Gas - Unit M Flashcards
List the four electrical circuits on a forced warm-air furnace.
Combustion safety circuit.
Control circuit[][][][][][][][][][][]
Fan circuit[][][][][][][][][][][][][]]
Transformer circuit[][][][][][]]
True or False?
All control systems have these four basic circuits:
Combustion Safety Circuit.
Control Circuit[][][][][][][][][][][]
Fan Circuit[][][][][][][][][][][][][][]]
Transformer Circuit[][][][][][][][]
False.
Identify the basic components of a Combustion Safety Circuit.
Safety shut off valve (switch).
Thermocouple[][][][][][][][][][][][][]
How many volts are generated by a single thermocouple?
25 - 30 mV.
Describe a thermopile and list the two types.
When one or more thermocouple is wired in series, the unit is called a thermopile. Coaxial and Modern.
Describe the difference between 100% safe switches and non-100% safe switches.
100% Safe: Shut off gas to burner and pilot.
Non-100% Safe: Shut off gas to burner[][][][]]
True or False?
Safety switches are commonly used on equipment having an input of over 400 cu ft/h.
True.
Explain why switches are always put in the hot leg of a circuit.
If in the hot leg, there will be no electricity connected to the appliance and no shock hazard when working on appliance when switch is off.
True or False?
A single pole, single throw switch can energize one of two different circuits or loads.
False.
True or False?
A double pole, single throw switch can open and close two independent circuits at the same time.
True.
True or False?
A normally open flow switch is open when current flows.
False.
True or False?
The high-limit switch is a normally closed switch that opens if overheating occurs.
True.
True or False?
An operating aquastat senses water temperature and de-energizes the main gas valve when the tempurature reaches the set point.
True.
True or False?
A high-limit aquastat is a back up to the operating aquastat but is adjusted to a higher set point.
True.
What will happen if the voltage designation of the gas valve’s magnetic coil does not match the power supply?
The valve coil may burn out or not operate the valve.
True or False?
A transformer is only used on alternating current.
True.
True or False?
The primary and secondary coils of a transformer are not electrically connected.
True.
True or False?
The primary and secondary coils of a transformer are magnetically connected.
True.
True or False?
In a step-down transformer, the secondary coil has less voltage than the primary.
True.
True or False?
In a step-down transformer, the secondary coil has more turns than the primary.
False.
What is the rating of a transformer that drops voltage from 110V to 24V with an ouput of 3 1/3 amps?
24 Volts x 3 1/3 Amps = 80 VA.
True or False?
The rating of a transformer should be less than the load to which it is attached.
False.
True or False?
The fan switch turns on the fan as soon as the thermostat calls for heat.
False.
True or False?
The fan switch is activated by heat.
True.
True or False?
The fan-on set point tempurature will be reached some time after the gas valve opens.
True.
True or False?
The fan-off set point tempurature will turn off the fan if the furnace gets too hot.
False.
True or False?
The fan-off set point will be reached after the gas valve closes.
True.
True or False?
When the fan-off set point is reached, the fan stops.
True.
True or False?
If the motor pulley on a belt drive fan motor is made larger, the fan will run faster and deliver more air.
True.
List four types of electrical drawings.
Block and one-line.
Pictorial[][][][][][][][][][]
Schematic[][][][][][][][]
Wiring[][][][][][][][][][][]]
Which type of drawing shows the components of an electrical circuit in their actual likeness?
Pictorial.
Which type of drawing shows electrical components as blocks and arranges them in a logical sequence of events?
Block and one-line.
Which type of drawing is considered to be a map of the circuits?
Wiring.
Which type of drawing shows the electrical relationship between the components in a circuit?
Schematic.
Which type of drawing uses symbols to represent the switches and loads and shows each circuit as a rung of a ladder?
Ladder.
List the components of an appliance branch circuit.
Appliance dissconnect switch.
Appliance junction box[][][][][][][]
Breaker (overcurrent protection device).
Describe the two types of circuit breakers.
Magnetic.
Thermal[]
To dissconnect power from the appliance in an emergency or for service and repair is the definition of?
Disconnect switch.
To provide an approved location to join line voltage wiring is the definition of?
Junction box.
