System Protection
When replacing a fuse you must match the:
What is Volt, amp, instantaneous current, and physical size.
What are 2 categories that switches be divided into
What is line voltage and low voltage
Compared to mechanical thermostats, digital thermostats:
Maintain closer temperature control.
This component uses the properties of AC induction to step up or step-down voltage for particular HVAC applications
What is Transformer
What is used as the sensing element in a mechanical humidistat
What is A nylon ribbon or hair
Overloads are designed to protect against:
Excessive current
How are switches rated
What is by thier application
Low-voltage thermostats normally operate on what voltage
what is 24V
What is the purpose of a standard control transformer is to
What is Reduce line voltage to 24 V for HVACR control systems
Two common pressure-sensing devices used in pressure controls are:
The bellows and the diaphragm
A fuse protects an electrical circuit by:
Melting when excessive current flows through it, opening the circuit
What two manual switches are found on most low-voltage thermostats
What is A systems switch and a fan switch
How does a remote bulb thermostat work?
Pressure in the bulb rises and falls with temperature
Do transformers operate more or less efficiently when fully loaded?
They are more effecent when they are fully loaded
What is the cut-out for a close-on-rise pressure switch with a cut-in setting of 45 psig and a differential of setting of 20 psi?
What is 45 – 20 = 25 psig
What is the advantage of a circuit breaker as compared to a fuse?
The advantage of a circuit breaker over a fuse is that it can be manually reset at the electrical service panel after an overload, rather than replaced
What is a proximity switch
Proximity switches often limit motion and are often operated by the movement of a mechanical device.
What type of applications is a close-on-rise thermostat normally used for?
A close-on-rise thermostat is used for cooling.
The primary winding of a 120 V transformer has 200 turns. The secondary winding has 20 turns. What is the secondary winding voltage?
12V
On a close-on-rise pressure switch, what should the differential be set for a cut-out of 15 psig if the cut-in setting is 25 psig?
What is 25 – 15 = 10 psi
What type of fuses should be used to protect motor circuits?
What is Dual-element time delay fuse
What do modern electronic thermostats use to sense temperature?
What is Thermistors.