Generator keeps tripping the breaker
A breaker that trips is not a fault. It is a protective device doing exactly what it was fitted to do, and it has just told you something about the set or the load that you did not know a moment ago. The job is to find out what.
Do not keep resetting it, and never fit a bigger one
A breaker that trips twice is reporting a real condition. The third reset is the one that welds contacts, cooks a winding or pushes an earth fault into a short. And the breaker is sized to protect the cable and the alternator — fitting a larger one does not give you more generator, it removes the protection from a machine that is already telling you it is in trouble.
Anything that involves opening a switchboard, taking readings on live conductors or testing insulation is work for a competent electrical person, on an isolated and locked-off board, with the set in Stop — never Auto, because an AMF panel in Auto will crank the engine the moment it decides the mains have gone.
Which protection operated?
What a breaker is actually measuring
Most generator output breakers hold two or three separate trip mechanisms, and knowing which one operated is half the diagnosis.
Thermal overload
A slow, inverse-time response to sustained current above the setting. Small overload, long delay; larger overload, shorter delay. This is the trip you get when the set is genuinely carrying more than it should for minutes at a time.
Magnetic trip
An immediate response to a very large current — a short circuit or a hard fault. It operates in a fraction of a cycle, and there is no ambiguity about it.
Earth fault protection
Where fitted. It compares current going out with current coming back and trips on the difference — current escaping to earth through insulation, moisture or a damaged cable.
The controller's own protections
A different thing entirely. Overcurrent, reverse power, current imbalance, over or under voltage and over or under frequency protections in the panel command the breaker open and log an alarm. A panel alarm tells you which protection acted; a mechanical trip with no alarm was the breaker's own trip unit.
Failed to open or failed to close on the controller means the breaker did not confirm the position it was commanded to take. That is a breaker, contactor, auxiliary-contact or wiring fault — not an electrical overload. See control panel and AVR repair.
The most useful question on this page
Narrow it by when it trips
The pattern is most of the diagnosis. Find your row.
| When it trips | What it usually means | Check, cheapest first | When to stop and call |
|---|---|---|---|
| Immediately on closing, no load connected | A fault on the generator side of the breaker, or a failed trip unit. Occasionally a shorted cable between alternator and breaker. | Confirm the load side really is dead. Check the terminal box for scorching, moisture, dust bridging or a loose conductor. Insulation resistance from windings and cables to earth. | If insulation resistance is low, stop. That is a winding or cable fault, not a reset. |
| On closing, as soon as load is connected | Earth fault, short circuit or a badly connected load. Sometimes an ATS closing onto a faulted circuit. | Open every downstream way and close them back one at a time to find the offending circuit. Insulation-test that circuit. | Once you have found the faulty circuit and it is not obvious, hand it to an electrician rather than energising it again. |
| Seconds to minutes after taking load | Genuine overload. The thermal element is doing its job. | Current on all three phases against the breaker setting and the set's nameplate. Look for what was switched on recently. | If the load is genuinely above the rating, the answer is load management or a bigger set — not a bigger breaker. |
| Only when a large motor starts | Starting inrush. A direct-on-line motor draws several times its running current at very poor power factor. | Which motor, and how it is started. Whether the short-time trip setting is too tight for the inrush profile. | If the inrush is a real problem, it is a sizing and starting-method question. |
| Under load, but only in the afternoon or in summer | Marginal loading plus heat. Breakers derate with ambient temperature, and so does the set. | Panel and plant-room temperature, ventilation, whether the trip repeats at the same time of day. | Persistent hot-weather trips on a set that copes in winter is a capacity and cooling question. |
| Randomly — no pattern, no alarm, no heat | Failing trip unit, worn breaker, a loose connection heating locally, or a controller protection set wrongly. | Thermal survey of the connections. Breaker age, condition and operating history. Controller protection settings against the set's rating. | A breaker that trips at random has lost your trust and is no longer a protective device. |
| On load rejection, or when the mains return | Reverse power or a transfer sequence fault rather than an overload. | The controller's event log and the transfer timing. | Reverse-power trips are a paralleling and transfer issue, not an overload. |
| With one phase reading very differently | Load imbalance across the three phases, or an open winding, connection or breaker pole. | Current and voltage on all three phases, phase-to-neutral as well as phase-to-phase. | A dead or weak phase on the alternator side is winding work — see alternator repair and rewinding. |
The usual suspects
Four causes account for most of them
- Genuine overloadThe most common cause, and the most commonly denied — a set that carried the load for years feels like it should carry it now. Usually it has not degraded; the load has grown. Measured current at the breaker against the nameplate settles it in five minutes. See load calculation and sizing.
