Arkansas HVACR NewsMagazine November 2022

HVACR NewsMagazine November 2022

Tech News

Overload conditions often don't trip a breaker because the motor itself will usually have an overload that specifically protects the motor. That is why a locked compressor is much more likely to shut off on thermal overload than it is to trip a breaker, even though it will draw far higher amps than the breaker rating on startup. In these cases, the thermal overload is designed to respond quicker than the breaker. If a breaker is tripping because of an overload condition, it will usually be after several seconds, minutes, or even hours of operation. It will not be instantaneous unless someone installed the wrong breaker or fuse and used an “instantaneous trip” instead of a typical “slow - blow” or slow -acting type. That would be quite rare.

A combination of visual inspection, isolation, and ohm measurement to ground and megaohm/hi-pot tests or hot verification as needed is the best way to diagnose a short to-ground (ground fault). Ground faults can be extremely dangerous and cause injury or death. In many cases, local codes require the use of a ground fault circuit interrupter (GFCI) in rooms where ground faults are common.

You can learn more about GFCIs HERE.

Leg to Leg Short (Bucking Phases) When you have two legs of power with different sine wave patterns, such as a 240V single-phase or three-phase power, you must prevent the legs from coming into contact except through a load. If they do come in contact, there will be an enormous transfer of energy and a significant arc. This can happen when two wires rub out, when switchgear becomes compromised, or within a motor.

Ground Fault A ground fault is a short circuit (no load path) between an energized circuit and equipment ground. A ground fault is the most common cause of instantaneous breaker tripping. In most ground-fault situations, there will be very high amperage, very quickly resulting in a breaker that trips right away. Common cases would include a shorted motor, such as a shorted compressor or a rubbed-out wire.