When setting the relay characteristic/torque angle for the three phase directional overcurrent element, a positive angle setting was specified. This was due to the fact that we consider as polarising voltage, the phase voltage value in quadrature of the current under fault conditions. With directional earth fault protection, the residual current under fault conditions lies at an angle lagging the polarising residual earth fault voltage.
QO-HM and QOB-HM high-magnetic circuit breakers are recommended for area lighting (such as
athletic fields, parking lots, and outdoor signs), when using lamps of inherent high inrush current,
individual dimmer applications or other applications where high inrush currents exceed standard
tripping conditions. These circuit breakers are available in one-pole 15 and 20 A ratings only. QO-HM
and QOB-HM circuit breakers are physically interchangeable with standard QO and QOB circuit
breakers and accommodate the complete range of QO accessories.
QO-HM and QOB-HM circuit breakers are manufactured with the magnetic trip point calibrated at a
much higher level than standard QO and QOB circuit beakers, as shown in Table 3.
QO-HID and QOB-HID High Intensity Discharge Circuit Breakers
QO-HID and QOB-HID circuit breakers are for use in high intensity discharge (HID) lighting systems,
such as systems using mercury vapor, metal halide or high-pressure sodium lighting units. These
circuit breakers are designed to handle the high inductive loads, harmonic currents and cycling which
are inherent in HID lighting systems. QO-HID and QOB-HID circuit breakers are physically
interchangeable with standard QO circuit breakers and accommodate the complete range of QO
accessories.
QO-HID and QOB-HID circuit breakers are manufactured with larger contacts than standard QO and
QOB circuit breakers to allow switching of high inductive loads. They also have magnetic
characteristics similar to QO-HM and QOB-HM high-magnetic circuit breakers to allow the circuit
breaker to hold in against the high starting inrush currents which are typical in HID lighting systems.
QO and QOB Miniature Switches
Miniature switches are intended for use as disconnecting devices only. They provide no overcurrent
protection. QO and QOB switches are UL Certified for use on circuits capable of delivering not more
than 10 kA when protected by an equivalent rated circuit breaker or fuse. These switches are available
in 60 and 100 A rating.
QO and QOB switches are available with auxiliary switches only. (Shunt trip and bell alarm electrical
accessories are not available on QO and QOB miniature switches.) QO and QOB switches are
available with the complete range of handle accessories.
QOK and QOBK Key-Operated Circuit Breakers
Key-operated QOK and QOBK circuit breakers provide an alternative means for turning a circuit
breaker ON or OFF, as well as for resetting a tripped circuit breaker. The circuit breaker is turned on,
off or reset with a special key included with the circuit breaker. Key-operated circuit breakers are
available in one-pole construction only and can be mounted in any one-pole space which will accept a
standard QO circuit breaker. These circuit breakers are available in 10–30 A ratings, with interrupting
ratings of 10 kA at 120 Vac.
Replacement keys are available separately. Factory-installed or field-installable accessories are not
available on key-operated circuit breakers.
