ABB AF vs Schneider TeSys on a Noisy Generator Feed: The One Spec That Actually Predicts Survival

If you think a contactor rated for 18 A AC-3 will hold up on a generator that drops to 85 V during a load step, you're about to learn why that number alone is a trap. The myth that a contactor's AC-3 rating guarantees reliable pickup and dropout under distorted generator voltage is what kills field installations. This teardown compares ABB's AF09 electronic-coil contactor against the Schneider TeSys D (e.g. LC1D18) on a real noisy generator feed — using magnitude and proportion to show where the margin lives and where it disappears.

Dimension 1: Coil voltage tolerance – the proportion of ride-through

The generator in question: a 60 kW diesel set feeding a motor control panel. Under a 30 kW motor start, voltage at the contactor terminals can dip to 70–85 % of nominal for 200–400 ms, with harmonics from the AVR hunting. ABB AF09's electronic coil is rated for a single wide range — e.g. 100–250 V AC/DC — meaning at a nominal 240 V feed, the coil holds in down to about 100 V, a 58 % of nominal threshold. The Schneider TeSys D LC1D18, by contrast, uses a conventional solenoid coil; the datasheet lists minimum pickup at 85 % of rated control voltage, and dropout at about 60–70 % depending on temperature. At 240 V nominal, that 85 % pickup equals 204 V minimum to close, and dropout around 144–168 V. During the generator dip to ~180 V (75 %), the AF09 stays well above its dropout threshold (100 V is 42 % margin below the dip), while the TeSys D is below its pickup threshold and potentially near dropout — it may chatter or drop out entirely.

The mechanism: the electronic coil uses a switched-mode power supply that maintains a constant DC bus to the solenoid regardless of input voltage, as long as the input stays above a low floor. A conventional coil depends on peak magnetic flux proportional to the RMS voltage squared — a dip to 75 % reduces holding force by 44 %, and the spring return can overcome residual magnetism. The worked consequence: on a marginal generator, the AF contactor stays closed through the sag; the TeSys D may reopen, dropping the motor and causing a nuisance trip that may require manual reset. The reversal: if your generator is oversized (e.g. 2× the largest motor start) and voltage never dips below 90 %, the conventional coil works fine, and the electronic coil's wide range provides no benefit — it's just extra cost.

Dimension 2: Harmonic susceptibility – magnitude of distortion heating

Generator voltage is not a clean sine wave; total harmonic distortion (THD) can reach 8–12 % on lightly loaded sets, with significant 5th and 7th harmonics. A conventional solenoid coil sees higher eddy-current losses at harmonic frequencies because the magnetic circuit saturates locally, increasing RMS current and coil temperature. According to IEC 60947-4-1, contactors must operate in polluted networks, but the standard does not specify a harmonic limit for the coil. The ABB AF09's electronic coil draws a near-constant power of roughly 1–2 W; the input current is pulsed at high frequency, so the harmonic content of the generator does not translate into extra heating — the SMPS rejects frequencies above its control loop bandwidth. The TeSys D conventional coil draws, for a comparable size, about 8–12 VA (roughly 4–6 W at 240 V), and that current is sinusoidal at 50/60 Hz; harmonics increase RMS current by 10–15 % on a distorted feed, raising coil temperature by perhaps 5–10 °C. Over time, this accelerates insulation aging in the coil.

The proportion: a 50 % increase in coil losses (from harmonics) on a conventional coil may add ~3 W of heat, negligible in absolute terms but significant if the contactor is in a hot enclosure. The ABB coil's absolute loss is so low that even a doubling would be trivial. The worked consequence: on a generator feed with >8 % THD, the AF coil runs cooler and more reliably; the TeSys coil may run hotter, but still within Class F insulation limits for most applications. The reversal: in a clean grid feed (THD

Dimension 3: Pickup delay on distorted waveform – the timing factor

When a generator voltage is badly distorted (e.g. flat-topping due to rectifier loads), the zero crossing can become ambiguous. A conventional solenoid coil relies on peak voltage to pull in the armature; a flat-topped wave reduces the peak-to-RMS ratio, meaning the peak voltage may be 15–20 % lower than for a pure sine wave even if RMS is nominal. The AF09's electronic coil rectifies the input and charges a DC link; the pickup delay is dominated by the SMPS startup time (typically 10–20 ms) regardless of waveform shape. The TeSys D's pickup time, per the catalog, is about 10–15 ms on a clean wave, but can stretch to 30–40 ms on a flat-topped wave because the peak voltage may not reach the pickup threshold until near the crest. In a multi-contactor sequence (e.g. star-delta start), a 20 ms delay mismatch can cause a phase overlap, potentially welding contacts or blowing fuses. The magnitude of the risk: if your sequence relies on 50 ms between contactors, a 20 ms difference is proportionally large — 40 % of the window.

The worked consequence: on a generator with high crest-factor distortion, the ABB contactor's pickup timing is deterministic; the Schneider contactor's is waveform-dependent, increasing the chance of sequence misalignment. The reversal: in single-contactor motor-start applications (non-sequential), a few extra milliseconds of pickup delay is irrelevant. The scenario that punishes the conventional coil is only multi-step timing-critical circuits on poor waveform feeds.

Dimension 4: Auxiliary contact reliability under generator ripple

Generator voltage often contains low-frequency ripple (150–300 Hz from the AVR) that can couple into control wiring. Both contactors offer built-in auxiliary contacts, but the ABB AF09 includes one NO auxiliary rated for 6 A at 240 V. The issue: if the auxiliary contact feeds a PLC input, and the contactor chatters (even for 5–10 ms), the PLC may register a false status. The generator's ripple can cause a conventional coil to micro-chatter if the RMS voltage hovers around dropout. The ABB's constant holding force eliminates micro-chatter above its 100 V threshold. The magnitude: a 10 ms micro-chatter on a 200 ms dip is only 5 % of the event, but if it repeats each motor start, the PLC diagnostics accumulate spurious "contactor failed" alarms. The proportion of nuisance alarms is directly proportional to the number of starts — on a generator that cycles daily, that's 365 false flags per year. The reversal: if the aux contact feeds only a lamp or non-critical indication, micro-chatter is invisible and irrelevant.

Failure mode: The case where the electronic coil loses

There is a real failure mode for the electronic coil: during a severe voltage sag that drops below its minimum (e.g.

Rule-based conclusion

On a noisy generator feed where voltage dips to 70–80 % of nominal for 150–400 ms and THD exceeds 8 %, the ABB AF09 electronic-coil contactor provides a measurable ride-through advantage in holding force, deterministic pickup timing, and immunity to harmonic heating. The proportional margin (58 % hold-in vs 60 % dropout) means the ABB stays closed while the Schneider TeSys D may drop out or chatter. But the rule is not blanket: if your generator's worst-case dip is below 50 % of nominal (UVLO of the electronic coil), or if your control sequence is single-contactor and timing-insensitive, the conventional coil is adequate and cheaper. Threshold: if the minimum generator voltage at the contactor terminals during any motor start falls below 60 % of nominal for more than 100 ms, the electronic coil is the safer choice. Above that threshold, the cost trade-off tilts toward the conventional coil.