Fuses vs Circuit Breakers in Industrial Control Enclosure Design: A Panel Designer’s Perspective

The Fundamental Questions to Ask at the Start of an Industrial Control Enclosure Design

It’s one of the first questions asked when beginning an industrial control enclosure design. Are we using circuit breakers or fuses to protect our equipment? How does one choose what to specify? What are the pros and cons of either choice?

How do you choose what to specify?

At Concept Systems, fuses are normally used when trying to achieve higher short circuit current ratings (SCCR). I’m defining “higher�? SCCR ratings as over 10kA (10,000 amps). If the design can handle a lower SCCR rating, then circuit breakers definitely come into play. There are ways to get circuit breakers to work above that threshold, but as you will see, it can be trickier to coordinate components to achieve the desired SCCR goal.

The advantage of circuit breakers is their ability to reset. So, we typically use circuit breakers as branch circuit protection, and control circuit overcurrent protection on most 120vac loads mainly because of their convenience.

We also use them in that location because they easily exist under transformers where the available fault current (AFC) is much less than the 480V AFC. Since circuit breakers tend to be more convenient from an operations perspective, their preferable, however as the needed SCCR rises, their suitability from a specifications standpoint becomes more questionable.

What are the pros and cons?



  • Easy to raise the SCCR of an industrial control enclosure
  • Most power equipment has been evaluated with fuses to include high SCCR ratings
  • Many power distribution blocks have been evaluated with fuses to include high SCCR ratings. I mention these specifically because I’ve found that this is the weak link in many possible solutions with circuit breakers.


  • Larger than most comparable circuit breakers so they take up more panel space. The difference becomes more pronounced as the amperage rating increases. This is especially the case when combining them with disconnect switches.
  • You have one shot. If you blow the fuse, you need to have another one around or you’re shut down until you get a new fuse.

Circuit Breakers


  • Multiple chances to clear a fault. If you trip the circuit breaker, you may have another shot at fixing the problem, and trying again.
  • Size. Circuit breakers tend to be smaller than fuse / fuse holder combinations especially when disconnecting is required, and at larger amperages.


  • Not coordinated with as much equipment, so achieving higher SCCR values can be tricky.
  • Most power distribution blocks are not rated for classes of circuit breakers, but a few are rated for specific ones. If you can find that magical combo of circuit breaker and power distribution block, or if you don’t need power distribution blocks, you have a shot at using circuit breakers to achieve high SCCR ratings.

Why high SCCR’s and circuit breakers don’t mix well

As I eluded to earlier in the article, really a major hurdle in using circuit breakers in a design with high SCCR needs is the power distribution blocks. If you need to distribute to multiple loads these can be a necessity. The trouble with them is that UL 508A only allows power distribution blocks to have a 10kA standard SCCR rating. To be able to apply a larger SCCR rating to the block, you’d need to coordinate it with a tested device.

Since fuses can be classified by standard well defined trip classes, a supplier can test their power distribution block with a particular class of fuse, and then all of a sudden, all of the fuses in that class become usable in raising the SCCR rating of the block. In contrast, power distribution blocks to date have not been linked to circuit breaker trip classes, but instead are linked to specific part numbers.

This means that if the circuit breaker you want to use hasn’t been tested and approved for use with the block you get no high fault SCCR bonus. In that instance, 10kA is the SCCR value of the block as used in that circuit, and likely the best SCCR rating you can give your enclosure without a lot more head scratching.

As an example, please see this link to a specifications page for a power distribution block, and look at the table on page 3. Notice how the SCCR with fuse protection is based on the class of fuse protection with a max limit on the amperage of fuse used the only limitation. Now look for a similar chart associated with circuit breaker options. You will notice how there are no circuit breaker options to raise the SCCR rating. If you need a higher SCCR rating, the easiest, and maybe even the only solution is fuses.

I’ve focused a lot on the power distribution blocks and circuit breakers. The problem is similar with circuit breakers and devices, like drives or motor starting equipment, in that the devices need to be tested together. However there is an important advantage for downstream equipment, and that is where the device appears in the power system.

Power distribution blocks typically appear in the feeder portion of the system which has fewer options for modifying the SCCR value of the block, and therefore makes them a difficult obstacle.

AFC vs SCCR in layman’s terms.

Available Fault Current (AFC) = How much short circuit current can be delivered in a worst-case short circuit scenario.

Short Circuit Current Rating (SCCR) = How much fault current the equipment can withstand as the result of an internal or downstream short circuit without something in the cabinet exploding in a ball of fire.

If the AFC of the system is greater than the SCCR of the equipment and a short circuit happens you may get a fireball. If the AFC is less than the SCCR of the equipment in theory you should not get a fire ball, but you might get some magic smoke.

Take away: The ability to correctly calculate the SCCR of an industrial control enclosure is important to the safety of your system, and facility. If you need help with reviewing your system design, contact Concept Systems to see what it would take to get an expert review of your design.

Industrial Enclosure Design with Concept Systems

Learn more about Concept System’s work in control panel design here.