Arkansas HVACR NewsMagazine November 2022

HVACR NewsMagazine November 2022

Tech News

Why is the Breaker Tripping?

Inappropriate Circuit Design

Improper circuit design can result in an overload condition when the circuit ampacity (amperage capacity) or the circuit breaker size is not correctly matched to the load. That can happen because the load matching was wrong in the first place. In other cases, someone might have added additional load to the circuit later on. For HVAC equipment, the conductor size should be matched to MCA (minimum circuit ampacity). The circuit breaker or fuse should be matched to the MOCP (maximum overcurrent protection). If the conductor is smaller than the MCA rating, or the breaker is lower than the MOCP rating, it can result in a tripping breaker. You will also see cases where more than one system will be connected to one circuit breaker. That's incorrect unless the systems have additional independent overcurrent protection. These issues usually cause an intermittent trip, as it takes time under load to show up. But of course, that all depends on the severity of the problem. Overload An overload condition occurs when the loads draw more current or do more work than they are designed for. Common overload conditions would be a compressor locking up, motor bearings binding, blower belts too tight, or sheaves adjusted improperly. And overload generally occurs with inductive (magnetic) loads like motors. In several cases, the motor is either placed under a greater torque load than it's designed for or is beginning to fail mechanically.

Breakers are designed to trip anytime the circuit draws a current above the rating for a period of time. The time the breaker takes to trip is a function of how high the circuit amperage is compared to the breaker rating. The higher the amperage above the rating, the faster the breaker will trip. Breakers can accomplish that thermally by tripping on increased temperature. They can also do it inductively by tripping on the increased magnetic field when amperage increases. Most residential circuit breakers are thermal, which means they are more prone to trip during high ambient temperature than during low ambient temperature. That's one factor that explains why you will receive more nuisance or intermittent breaker tripping calls on a hot summer day. Many times, breakers get replaced just for doing their job and tripping when they should. There are five common causes of breaker tripping: improper circuit design, overload, ground fault, leg-to-leg short, and breaker issues.