Short answer: on-delay and off-delay are the same timer seen from opposite ends. On-delay waits after the control signal is applied, then the contacts transfer; remove the signal and the contacts reset immediately. Off-delay transfers the contacts immediately when the signal is applied, and holds them there for the set time after the signal is removed. That second behaviour needs energy to keep timing with no control signal — which is why most off-delay timers require a permanent supply, and why an off-delay wired like an on-delay simply never times.
This page covers the four functions that cover most panel work, how the CHINT NTE8 range is specified, and the setting mistakes that make a timer look faulty. We are an independent trading company — not a manufacturer, and not an appointed distributor of any brand — so ratings are quoted per exact ordering code.
The functions, side by side
Every one of these is a single device with one knob and one output, and yet they behave completely differently. Read the “when does it start counting” column first — most wiring errors are a mismatch between what the fitter assumed and this column.
| Function | When it starts counting | Contact behaviour | Typical use |
|---|---|---|---|
| On-delay (delay on make) | When supply or control signal is applied | Contacts transfer after the set time; reset instantly when the signal is removed | Star-delta changeover, sequential start, bypassing an inrush, pump soft-start sequencing |
| Off-delay (delay on break) | When the control signal is removed | Contacts transfer immediately on signal, stay transferred for the set time after the signal drops, then reset | Fan overrun, lubrication pump run-on, conveyor clearing, brake release hold |
| Interval | On application of the signal | Contacts transfer at once and hold for the set time regardless of the signal; then reset | Fixed-length pulse, timed dosing, one-shot operations |
| Cycling / flasher (repeat cycle) | Immediately, then repeats | Alternates on and off for the set times while powered | Beacon or alarm flashing, anti-condensation cycling |
| Star-delta | On start signal | Star contact holds for the set time, then a short transition, then delta contact closes | Three-phase motor starting where starting current must be limited |
The off-delay row is the one that causes callbacks. In an off-delay device the timing circuit must keep running when the control signal is gone, so the device needs a supply of its own — usually a permanent L and N on the supply terminals, with the control signal on a separate input. Wire it with the supply switched by the same contactor and it will reset with the contactor, and the fan will stop dead. Before ordering, confirm from the datasheet which terminals must stay live for the timing to complete, because that differs between off-delay designs and is not something to guess from the wiring diagram on the side.
The NTE8 range, as documented
The NTE8 is a DIN-rail time relay family. Two sub-families matter at quotation stage, and they are not interchangeable on range or contact rating.
| Item | Economy types (single-function) | Multi-function types (M) |
|---|---|---|
| Standard | IEC/EN 60947-5-1 | IEC 61812-1 (time relays for industrial use) |
| Supply voltage Us | AC 24–415 V, or DC 24 V, operating at 85–110 % of Us | AC/DC 12–240 V |
| Time range | 0.1 s to 480 s, in stepped ranges selected on the device | 0.1 s to 10 days |
| Output contacts | 1NO or 1 changeover; Ith 5 A; AC-15 230 V 1 A, DC-13 30 V 1 A | 1 or 2 changeover; 16 A / 250 V |
| Life | — | Electrical ≥ 100,000 operations, mechanical ≥ 10 million |
| Certification | CE (published on the product page) | CE |
Three points follow. First, the contact rating on the economy types is pilot duty: 1 A at 230 V AC is not a contactor coil of any size, so a 40 A coil needs an interposing relay, or the 16 A multi-function version with the coil’s sealed VA checked. Second, the AC 24–415 V wide-range supply suits a mixed export order, but a DC 24 V version is a different article and must be ordered as such. Third, the stepped 0.1–480 s range is chosen on a selector, so setting accuracy is a small analogue dial: fine for star-delta, not for dosing in tenths of a second.
Star-delta: the application that punishes a bad setting
Star-delta starting is the most common reason a panel buys a time relay, and it has one parameter that is not the timer. The motor starts in star, the timer runs out, the star contactor opens, and the delta contactor closes. If the transition is too long, the motor has already decelerated and the delta contactor closes onto a spinning motor with a large current spike — which the customer hears as a bang and the contactor feels as welded tips.
So the timer setting is not the only number to get right. Three things have to line up:
- Star time long enough for the motor to reach most of its speed, which is a motor and load question, not a timer question.
- Transition gap short — typically a fraction of a second — with a mechanical or electrical interlock between star and delta contactors so they can never close together. A timer alone is not an interlock.
- Delta contactor rating sized for the delta current, not the star current, and checked against AC-3 duty at the site voltage.
If the site is on 60 Hz, the motor speed at the end of the star period is higher and the starting torque curve shifts; the same timer setting that worked on 50 Hz may be too short. That is a commissioning check, not something to copy from a previous project — the frequency question is covered in contactor coil voltage 50 Hz vs 60 Hz.
