MCC Retrofit vs. Replacement: How to Choose

Once you know your motor control center needs attention, the next question is harder: do you keep the existing structure and upgrade what's inside it, or pull the whole lineup and start over? If you're still deciding whether an upgrade is needed at all, our industrial electrical blog has a full post on the warning signs that it's time to upgrade an MCC. This guide is for the step after that, when the answer is yes and you need to pick a path.

There's no single right answer. A retrofit can save months and a lot of money when the structure is sound. A full replacement can be the cheaper choice over ten years when the bus, the ratings or the parts supply are working against you. The trick is checking the right things before anyone orders equipment.

The Three Ways to Upgrade an MCC

Most MCC upgrades fall into one of three paths.

1. Bucket-for-bucket retrofit (retrofill). The vertical sections and bus stay in place, and old units are swapped for new or reconditioned plug-in units built to fit that structure. Several manufacturers offer direct replacement units for legacy lineups, including some built for other brands' structures, constructed to the same UL 845 standard as a new MCC. This is the least disruptive option because units can often be changed one at a time during short outages.

2. Partial rebuild. Some sections are replaced or new vertical sections are added to the existing lineup, usually to make room for drives, add capacity or replace the worst sections first. This works when the existing bus can be extended and the new sections are compatible with the old ones.

3. Full lineup replacement. The entire MCC comes out and a new one goes in. This is the biggest project and needs a planned shutdown, but it resets the ratings, the parts supply and the safety features all at once.

Start With the Structure, Not the Buckets

The buckets get the attention because that's where starters fail and where operators see problems. But the decision usually comes down to the parts you don't swap: the bus, the enclosure and the ratings.

Bus condition. Look for discoloration at bus joints and stab connections, signs of past overheating, loose hardware and contamination. An infrared scan under load and an insulation resistance test on the bus tell you a lot more than a visual check. Our guide to insulation resistance testing and what Megger readings reveal explains how to read those results. If the bus is in poor shape, putting new units on it doesn't fix the real problem.

Short-circuit rating vs. available fault current. Every MCC has a short-circuit rating based on how its bus is braced and how its units were tested. NEC 430.98(A) requires an MCC to be marked with its common power bus current rating and its short-circuit rating, and NEC 430.99 requires the available fault current at the MCC, and the date it was calculated, to be documented. The problem with older lineups is that the available fault current often goes up over the years. A larger utility transformer, a new service or added generation can push it past what an old MCC was built to handle. Equipment applied above its rating is a code violation under NEC 110.10 and a real hazard during a fault. If the numbers don't work, a retrofit can't fix it, because the bus bracing is part of the structure. The same idea applies to control panels, which we covered in SCCR on industrial control panels and what NEC 409 requires.

Enclosure and environment. Rust, damaged doors, missing barriers and corrosion inside the structure all count against a retrofit. If the room is wet, dusty or corrosive, check whether the enclosure type still suits the space. Our post on corrosion in industrial electrical systems covers what to look for.

The UL 845 Question

MCCs are listed under UL 845, and that listing covers how the structure and its units were built and tested together. This matters more than many people expect.

Replacing a unit with one that is listed for that structure, from the original manufacturer or a supplier that builds and certifies units for it, keeps you on solid ground. Building your own units, modifying the contents of an existing bucket, or mixing in units that weren't tested with that structure can put the listing of that unit, and possibly the whole lineup, in question. That can create problems with inspectors, insurers and manufacturer support.

Before a retrofit, confirm that listed replacement units are actually available for your exact lineup and vintage. For some older or orphaned brands, the choices are limited to a short supply of reconditioned units. That's fine as a stopgap, but it isn't a long-term plan.

When Adding Drives Changes the Math

Many MCC upgrades happen because a plant wants to add variable frequency drives. That's a good reason, but drives change things.

• Space. A VFD unit is usually taller than the starter it replaces, so a full section can run out of room quickly.
• Heat. Drives give off heat inside the enclosure. Older sections weren't designed for that load, and ventilation or the room's cooling may need to change.
• Motor protection. Long cable runs from MCC-mounted drives to motors can cause reflected wave problems at the motor. Our post on why motors fail on VFDs explains the causes and the fixes.

