Heating, ventilation, and air conditioning (HVAC) systems play an essential part in our homes as well as commercial and industrial buildings. While addressable attention is given to compressors, motors, and control units, the importance of electrical protection is frequently ignored. In fact, the use of the correct fuse can be central to protecting HVAC systems against electrical fault, nuisance downtime, and potentially costly damage to the equipment itself.
In this article, we review why fuses are important in HVAC applications, how to choose the right type, and what engineers and system integrators should look out for when designing suitable electrical protection.
Why Electrical Protection Is Important in HVAC Systems
HVAC systems are at risk from variable electrical loads. Compressors, blowers, inverters, control boards and more in turn experience a series of starts and stops alongside surges in current and frequent variations in voltage. One or more of these conditions can lead to:
Winding damage in electrical motors
Failure of power electronics
Heated wires and connectors
Shutdowns, or even fires
Fuses offer a simple but very effective response. If there is abnormal current flow, a fuse cuts that flow before the risk of damage expands and worsens to involve other vulnerable components. In conjunction, the replacement of a fuse is by far the quickest and cheapest option compared to the need to repair or replace HVAC equipment.
Common Electrical Faults Typically Encountered in HVAC Applications
A grasp of typical faults leads to an appropriate understanding of correct fuse rating and characteristics. One notable condition is of an over-current nature, which occurs in compressor startup as well as when a mechanical overload halts operation in its tracks. Numerous other electrical faults include:
Short circuit due to failure in insulation, water ingress, wiring glitches
Ground faults arising in poorly maintained systems or ageing units.A fuse fast enough to prevent component failure, but slow enough not to nuisance trip in the specific application is required. All the above require fast-acting fuses.
Fuse Types Used in HVAC
Auxiliary heating circuits, roof-top units, and packaged HVAC systems all will utilize different fuses. There are few single solutions.
Time delay (sloblow) fuses—commonly used in motors and compressors for allowing inrush current without nuisance tripping, a steady overcurrent flow will trip the element for protection.
Fast-acting fuses—typically faster acting for short circuit use, new applications include Power Cables Plugging.
High voltage fuses—used in commercial units typically protect transformers and main feeders, applied in the power distribution sections.
Semiconductor fuses—much new HVAC technology is based on variable frequency drives and power inverters with IGBTs and MOSFETs included. Fast declining fault current requires protection devices to protect all facets of the electrical circuit with fuses rapidly becoming avant-garde.
Fuse and Circuit Breaker in HVAC Protection
Fuses and circuit breakers both have advantages. The fuse has many attributes.
Faster response to fault
Higher current-limiting abilities
Simple and reliable
Today, the circuit breaker affords reset
Allows anticipation of errors
Easier to maintain access
Most circuits are laid out to use upstream devices separate from circuit breakers in the HVAC system that primarily control operations and tripping.
Choosing the Right Fuse for HVAC Systems
Just to get a good fuse the first time comes from trials on the operating current versus fault current. Considerations:
Rated current and voltage to match system, with slightly more current than the normal operating parameter.
Breaking capacity must break the maximum potential fault without failure.
Time-current characteristics, matching the startup with the actual fuse characteristics. High speed units are designed for use with motors matched. Trouble is, get a high-tech fuse and something in that panel is called out.
Environmental conditions with outdoor installations that might move the humidity right from the ground and splash about may seek higher fusing.
Inequalities with torsion in leads and cutouts may dictate a higher replacement.
Demand of Power Electronics
HVAC systems designed around aesthetics and high technology electricity monitoring via computers and Gaussian logic. We see this particularly in compressor motors (and drives) primarily. The existence of the equivalent of voltage dump circuit demand of other components.
Need a fast isolation of fault to protect fuses installed. Luckily, ready made high quality electrical protection helps boost system reliability for a better uptime too.
Long Term Gains
Proper protection has its gains from just plain turning the HVAC unit on and being able to sleep knowing it is properly safeguarded to its maximum potential.
Less calling in to pay out
Less shutting down and placarding to sweep and blow out fuses and cicuits from making numerous unions.
Of course fault severity increases randomness and potential of gridlock from waiting hours on maintenance.
Conclusion
All fuses must do their part for perfection long before the technicians hand and eyes an injury or assembly of big name emergency electrician down from the Coast!