Off-delay in practice: fan overrun and pump protection
Two applications justify most off-delay timers, and both are about protecting equipment after the operator has walked away.
Fan overrun after a motor stops. A large motor keeps producing heat after the contactor opens. The fan contactor is held closed by the off-delay timer for a few minutes so the winding cools by convection instead of soaking. Wire the supply permanently, take the control signal from the run contactor’s auxiliary contact, and set the time from the motor manufacturer’s cooling curve rather than from habit.
Anti-short-cycle for a pump or compressor. The requirement here is the reverse, a minimum off time before restart, and it is usually done with a cycling or dedicated anti-short-cycle relay rather than a plain off-delay. An off-delay holds an output after the signal drops; an anti-short-cycle function blocks a new start for a set period after the last stop. Buying one and expecting the other shows up as a pump starting against a closed head.
| Symptom | Usual cause | Check |
|---|---|---|
| Timer never times, contacts stay put | Supply missing on the terminals that must stay live, or control signal on the supply terminals | Datasheet terminal function, not the wiring sketch on the label |
| Times, then resets at the wrong moment | Off-delay treated as on-delay, or supply dropped with the control signal | Which contact is holding the supply |
| Time is roughly half or double the setting | Wrong range selected, or a 50 Hz calibrated device on a 60 Hz supply | Range selector position and supply frequency |
| Contacts welded after a few months | Contact overloaded — Ith is not a switching rating | Coil VA against AC-15, or add an interposing relay |
| Setting drifts over a shift | Panel temperature, or an analogue dial that was never locked | Ambient at the DIN rail, and the dial’s mechanical stop |
Specifying one, in the order that avoids rework
Work through these in sequence and the code writes itself: the function (on-delay, off-delay, interval, cycling, star-delta); the supply (AC wide range, or DC 24 V, and whether the supply must be permanent); the time range (the shortest and longest time the process will ever need, not just today’s setting); the contact configuration; and the load the contact actually switches, in AC-15 or DC-13 terms.
One detail that quietly ruins export orders: the supply. An AC 24–415 V wide-range device covers most grids, but a 60 Hz site with a 110–127 V control circuit is a different question, and a DC 24 V system needs the DC version rather than an AC device with a rectifier assumed. Tell us the control voltage, frequency and whether it is AC or DC, and the code follows — the same discipline as the grids in voltage and frequency by country.
Two related selections usually travel with a timer order: the contactor it drives (contactors and motor control) and the overload relay protecting the motor (NR2 overload relay setting). If the timer is part of a starter, send the starter schedule rather than a list of parts, and we will return a bill of materials with interlocking and coil voltages reconciled.
FAQ
Q: What is the difference between on-delay and off-delay?
A: On-delay starts timing when the control signal is applied and the contacts transfer at the end of the time; removing the signal resets immediately. Off-delay transfers the contacts immediately and holds them for the set time after the signal is removed, which requires the timing circuit to stay powered.
Q: Why does my off-delay timer not delay at all?
A: Almost always because the supply is switched together with the control signal, so the timer loses power exactly when it should start counting. The timing circuit needs a permanent supply on its own terminals; check the datasheet terminal assignment for your exact code.
Q: Can a 5 A timer contact switch a contactor coil?
A: Not on the strength of the 5 A thermal current. Switching capability is given by AC-15 or DC-13 at the circuit voltage — for the economy NTE8 types that is 1 A at 230 V AC. Above that, use the 16 A multi-function version or an interposing relay.
Q: How accurate is a stepped analogue time range?
A: Good enough for star-delta and fan overrun, where a few percent does not change the outcome. For dosing, sampling or any sequence measured in tenths of a second, use a multi-range digital device with a stated setting error rather than an analogue dial.
Q: Is a timer enough to interlock star and delta contactors?
A: No. A timer sequences the changeover; it does not prevent both contactors closing together after a fault, a welded contact or a mis-set time. Mechanical and electrical interlocks are separate, mandatory hardware.
Q: Does the timer need to be derated for 60 Hz?
A: The contact rating is a current and voltage rating and does not change with frequency, but the timing of a motor start does — the motor reaches a different speed in the same star period. Commission the setting on site at the actual frequency.
What to send us for a quotation
Function · supply voltage and frequency, AC or DC, and whether a permanent supply is available · time range · contact configuration · the load being switched (coil VA or contactor size) · DIN-rail width available · quantity · destination country. You get unit price, packing data (pcs per carton, gross weight, CBM) and the certificate document for the exact ordering code. Request a quotation.
Related: Contactors and motor control · AC-1 vs AC-3 vs AC-4 · NR2 overload relay setting · Contactor coil 50 Hz vs 60 Hz · Voltage and frequency by country · Distribution boards · How to verify genuine product