MCC Maintenance and Inspection for GTA Plants and Buildings

What MCC Maintenance Covers in a Motor Control Centre

MCC maintenance is the inspection, cleaning, tightening and testing of a motor control centre's bus, plug-in units and the starters, overloads, disconnects and controls inside them. MCC inspection is the part done live, mainly visual and infrared, to decide what needs attention at the next outage.

A motor control centre, or MCC, gathers the controls for many motors into one lineup of vertical sections. A horizontal bus runs across the top or middle, vertical bus in each section feeds the plug-in units, often called buckets, and each bucket typically holds a disconnect or molded-case breaker, a contactor, an overload relay and a control transformer. Many modern lineups add variable frequency drives, soft starters, PLC input and output wiring and network communications.

Lineups also change over their life far more than switchgear does. Buckets are swapped when motors are replaced, drives are added to old sections, spare spaces are filled and control wiring is modified during line changes. Each change is a chance for a wrong overload setting, an unlabelled circuit or a missing barrier, so part of every visit is confirming that the lineup still matches its drawings and bucket schedule.

Because an MCC feeds the equipment that actually makes product or moves air and water, a failure there stops a line rather than a light fixture. It also concentrates risk: dozens of connections, stab contacts and moving parts sit in a single enclosure, and a fault in one bucket can involve the bus that feeds them all. Maintenance keeps each of those small parts from becoming the weak point.

MCC Inspection Checklist: Bus, Buckets, Starters and Controls

Our MCC inspection checklist follows the power path from the incoming lugs to each motor lead, then covers the controls and enclosure. Every item is recorded as found, corrected or recommended.

• Incoming section and main bus: lugs and terminations, bus joints, bus supports and insulators, signs of heat, tracking or arcing.
• Vertical bus and stabs: stab fingers and their springs, bus barriers and shutters, evidence of pitting or discolouration where buckets plug in.
• Buckets and units: door interlocks, operating handles, breaker or fused disconnect condition, wiring, terminal tightness and labelling.
• Starters and contactors: contact wear, coil condition, arc chutes, mechanical freedom and auxiliary contacts.
• Overload relays: settings compared with the motor nameplate full-load current and service factor, and trip function where testing is in scope.
• Drives and soft starters: cooling fans, filters, heat sinks, fault logs and enclosure ventilation.
• Control circuits: control transformers, fuses, pilot devices, interposing relays and the wiring that ties them to the process control system.
• Enclosure and room: missing filler plates or covers, open conduit knockouts, dust, moisture, ambient temperature and clear working space.

How Often Should a Motor Control Centre Be Maintained?

Most MCCs should be scanned and walked yearly and fully serviced every one to five years, and the plant environment usually decides where in that range a lineup falls. NFPA 70B covers motor control equipment in Chapter 28 and sets the interval through its equipment condition assessment, while ANSI/NETA MTS (2023 edition) defines the tests done at each service.

Under the 2023 edition's Table 9.2.2, motor control equipment carries one interval for all tasks, and infrared thermography has its own:

The examples in the first column are our illustration of how the three factors usually combine; the actual rating comes from assessing your lineup, and the worst of physical condition, criticality and environment wins. Manufacturer instructions take priority where stricter. In food and beverage plants, washdown and humidity often push MCCs into the shortest interval, while the same lineup in a clean warehouse electrical room may justify the longest. Our electrical preventive maintenance programs schedule MCCs alongside the switchgear that feeds them.

Lockout on Motor Control Equipment Under Ontario Rules

MCC work in Ontario is done under section 42 of Regulation 851, which requires the supply to be disconnected, locked out and tagged before work on or near exposed live parts, and it demands particular care because buckets and controls can be fed from more than one source.

The provincial ministry has issued a hazard alert on electrical lockout using manual motor controllers, pointing employers to subsections 42(1), (2) and (7): disconnect, lock and tag; have each worker confirm it; and keep written procedures. In an MCC that means isolating at a proper disconnecting means, not at a start-stop station or a motor controller that only interrupts the control circuit.

Other MCC-specific hazards we plan for:

• Control power fed from a separate panel or a PLC rack, which stays live when the bucket disconnect is open.
• Drives and capacitors that hold stored energy after isolation and need time to discharge.
• Racking or withdrawing buckets from an energized bus, which is done only under CSA Z462 controls with the correct PPE.
• Back-feed from other sources, such as interlocked tie feeders or generator connections.