New motors matter too. If the upgrade comes with motor replacements, check how the new motors will affect starters and protection. Our post on the 2027 DOE motor efficiency rule covers what's changing for plants.

Safety Features You Only Get With New Equipment

A retrofit improves the units, but the safety design of the structure stays the same. Some features only come with a new lineup:

• Arc-resistant construction. Some low voltage MCCs are now built and tested to IEEE C37.20.7 to contain and redirect the energy of an internal arcing fault away from personnel.
• Better isolation. Newer designs can include shutters that cover the vertical bus when a unit is withdrawn and other barriers that reduce exposure during maintenance.
• Smarter units. Networked overload relays and drives let your controls system see motor current, trip causes and run hours without opening a door.

If your facility is trying to reduce arc flash exposure, these features can carry a lot of weight in the decision.

Retrofit or Replace: A Quick Comparison

If most of your answers land in the right column, a full replacement is usually the better investment, even if the upfront cost is higher.

Planning the Work Around Downtime

A retrofit can often be done in stages, one unit or section at a time, during weekend or shift-change outages. A full replacement needs a defined shutdown window, a plan for temporary power if any loads must stay running, and equipment ordered well ahead, since new MCC lead times can be long.

Plant shutdowns are often the best time for this work. Our guide to holiday shutdown electrical maintenance covers how to plan scope, parts and crews so the window doesn't slip.

What to Update After Any MCC Upgrade

Whichever path you choose, the job isn't done when the last unit is energized.

• Markings and fault current documentation. Confirm the MCC marking reflects the bus rating and short-circuit rating, and update the documented available fault current per NEC 430.99.
• Arc flash risk assessment and labels. NFPA 70E requires the arc flash risk assessment to be updated when a major modification takes place and reviewed at intervals not exceeding five years. New units, new protective devices or a new lineup can change incident energy, so labels may need to change too.
• Drawings and schedules. Update one-lines, unit schedules and control drawings so the next person working on the MCC sees what's actually there.
• Testing and startup. Insulation resistance tests, torque checks, protective device settings and functional checks on each unit before turning it over to production.
• Maintenance program. Add the upgraded MCC to your electrical maintenance program with a baseline infrared scan and test results to compare against later.

How HRE Can Help

HRE Construction works with industrial facilities to evaluate, upgrade and replace motor control centers with as little disruption to production as possible. Our team can help you:

• Assess bus condition, enclosure condition and test results on your existing MCC
• Compare the MCC's short-circuit rating with the available fault current at its location
• Confirm whether listed replacement units are available for your lineup
• Plan retrofits in stages or a full replacement around your shutdown schedule
• Install, test and start up new units, drives and lineups
• Update markings, drawings and documentation after the work is done

Whether you need a few buckets replaced or a new lineup, HRE Construction can help you make the call with real data from your facility.

Frequently Asked Questions

Is it cheaper to retrofit an MCC or replace it?

A retrofit usually costs less up front and causes less downtime. But if the bus is in poor condition, the short-circuit rating is too low or replacement units are hard to find, a full replacement often costs less over the life of the equipment.

Can I put a different brand's bucket in my existing MCC?

Only if the unit is built and listed for your specific structure. Some suppliers make listed replacement units for other manufacturers' lineups. Units that weren't tested with your structure can put the UL 845 listing in question, so confirm before you buy.

How do I know if my MCC's short-circuit rating is still adequate?

Compare the rating marked on the MCC with the current available fault current at its location. NEC 430.99 requires that available fault current and the date of the calculation to be documented. If the system has changed since the last calculation, have it recalculated.

Do I need a new arc flash study after an MCC upgrade?

NFPA 70E requires the arc flash risk assessment to be updated after a major modification. Even a partial upgrade can change protective devices and incident energy, so the assessment should be reviewed and labels updated where they're no longer accurate.

Ready to Plan Your MCC Upgrade?

If your motor control center is due for an upgrade, the right first step is a clear look at what you have. Contact our team or request a quote and we'll help you decide whether a retrofit or a replacement makes the most sense for your facility.