Learn about the various types of MCC and get practical tips for choosing the right one.

Key Takeaways:

  • MCCs are either manually operated, semi-automatic, or fully automatic
  • MCC iterations include fixed, plug-in, and withdrawable
  • The right choice of MCC type depends on application complexity, cost, and ease of operation

Every kind of motor control center (MCC) has many sensitive moving parts working together to keep vital business functions like air conditioning, heating, and factory production processes running. These complex cabinets contain motors, fans, circuit breakers, and fuses and can be confusing for anybody who isn’t an electrical professional.

Things can get really perplexing when you start looking at the various MCC designs available. Don’t worry – we’ve created a breakdown of the most common iterations and how they stack up against each other in different scenarios. Here’s your handy side-by-side comparison of some different MCCs and which criteria will help your business choose the right model for its needs.

MCC design basics

MCCs are vertical cabinets containing the motor starter units for various business functions, all contained in a central location for ease of access. MCC voltages vary. In some cases, low voltage designs can manage voltages ranging from 230 V to under 1000 V while in others, this is capped at 600V. Medium voltage designs sometimes cap at 7.2 kV (7,200 V) but may extend to 15,000 V and above.

MCCs can be fully automatic, semi-automatic, or manually controlled. Fully automatic kinds have the most internal sensors and use a control circuit to adjust motor speeds independently and self-diagnose problems for operators to address.

Semi-automatics also use sensors but will require human input to perform some functions. With manual MCCs, it’s entirely up to people to make the motor adjustments and look for problems. This might seem the low-tech, undesirable option, but manual operation can be valuable in an emergency where MCC’s have failed and need to be stopped quickly.

Fixed vs plug-in MCC

The three main MCC types are fixed, plug-in, and withdrawable. Let’s compare the first two since they’re the most structurally similar. Fixed type MCCs have components like outgoing cables, contactors, and molded case circuit breakers (MCCBs) fixed into position within the MCC’s cabinet frame. This all-in-one kind of assembly is good and bad.

Good, because everything electricians and operators need to work with is centralized. The compartments are also arranged to provide adequate operating space between motor starters and operators. Bad, because to carry out work on any one part, it’s usually necessary to shut the entire MCC down before opening the main incomer to avoid electrocution and isolate the problem. 

Plug-in types offer more versatility than fixed MCCs because they allow some motor controllers to be plugged into and out of the main MCC frame, which helps with maintenance and performance tests. The comparison isn’t really between fixed and plug-in MCCs if you want to see significant differences. It’s between fixed designs and withdrawable, with the latter providing clear advantages.

Why withdrawable MCC features are so beneficial

Also called “fully draw out,” this type of MCC is extremely convenient for both electrical professionals and the businesses themselves. Unlike fixed MCCs where components are integrated into the frame, the various module components in withdrawable MCCs can be slid in and out separately on telescopic rails. 

This makes it much easier to find and fix a problem with a particular part. Sometimes this is an obvious repair while at others isolated testing or upgrading of certain components may be necessary, all of which are streamlined by withdrawable features.

The second big advantage of this more modular design is that the whole MCC doesn’t need to be shut down while electrical work takes place; only the section in question needs to be disconnected. This allows other business functions connected to the MCC to keep running while faulty ones are offline.

Withdrawable MCC sections also remove the risk of electric shock during inspection and maintenance, while increasing the speed of inspections, tests, upgrades, and repairs. These benefits help to keep people safe and cost businesses less money for electrical services, while minimizing even more costly operational downtime.

A step down from fully draw out designs is the semi-draw out. These typically only allow the voltage source to be separated from the rest of the MCC, however this still makes it simpler, safer, and faster for electricians to work on this component.

How to choose the right MCC for your business

Simply looking at the three-way comparison above and considering the pros and cons won’t be enough for businesses to make a final decision on which type of MCC to install. Here’s a checklist of the other main deciding factors:

  • Your site’s power supply
    Whether your building runs on AC (Alternating Current) or DC (Direct Current) will affect voltage considerations for your MCC. This relates to ampacity concerns, which is the most current an MCCs horizontal bus can safely manage.
  • Your site’s layout
    Your motor control center must be, well, central! The optimal position for your cabinet(s) may not be a matter of choice but dictated by your business’ dimensions. This in turn could influence the size of your MCC and the layout of its cabling (overhead or underground). Another consideration is if you plan on expanding your business operations which will require adding more MCC cabinets in the future and necessitate more space.
  • Environmental factors
    MCC rooms must be well-ventilated and strictly temperature controlled. Wherever they’re installed, the management of fine particulate matter, moisture, and humidity must be a top priority. MCCs in various environments (especially in industrial ones) require different levels of ingress protection, which again could influence the model you select.

 Lastly of course, there’s the cost element. Make sure your business speaks to a reputable and experienced electrical contractor who’ll listen to your needs, assess your premises, and give you a transparent quote so you can budget more effectively.

Contact UES for expert electrical advice

We’re here to provide decades of electrical insight for South Florida industries of many different kinds. Just contact us with any motor control center questions, or to get a free quote on our many electrical services!