame size, pole count and coil voltage. A timing relay adds a fourth variable that has no visual equivalent on the shelf: the function logic burned into the microcontroller. Two relays can share the same module width, the same multi-voltage supply, and still behave differently the moment power is removed mid-cycle. Swap on assumption alone and the fault shows up weeks later, usually as a sequence that drifts or a star contactor that never drops out cleanly.
What we see in the field: panel builders often cross-reference by dial label rather than by function code. A "0.1s-100h" range printed on both units looks identical, but one relay reaches that range with eight rotary steps and the other with four, and the two do not overlap at every point.
Step 1 — Match the Function Before Anything Else
Function comes first because it determines whether the relay is even a candidate. Confirm what the existing relay actually does in the circuit, not what its part number implies.
On-Delay and Off-Delay
On-delay (function A/E) energizes, waits the set time, then switches and stays switched. Off-delay (function B/R) switches immediately on trigger, then reverts the set time after the trigger clears. True off-delay needs a stored charge to time out once the supply itself is removed; a control-signal off-delay keeps its supply and times from a separate input. These are not interchangeable in a cross-reference — a control-signal off-delay substituted for a true off-delay will simply stop timing if the supply drops.
Star-Delta and Multifunction
Star-delta timers close the star contactor, time the run-up, open star, hold a short transition dead-time, then close delta. A multifunction relay (Zelio RE22, ABB CT-MFD) selects several of the above functions and several ranges from one body via rotary switches, which is useful when the exact function on-site is unclear or when stock needs to cover several applications with one SKU.
Step 2 — Match Timing Range and Repeat Accuracy
Once function is confirmed, range and accuracy decide whether the substitute holds the same tolerance the original sequence was built around. A relay rated for 0.1-10 s covers a different slice of the same "0.1s-100h" family label than one built for 1-100 h, even if both ranges appear somewhere on that family's datasheet.
Formula: Repeat Accuracy Error — Source: IEC 61812, Clause 6
Δt = ± a% × tset
| Symbol | Description | Unit |
|---|---|---|
| Δt | Maximum deviation between repeated timing cycles | s |
| a | Repeat accuracy rating printed on the relay (typically 0.5-1%) | % |
| tset | Time value dialed on the relay | s |
A cross-referenced relay with a looser repeat accuracy than the original will pass a bench test at tset and still drift over thousands of cycles. That matters for pump alternation and batching sequences more than for a single star-delta start.
Step 3 — Match Contacts, Supply Voltage and Mounting
Contact configuration (SPDT vs DPDT) and current rating set what the timer can switch directly versus through an interposing contactor coil. Multi-voltage supply bands are common on both Zelio Time and ABB CT-D, but "multi-voltage" does not mean universal — check that the panel's control voltage sits inside the printed band, not just near it.
Mounting format ends the check. DIN-rail 17.5 mm or 22.5 mm modules from one brand generally fit a standard rail regardless of manufacturer. Plug-in (11-pin or 8-pin socket) relays are a different story: pin-outs are not standardized brand to brand, so a socket-mounted Zelio REXL relay does not drop into an existing ABB socket, and the reverse is equally true. Some panel builders keep a base-agnostic terminal block wired instead, specifically to avoid this trap on repeat orders.
Zelio Time vs ABB CT-D at a Glance
| Criteria | Schneider Zelio Time (RE17/RE22) | ABB CT-D (CT-MFD/CT-ERD/CT-AHD/CT-VWD) | What to verify when cross-referencing |
|---|---|---|---|
| Module width | 17.5 mm (RE17) or 22.5 mm (RE22) | 17.5 mm across the range | Panel space and rail layout may shift by one module |
| Function coverage | Single-function (RE17) or multifunction/multi-range (RE22) | Split across CT-ERD, CT-AHD, CT-VWD, or combined in CT-MFD | One RE22 may map to two single-function ABB units, or one CT-MFD |
| Star-delta output | RE22R, two outputs with adjustable transition | CT-VWD / CT-YDD / CT-SDD, two outputs with adjustable transition | Confirm minimum transition dead-time, not just run-up range |
| Plug-in option | REXL socket-mount range | CT-D range is primarily DIN-rail; verify current ABB plug-in offer separately | Socket pin-out is not interchangeable between brands |
| Supply voltage | Multi-voltage AC/DC variants available | Multi-voltage AC/DC variants available | Confirm the exact band overlaps the panel's control voltage |
Star-Delta Cross-Reference Needs Extra Care
Star-delta substitutions fail more often than any other timing relay swap, and not because of the run-up range. The transition dead-time — the gap between opening the star contactor and closing delta — is what keeps the two contactors from bridging phases for an instant. This depends on the physical drop-out time of the specific contactors in the panel, not just the timer's rated minimum, so a cross-reference has to check the new relay's adjustable transition floor against what the existing contactors need. See star-delta timing relays for motor starting for how the run-up and transition settings interact, and browse contactors when the drop-out time of the existing units is the unknown.
Putting the Four Checks Together
In order: confirm the function, confirm the range and required accuracy, confirm contacts and voltage, confirm the mounting format. Skip a step and the failure shows up later, usually intermittently, which makes it harder to trace than a relay that simply does not fit. For a first-principles look at the full range of functions available before narrowing to a specific brand, the timing relay engineering guide covers the complete function set, and types of timing relays breaks down on-delay, off-delay and multifunction side by side.
Some panel builders standardize on one brand's multifunction range across a whole product line specifically to avoid repeating this four-step check on every replacement order. That trades a slightly higher per-unit cost for fewer cross-reference exercises down the line — a fair swap on high-volume lines, less obviously worth it on one-off panels.
Frequently Asked Questions
Is there an official Zelio Time to ABB CT-D cross-reference table?
No manufacturer publishes a one-to-one part-number table between the two ranges. Match by function, timing range, contact configuration and mounting format instead of assuming direct part equivalence.
Can an ABB CT-ERD replace a Schneider RE22 multifunction timer?
Only if the RE22 is actually configured for a single function, such as on-delay, in that application. If the panel uses the RE22's multifunction or multi-range capability, a single-function CT-ERD will not cover it — look at CT-MFD instead.
Do Zelio Time and ABB CT-D timing relays share the same plug-in socket?
No. Plug-in bases and pin-outs are not standardized across brands, so a socket-mounted relay from one manufacturer does not drop into the other's base without rewiring or replacing the socket.
What matters most when cross-referencing a star-delta timer?
The transition dead-time adjustment range matters as much as the run-up range. It has to exceed the mechanical drop-out time of the specific star and delta contactors already installed in the panel.
Does repeat accuracy affect a cross-reference decision?
Yes, whenever downstream logic depends on tight timing tolerances repeated over many cycles, such as pump alternation. A looser repeat accuracy on the replacement relay can pass a single bench test and still drift over time.
Conclusion
A reliable timing relay cross-reference between Schneider Zelio Time and ABB CT-D comes down to four checks done in order: function, range and accuracy, contacts and voltage, mounting format. Star-delta substitutions deserve extra attention to the transition dead-time specifically. Start from function, not from a part number that looks similar, and confirm each step against the actual panel rather than the datasheet alone. For guidance on picking a relay from scratch rather than replacing one, see how to select a timing relay, and browse the current timing and control relays range for stocked Zelio Time and CT-D options.