- Earth fault in the downstream installationInsulation degrades. Moisture gets into an outdoor board, a cable is damaged during building work, a motor winding fails to earth. What confuses people is that the same installation may run perfectly on the mains, because the generator's neutral earthing arrangement and the utility's are not the same. A circuit can leak quietly for months and only trip the set.
- Motor starting inrushA direct-on-line induction motor draws roughly six to eight times its full-load current for the first moments of a start, at a power factor as low as 0.2 to 0.35 — a very large current and almost no useful power. The engine feels a speed dip; the breaker feels a current spike. Staged restarting, soft starters or star-delta starting solve it. A bigger breaker does not.
- The breaker itselfTrip units age. Contacts erode. Terminations loosen and heat, and a hot joint raises local resistance and current density until something operates. A breaker that has cleared a genuine short circuit has done work and may not be fit to close again without inspection. Breakers are consumable protective devices, not permanent fittings.
Local conditions
What makes this worse in the Gulf
How we approach it
Measurement first, parts second
A set that trips its breaker is a set nobody actually knows the capacity of.
The first step is current on each phase, voltage on each phase, the controller event log, the breaker's own settings against the set's rating, and insulation resistance on the alternator and the downstream circuits. That sequence separates the three possible defendants — the load, the alternator, the breaker — before anyone spends money on any of them.
Where the answer is the alternator, that is winding and excitation work. Where it is the panel or the protection settings, that is bench and configuration work. Where it is the load, we say so, which is a cheaper conversation than a repair that was never needed. And where the set is simply too small for what the building has become, that is a sizing exercise rather than a repair — better learnt from a measured test than from a dark building.
- Why the load test matters here
Very often the honest answer is that the set has never been proved at its rating, and the load grew around it while nobody was measuring.
- What it produces
A controlled load applied in steps, with voltage, current, frequency and temperatures recorded at each one.
- What it settles
"Is it the breaker or is it the generator" stops being an argument and becomes a reading.
Before you phone
What to have ready when you call
Call or WhatsApp +971 50 767 9050. The trip pattern usually tells us, before anyone drives anywhere, whether this is a load problem, a panel problem or an alternator problem.
The equipment
- The set's make, model and rating
- The breaker's rating and its settings
- What the controller's event log shows
- How many times it has been reset
The pattern — the valuable part
- On closing into a dead board?
- As soon as load is connected?
- Only when one particular motor starts?
- At random, or only in the heat of the afternoon?
Site currently dark: emergency generator repair and breakdown callout. Full symptom list: diesel generator troubleshooting. Planned work and quotations: jacob@abradiesel.com.
Common questions
Breaker trips, answered
Why does my generator breaker trip with no load connected?
Because the fault is on the generator side of the breaker rather than in the building. The usual causes are an insulation failure in the alternator windings or in the cabling between alternator and breaker, moisture or dust tracking in the terminal box, or a trip unit that has failed. Do not keep closing it — have the insulation resistance measured. A set that trips into a dead board is telling you something specific.
Can I fit a bigger breaker to stop it tripping?
No. The breaker is sized to protect the cable and the alternator, and fitting a larger one removes that protection without adding any generating capacity. If the set is genuinely overloaded, the answer is to shed load, stage the starting, or install a set that matches the load.
Why does the load run fine on the mains but trip the generator?
Two reasons, usually. The generator has a higher source impedance than the utility supply, so inrush and harmonic effects the mains absorbs without complaint show up as voltage dips and current spikes on the set. And the earthing arrangement on the generator may differ from the mains supply's, so an existing earth leakage the mains never noticed becomes a trip as soon as the set is carrying the building.
The panel says "failed to open". Is that the same as tripping?
No, and the distinction matters. A trip is a protection operating. "Failed to open" means the controller commanded the breaker to open and never saw confirmation that it did — a breaker, contactor, auxiliary-contact or wiring fault. It is a switchgear problem rather than an electrical overload.
Is repeated tripping damaging the generator?
Repeated resetting into a fault is. Each reclose onto a short circuit or an earth fault puts fault current through the windings and mechanical stress through the breaker. If the underlying condition is a winding insulation failure, resetting is how a repairable alternator becomes a rewind — see generator not producing power for the related failure path.
Do I need an electrician or a generator engineer?
Both skills, and often the same visit. The measurements that separate a load fault from a set fault are electrical work, and the follow-through — alternator, panel, protection settings, engine capacity — is generator work. Describe the trip pattern on the phone and we will tell you which one your fault is likely to be before anyone travels.
Breaker will not stay closed and the site is dark?
Call or WhatsApp. Tell us when it trips — on closing, on load, on a motor start, or at random — and what the event log says. Open 7 days, 07:00–20:00.