What you will see
- Some circuits lose power while others remain on.
- The inverter reports a phase, grid-voltage or grid-availability warning.
- Solar generation stops despite sunshine.
- The problem appears during a supply disturbance or after electrical work.
Why it happens
Three-phase inverters monitor the incoming grid. Solis describes shutdowns associated with abnormal phase conditions, including grid imbalance. The cause may be the incoming supply, but local connections and cabling can also produce a phase-related fault.
Loss of power in one section of a building is therefore a symptom to investigate, not proof of a utility-side phase failure. An installer must establish whether the problem is upstream of the property, within its distribution system or at the inverter connection.
For a hybrid installation, also distinguish grid-connected generation from backup operation. Backup availability depends on the system’s capability, configuration and available energy. A phase warning should not be taken as a guarantee that every affected circuit will transfer to backup.
Record what remained operational. For example, tell us whether the inverter’s designated backup circuits continued working while other circuits failed, or whether all solar-supported circuits stopped together.
One phase down, inverter stops
Healthy supply
One phase missing
- 1Utility supply upstream of the property.
- 2Building distribution within the property.
- 3Inverter connection cabling and terminals.
This page is about a phase that is missing or wrongly connected. If all three phases are present but carry very different loads or voltages, that is phase imbalance, covered in phase imbalance with solar.
What the inverter phase loss error means
A three-phase supply has three live conductors (often called R, Y and B, or L1, L2 and L3) plus neutral. A three-phase inverter feeds all three at once, so before connecting, and every moment while running, it checks the voltage and frequency on each phase. If one is missing or far outside the allowed range, the inverter must stop exporting. Different brands show this differently:
- Phase loss, grid phase loss, or "grid lost" on one phase
- G-PHASE or grid phase abnormal (Solis uses "G_PHASE" when the grid phases are unbalanced or abnormal at start-up)
- Abnormal grid voltage (Huawei's manual for the SUN2000-30/33/40KTL lists alarm 301 for, among other causes, a grid outage, a disconnected AC circuit or a breaker that is off, and for large differences between phase voltages)
- Grid phase fault or phase sequence error
A tell-tale sign of a missing phase: some lights and fans in the house still work, others do not, and three-phase machines refuse to start or hum. The inverter shows a fault even though "the light has not gone".
Phase sequence error inverter: what that means
Phase sequence (or phase rotation) is the order in which the three phases reach their peak. If two phases are swapped at the meter, the main board or the inverter terminals, the order reverses. Many grid-tied inverters measure the phases individually and are not affected; some models, especially hybrids and parallel systems that form their own three-phase output, check the sequence and raise an error. Solis lists AC cables wired in the wrong sequence as one cause of its G_PHASE alarm. A swapped sequence also makes three-phase motors run backwards, so it is often noticed on a water pump or machine first.
Phase loss
Supply
One phase missing from the grid
Breaker
One pole tripped
Quick-check table: three phase inverter one phase missing
| Symptom | Likely cause | Safe owner check | Call an engineer if... |
|---|---|---|---|
| Inverter shows phase loss; some rooms dark, others lit | DISCO pole or transformer fuse blown on one phase | Check whether neighbours on the same supply have the same problem | Neighbours are fine and your phase is still missing |
| Phase loss started after storm or rain | Fuse, jumper or service cable fault on the DISCO side | Note the time and weather; do not go near the pole | DISCO says supply is fine at the meter |
| One pole of the main breaker or changeover feels different, or a breaker has tripped | Tripped or faulty breaker pole | Look at breaker handles by eye | Any breaker trips again, or is warm or discoloured |
| Phase loss on generator only | Generator phase or AVR fault, or ATS contact | Note whether it happens on grid too | Always, for generator setups |
| Phase sequence error after meter change, rewiring or new connection | Two phases swapped | Check whether any three-phase motor now runs backwards | Always; sequence correction is engineer's work |
| Grid phase fault comes and goes at certain hours | Weak or overloaded DISCO supply, loose connection heating up | Note the times; see if heavy local loads start then | It repeats daily or you see heat marks |
| Phase fault on one of three single-phase units in a parallel set | Wrong phase setting or missing phase on that unit | Note which unit shows the fault | Always |
Safety first
Safety box. Never touch the meter, the service cable, pole fuses or any DISCO equipment. These are live and belong to the DISCO. Do not open your main DB or the inverter. When a phase is missing, switch off three-phase motors and machines at their own switches: a motor running on two phases can overheat and burn. If you smell burning or see heat marks on a breaker or cable, keep away and call a qualified engineer; see burning smell from inverter or solar system.
Safe owner checks, step by step
- Photograph the inverter screen and note the exact alarm, the time and which phase it names, if any.
- Read the three phase voltages on the inverter screen or app (view only). A missing phase will read zero or very low.
- Walk through the house. Which rooms or appliances work and which do not? This often shows which phase is down.
- Ask neighbours on the same supply whether they have lost a phase too. If yes, it is almost certainly a DISCO fault.
- Report to your DISCO (FESCO, LESCO or your local company) through its complaint line or app, and tell them one phase is missing.
- Look at your own breakers by eye. If the main breaker or a changeover is part-tripped, note it. You may reset a tripped breaker once; if it trips again, leave it and call. See solar breaker tripping.
