Why does a three-phase inverter show overload when total load looks low?

What you will see

• Backup trips when a particular AC, pump or machine starts.
• The total displayed load appears below the inverter’s advertised rating.
• One phase carries much more load than the others.
• Trips began after appliances or circuits were added.

Why it happens

A three-phase inverter has an overall output rating and limits for individual phases. Supported imbalance varies by model. Spare capacity on one phase does not automatically make the same capacity available on another; the manufacturer’s per-phase specification must be checked.

Starting current is a separate issue. A motor or pump can briefly demand much more current as it starts, potentially exceeding an inverter’s permitted limit even though its running load seems acceptable.

This is why the circuit allocation matters. Several demanding single-phase appliances may be concentrated on the same phase. The installer needs to compare the actual allocation with the equipment’s limits and the loads that operate together.

An “overload” description should also be checked against the exact warning. A battery restriction, a grid fault and an inverter output overload are different events; a low total-power screenshot cannot identify which one occurred.

Diagram

Low total, one phase over

Total view

Total rating

Total load

Looks well within the rating.

Per-phase view

Per-phase limit

L1L2L3

L1 is over its own limit.

A motor or pump start can briefly exceed the limit even when its running load looks fine.

What you can check yourself

• Save the full alarm text and event time.
• Capture each phase’s power or current from the normal monitoring screen, where available.
• List the appliances starting or running when the trip occurred.
• Record whether the problem happens on grid supply, battery backup or both.
• Check the existing circuit schedule or handover diagram for the affected appliances.
• If circuits are not labelled by phase, say so. Identifying them is part of the electrician’s assessment; customers do not need to open the board or move cables.

What not to do

• Do not bridge phases, move circuits yourself, increase protection settings or repeatedly restart the appliance to reproduce a trip.
• Do not apply a universal “one third per phase” rule without checking the inverter specification.

When to call us

• Arrange a load review if one appliance repeatedly trips backup, phase readings are heavily uneven, or the problem started after new equipment was connected. The review should cover starting demand, phase allocation and the exact backup rating.

Load reviews in Faisalabad and Lahore

Three-phase homes, shops and mills across Faisalabad, Lahore and Punjab often add single-phase ACs over time. Our team reviews the phase allocation against your inverter’s limits.

Send us

The inverter model, battery arrangement, phase screenshots, appliance list, alarm details, and your city and area.