The air circuit breaker (ACB) on your main LT panel is the one device that stands between a fault and a plant-wide shutdown. It is also the device most often left untouched for years. This guide explains what an ACB maintenance visit should include, how often it is needed, and the warning signs that your breaker needs attention now.
Why ACBs need regular service
An ACB is a mechanical device. Its springs, latches and contacts must work in a fraction of a second, often after sitting closed for months. Dust, heat, dried grease and contact wear slow it down. A breaker that does not trip on time turns a small fault into a fire or a burnt panel.
What a proper ACB service includes
- Visual inspection of the breaker, arc chutes, and cradle for burning, cracks or tracking marks.
- Cleaning and lubrication of the operating mechanism with the grease the manufacturer specifies.
- Contact check: wear of the main and arcing contacts, and contact resistance measured with a micro-ohm meter.
- Insulation resistance between poles and from each pole to earth.
- Mechanism operation: close, open and trip operations, spring charging, and the closing and shunt trip coils.
- Trip unit testing by secondary injection, to confirm the overload, short-circuit and earth fault settings actually trip the breaker within the set time.
- Racking and interlocks in the cradle checked for smooth operation.
- Written report with readings and settings, so the next service has a baseline.
How often should an ACB be serviced?
For most plants, a full service once a year is a sensible minimum. Breakers in dusty, hot or humid locations, or those that have cleared a heavy fault, need it sooner. Always follow the manufacturer’s maintenance schedule where one exists.
Warning signs your ACB needs attention now
- The breaker trips without a clear reason, or fails to close
- Spring charging is slow or the motor runs for too long
- Burning smell, discolouration or hot spots seen on thermography
- The trip unit shows a fault or its display is dead
- The last service record is missing or more than a year old
Service or replace?
Many older ACBs can be brought back with a proper overhaul. Where spare parts are no longer available, or the trip unit cannot be tested, a retrofit with a current breaker in the existing panel is often cheaper than a new panel and needs a shorter shutdown.
ACB service in Lucknow and across UP
Tajalli Tech provides ACB maintenance, service and testing for all major makes, including trip unit testing by secondary injection. We are a Schneider Electric EcoXpert partner for low-voltage services. Our teams cover ACB services in Lucknow and Kanpur, along with other cities in Uttar Pradesh. Call 0522-4956473 or send an enquiry with the breaker make, rating and number of units.
Questions
How long does an ACB service take?
Usually a few hours per breaker, including testing. The breaker must be isolated, so plan it with a shutdown.
Can an ACB be serviced without a shutdown?
The breaker itself must be de-energised and racked out. In panels with more than one incomer, the load can sometimes be shifted so that only part of the plant is affected.
What is secondary injection testing?
It is a test where a current is injected into the trip unit to check that the breaker trips at the set current and time, without passing full fault current through the breaker.
Do you service all ACB makes?
Yes, we service ACBs of all major makes, and handle retrofits where an old breaker can no longer be supported.