- Switch off three-phase motors until all phases are back.
- Let the inverter reconnect on its own when the phase returns; most wait for the grid to be stable first. If it stays in fault with all three phases back, restart only in the manufacturer's order; see how to restart a solar system safely.
- Send photos and notes to your installer, especially if the fault keeps returning.
What an engineer will check
- Voltage on each phase at the inverter terminals, the main board and the meter outlet, to find where the phase is lost.
- Loose or burnt connections: meter outgoing terminals, breaker terminals, cable lugs, busbars. A loose connection can heat up and drop a phase only under load.
- Breakers and changeover: a failed pole in an MCCB or changeover switch is a common hidden cause.
- Phase sequence with a phase rotation meter, and correction at the right point if two phases are swapped.
- AC cable size and quality. Solis notes that undersized or poor cable that overheats, and loose AC terminals, can trigger phase alarms.
- Grid quality: if the DISCO supply sags or one phase is weak, especially near large industrial loads, the engineer records it so you can take it to the DISCO with evidence.
- Inverter settings: grid code and phase settings, particularly on parallel or three single-phase setups. See parallel inverter error.
- Generator output if the fault happens on generator. See generator not working with inverter.
How to prevent phase loss problems
- Keep connections tight. Thermal checks of the main board and meter area during maintenance catch loose lugs before they fail.
- Use correctly sized AC cable and breakers for the inverter's output.
- Protect three-phase motors with a phase-failure relay so they stop if a phase drops.
- Plan the connection properly when converting to three-phase for net billing. See single-phase to three-phase connection.
- Choose the right inverter for the site. Our guide to three-phase vs single-phase inverters explains how each behaves when a phase is lost. For factories, see industrial and commercial solar.
- Report repeat DISCO faults in writing, with dates and photos, so there is a record.
Related grid problems are covered in inverter grid fault during load-shedding and grid voltage rise on sunny afternoons. All symptoms are listed in our solar troubleshooting guide.
How Solar Works Pakistan helps
For systems we install, our own engineering team handles after-sales complaints. WhatsApp 0336 666 4321 with a photo of the inverter screen showing the alarm and phase voltages, plus the inverter model. We target sending service personnel within 48 hours of a registered complaint to begin diagnosis; fix time depends on the fault and parts, and DISCO-side faults must be fixed by the DISCO. Our 1-year service warranty applies under the applicable project terms. See how after-sales service works.
We can also check phase faults on systems installed by other companies, as a chargeable service, across Punjab.
Frequently asked questions
What does inverter phase loss error mean?
It means a three-phase inverter has found one or more grid phases missing or far outside limits, so it has disconnected. The cause is usually on the supply side: a DISCO fuse, a loose meter connection or a tripped breaker pole.
Why does my three phase inverter show one phase missing when I have electricity?
Because only part of your supply is on. Rooms on the two healthy phases still have power, but a three-phase inverter needs all three. Report the missing phase to your DISCO.
What is a phase sequence error on an inverter?
It means the three phases are connected in the wrong order for that inverter. It often appears after a meter change or rewiring. An engineer corrects it with a phase rotation meter; do not swap wires yourself.
What is a grid phase fault?
It is a general name some inverters use when one phase is missing, too high, too low or abnormal compared with the others. The screen or app usually shows the phase voltages, which help find the cause.
Is a phase loss error dangerous?
The inverter itself is protecting the system by stopping. The risk is to three-phase motors, which can overheat if they run on two phases. Switch them off until all phases return.
Is phase loss the same as phase imbalance?
No. Phase loss means a phase is missing or wrongly connected. Phase imbalance means all three are present but loaded or charged unevenly, which has different causes and fixes.
Sources
- Solis, "Solution to Inverter G-PHASE Alarm" (meaning, grid-side imbalance, wrong AC wiring sequence, cable and terminal causes)
- Huawei, SUN2000-(30KTL-A, 33KTL, 33KTL-E001, 40KTL) user manual, Troubleshooting (alarm 301 Abnormal Grid Voltage causes including phase imbalance and AC disconnection)
What you can check yourself
- Note the time and the areas or labelled circuits that lost power.
- Photograph the inverter warning and any phase readings shown on its normal screen.
- Check an existing utility outage notice, if available.
- Record whether the event affected nearby properties, without treating that as a confirmed diagnosis.
- Describe recent electrical work and whether power returned without intervention.
- Switch off equipment that is attempting to run abnormally using its normal controls, if safe. Do not keep trying to start a machine while its supply remains uncertain.
What not to do
- Do not bridge a missing phase from another phase, alter the neutral, bypass a changeover arrangement or probe live terminals.
- Do not disable grid protection so the inverter continues operating through a supply fault.
When to call us
- Report persistent or recurring phase warnings promptly. The installer can help establish whether the next action belongs with the utility, the building electrician or inverter service. If there is arcing, smoke or scorching, stay clear and seek urgent assistance.
Phase problems in Faisalabad and Lahore
Phase faults can start on the FESCO or LESCO side, in the building or at the inverter. Our Faisalabad and Lahore teams help work out which, so the right party fixes it.
Send us
The inverter model, complete warning, displayed phase readings, affected-circuit list, event timing, and your city and area.
Technical references
Reviewed 25 September 2026. Manufacturer documents are cited for general principles; your exact model’s manual always applies.