Before work starts, our crew lead walks the lineup with your maintenance contact, confirms the disconnecting point and every secondary source for each bucket on the list, and records them on the work permit so the next shift can see what is isolated and why.

Section 41 also requires a conspicuous warning sign on any room with exposed live parts, which we check on every visit. Where incident energy labels are missing on the lineup, we recommend an arc flash study before any energized work.

Testing Starters, Overloads and the Motors They Feed

A full MCC service tests the protection in each bucket and, where you ask for it, the motor circuit beyond it, because a healthy starter feeding a failing motor is still a failure waiting to happen.

• Insulation resistance on the bus, the outgoing cables and, with the motor leads included, the motor windings, recorded so the trend can be followed year to year.
• Overload relay testing to confirm the relay trips within its class at the current set for the motor, and that the setting matches the nameplate.
• Molded-case breaker checks inside each bucket, using the methods set out under circuit breaker testing.
• Contactor checks for contact wear and coil pickup and dropout, and functional tests of start, stop, interlock and permissive circuits with operations staff present.
• Connection torque on bus joints, lugs and terminals to the manufacturer's values.

Readings are judged against the motor control acceptance values in ANSI/NETA MTS and the manufacturer's data. Motors that show low insulation or unbalanced readings are followed up with deeper diagnostics through our motor electrical testing service.

Servicing an MCC Without Stopping the Whole Plant

We plan MCC work so that only the motors being serviced are down. Buckets can often be serviced one at a time with only their own load isolated, while bus and full-section work is grouped into a scheduled shutdown.

During scoping we sit with your maintenance lead and production planner to map each bucket to the equipment it runs and how long that equipment can be down. That produces three lists: buckets that can be isolated at any time, buckets that must wait for a line changeover or weekend, and work that needs the whole MCC dead, such as bus joint torque and full insulation testing. Infrared scanning is done first with everything running, so the shutdown time goes to the problems the scan found.

For plants in Brampton, Vaughan and Kitchener-Waterloo and Cambridge, that often means early-morning starts before the first shift or work over a planned maintenance weekend. IHSA's COR on our file and our prequalified listings on ISNetworld, Avetta and ComplyWorks, shorten the paperwork for sites that vet every contractor.

Common MCC Problems We Find and Fix

The faults we find most in motor control centres are heat at stab and lug connections, dust and moisture inside the lineup, overloads set wrong, and safety features that have been bypassed. Most are cheap to fix once found and expensive to ignore.

• Hot stabs and lugs: loose or worn stab fingers and terminations that show up as hot spots on a thermal scan, often long before any trip.
• Contamination: conductive dust from mills and packaging lines, flour and sugar dust in food plants, and condensation where washdown areas meet electrical rooms.
• Wrong overload settings: overloads left at a previous motor's value after a motor swap, or set high to stop nuisance trips.
• Defeated interlocks: door interlocks bypassed so a bucket can be opened while live, which removes a key safety barrier.
• Open spaces: missing filler plates, blank covers or knockout seals that let in dust and leave live parts reachable.
• Drive cooling: clogged filters and failed fans on drives in MCC sections, which shorten drive life and cause heat trips.

Our electricians carry the tools and common parts to correct most of these during the visit with your approval, and our Level II certified thermographers can rescan afterward to confirm the fix. For hot spots across the wider plant, see industrial plant thermography.

Your MCC Report and Who Needs MCC Maintenance

After each visit you receive an MCC report listing every section and bucket, what was found, what was corrected and what is recommended, with test values and photographs. Any facility whose production, water, air or heat depends on a motor control centre benefits from that record.

The report includes a bucket schedule with the load served, breaker or fuse rating, starter size and overload setting against the motor nameplate; as-found and as-left condition; insulation and overload test results; thermal images of any hot connections; and ranked recommendations. Condition labels are applied to the lineup after maintenance so operators can see its status.

Our MCC clients include manufacturing plants, food processors, warehouses and distribution centres with conveyor and sortation lines, and commercial buildings whose chillers, pumps and air handlers run from MCCs. A small lineup in a clean room with few critical loads can safely run on the longest interval with a yearly scan. When an MCC fails between visits, maintenance-contract clients have emergency response, and repair work is notified to ESA under our licence, ESA/ECRA #7014042.