Symptoms: A circuit breaker trips while the measured load looks normal, sometimes at the same time of day.
Trip settings too low for the real load
Compare the breaker settings with the load study and the starting currents of the equipment it feeds.
Short load peaks such as motor starts
Record the current with a logger to catch the peaks a spot reading misses.
Trip unit or breaker ageing
Have the breaker and trip unit tested with secondary or primary injection.
Loose connection heating the breaker
Check the breaker terminals with thermography, since heat can make a thermal trip act early.
Prevention: Breaker settings recorded and tested on the protection maintenance schedule.
Breaker will not close
Hits OEE: Availability
Symptoms: The breaker does not close when commanded, or closes and opens again at once.
Closing spring not charged
Check the spring charge indicator and the charging motor and its supply.
Interlock still engaged
Check door, earth switch and key interlocks, which block closing by design.
Undervoltage release not energised
Check the control supply to the undervoltage release.
Closing coil or control circuit fault
Test the closing coil and its control wiring with the breaker isolated.
Prevention: Breakers operated and tested during planned maintenance so faults show up before they are needed.
Hot spots on busbars or terminals
Hits OEE: Availability
Symptoms: A thermal survey shows hot joints, discoloured busbars or a smell of hot insulation near a panel.
Loose bolted joints
Retighten joints to the specified torque during an outage under a permit to work.
Oxidised or corroded contact faces
Clean and remake the joint as the maker specifies.
Circuit carrying more than it was designed for
Measure the load and move or split circuits that are over their rating.
Worn contacts on a withdrawable breaker
Inspect the breaker contacts and the fixed contacts in the cubicle, and replace worn parts.
Prevention: Thermal survey of all switchboards under load once a year.
Signs of partial discharge or tracking
Hits OEE: Availability
Symptoms: A crackling sound, an ozone smell or tracking marks on insulators inside medium voltage switchgear.
Dirt and moisture on insulating surfaces
Have the panel cleaned and inspected during an outage. Only authorised electrical staff work on it, after isolation and earthing under your site electrical safety rules.
Anti-condensation heaters not working
Check that each panel heater and its thermostat work.
Cable termination fault
Have the terminations inspected and remade by a qualified cable jointer.
Damaged insulation
Have partial discharge measurements taken by a specialist to find the source.
Prevention: Partial discharge survey on medium voltage switchgear on a fixed interval.
Condensation and corrosion inside panels
Hits OEE: Availability
Symptoms: Water droplets, rust or white corrosion appear on metal parts and terminals inside the panels.
Panel heaters off or failed
Repair the heaters and check their thermostats are set correctly.
Cable entries not sealed
Seal cable entries and glands so damp air and water cannot get in.
Room temperature swinging day to night
Keep the switchroom at a steady temperature and close unused openings.
Wash-down or steam near the switchroom
Keep wash-down water and steam away from the room, and keep doors closed.
Prevention: Switchroom temperature and humidity checked, and heaters tested, before each cold season.
Earth fault trips
Hits OEE: Availability
Symptoms: Earth fault protection trips a feeder, sometimes only in wet weather or after cleaning.
Insulation breakdown on a feeder cable
Test the insulation resistance of the cable with it isolated.
Water in motor terminal boxes or junction boxes
Open and dry the boxes, replace damaged seals and check the glands.
Leakage current from drive filters
Check whether drives with filters on that feeder add up to more leakage than the setting allows.
Setting too sensitive for the circuit
Review the earth fault setting with a protection engineer.
Prevention: Insulation resistance of critical circuits tested and recorded on a schedule.
Protection relay alarm or self-test fault
Hits OEE: Availability
Symptoms: A protection relay shows an internal fault, a settings alarm or a current transformer alarm.
Relay hardware or self-test fault
Replace or repair the relay and re-test the protection before relying on it.
Current transformer wiring loose or open
Never open a current transformer secondary while primary current flows; have the wiring checked with the circuit isolated.
Settings lost or changed
Compare the relay settings with the approved settings record and restore them.
Auxiliary supply to the relay unstable
Check the battery or auxiliary supply that feeds the relays.
Prevention: Relay alarms reviewed weekly and protection tested on a fixed schedule.
Breaker mechanism slow or sticking
Hits OEE: Availability
Symptoms: A breaker is slow to open or close, or needs several attempts.
Old grease hardened in the mechanism
Have the mechanism cleaned and lubricated with the grease the maker specifies.
Breaker rarely operated
Operate breakers during planned maintenance so the mechanism does not stiffen.
Worn mechanism parts
Replace worn parts or the breaker if spares are no longer available.
Maintenance interval missed
Bring the breaker back onto the maintenance plan with its operating time tested.
Prevention: Breaker timing tests recorded at each maintenance.
Meters or indicator lamps reading wrong
Hits OEE: Quality
Symptoms: Panel meters show zero or impossible values, or position lamps disagree with the breaker state.
Voltage transformer fuse blown
Check and replace the voltage transformer fuses with the circuit made safe.
Control fuse or supply missing
Check the control supply to the panel indicators.
Meter or transducer fault
Test the meter against a calibrated instrument and replace it if it is out.
Auxiliary contact on the breaker misaligned
Check the auxiliary contacts that drive the position lamps.
Prevention: Panel readings compared with a portable meter once a year.
Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.
Recurring switchgear stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.