CFESA Electrical - Questions And Step-by-Step Answers
What do the following prefixes mean? Micro,Kilo,Mega,Milli Right Ans -
1/1,000,000, 1000, 1,000,000, 1/1000
If you know the wattage and voltage, how do you determine the current?
Right Ans - Divide the wattage by the voltage
If you know the voltage and current how do you determine the wattage?
Right Ans - Multiply voltage times current
If a circuit is supplied with 100 volts and the total resistance of the circuit is
200 ohms, how much current will the circuit draw? Right Ans - .5 amps
If a piece of equipment is supplied 208 volts and the amp meter clamped to
the hot line reads 20 amps, what is the wattage of the load? Right Ans -
4160 Watts
How much voltage is in one hot line? Right Ans - None
What happens to current in a parallel circuit? Right Ans - It divides across
resistances
what happens to voltage across the loads in a parallel circuit? Right Ans -
stays the same
what happens to the voltage across the loads in a series circuit? Right Ans -
it divides across the resistances
what happens to the current in a series circuit? Right Ans - It stays the
same everywhere
in a parallel circuit the total resistance of the circuit will always be less than
what resistance? Right Ans - the smallest resistance
how do you find the total resistance of a series circuit? Right Ans - add the
resistances together
,how do you find the total resistance of a parallel circuit? Right Ans - 1/RT =
1/R1 + 1/R2 + 1/R3 ...
If a circuit is wired parallel, and the supply voltage is 120 volts, each load must
be rated at what voltage? Right Ans - 120 volts
if a circuit has two elements wired in series, and each is rated at 120 volts,
what voltage must be supplied to the circuit in order for the elements to heat
at full power? Right Ans - 240 volts
What is the advantage of using higher voltages? Right Ans - Lower Current
and wire size
Is there a negative and positive line in AC power supplies? Right Ans - No
What is the voltage between two hot lines in a 230-volt system? Right Ans -
230V
What is the voltage between two hot lines in a 208-volt system? Right Ans -
208V
What is the voltage between a hot line and a neutral in a 230-volt single phase
supply? Right Ans - 115V
What is the voltage between a hot line and a neutral in a 208-volt single phase
supply? Right Ans - 120V
What is the accepted maximum voltage difference between the name plate
voltage and the supplied voltage? Right Ans - + or - 10%
What is the voltage between any two hot lines of a 230 volt delta power
supply? Right Ans - 230V
what is the voltage between a hot line and ground on a 240 volt delta power
supply Right Ans - No usable voltage
what is the voltage between any two hot lines of a 230 volt grounded delta
power supply Right Ans - 230V
,draw a diagram of a 230 volt grounded delta power supply. label all of the
voltages and the wild leg Right Ans -
what is the wild leg? Right Ans - leg with higher than 120v to ground or
neutral
what danger is the wild leg? Right Ans - high voltage that will damage 120v
component in the circuit
what is the voltage between either of the non wild leg hot lines and neutral in
a 230 volt grounded delta system? Right Ans - 115v
how do you determine which hot line is the wild leg in a 250 volt grounded
delta power supply? Right Ans - the one that does not measure 120 volts to
neutral or ground
what danger is there when replacing a three phase circuit breaker in a 230
volt grounded delta power supply? Right Ans - crossing the hot lines and
supplying the wild leg to the wrong terminal in the unit.
Why is a "WYE" power supply so versatile Right Ans - can get 120v and
208v as well as single and three phase
What is the voltage between any two hot lines in a 208 volt WYE power
supply? Right Ans - 208v
What is the voltage between any hot line and neutral or ground in a 208 volt
WYE power supply? Right Ans - 120v
What is the voltage from any hot line to ground or neutral, on a 480 volt WYE
power supply? Right Ans - 277v
if you had a commercial building and you had a three phase supply to your
building how many different incoming power supplies would you need if the
incoming three phase supply was three phase delta? Right Ans - 2
if you had a commercial building and you had a three phase supply to your
building, how many different incoming power supplies would you need if the
, incoming three phase supply was three phase grounded delta? Right Ans -
1
if you had a commercial building and you had a three phase supply to your
building how many different incoming power supplies would you need if the
incoming three phase supply was three phase WYE 208v? Right Ans - 1
approximately how much will the wattage increase on a 208v piece of
equipment if it is connected to 240v supply? Right Ans - 33%
approximately how much will the rated wattage decrease if a 240v unit is
connected to a 208v power supply? Right Ans - 25%
what damage could potentially be caused to the supply wiring if 208v unit is
connected to a 240v supply? Right Ans - higher wattage created will
damage heaters or other components
how can the cooking characteristics of equipment be changed by a low supply
voltage? Right Ans - slow recovery time, uneven cooking
when is the most opportune time to discover a low or high voltage problem?
Right Ans - at equipment startup, before the unit is energized
can high voltage result in and overheating problem when trying to control the
temp of an oven? Right Ans - yes
how many resistances must you have to have a balanced load? Right Ans -
3 or a multiple of 3
what is the formula for calculating the current draw from the wattage and
voltage on a three phase balanced load? Right Ans - amperage = wattage /
(voltage X 1.732)
how can you tell if a piece of equipment will be a balanced load or not?
Right Ans - must have 3 or a multiple of three loads
Joe says a convection oven that has three heating elements, and a single phase
blower motor is a balanced three phase load. Jim says it is not. Who is right?
Right Ans - Jim, sing phase motor unbalances the load
What do the following prefixes mean? Micro,Kilo,Mega,Milli Right Ans -
1/1,000,000, 1000, 1,000,000, 1/1000
If you know the wattage and voltage, how do you determine the current?
Right Ans - Divide the wattage by the voltage
If you know the voltage and current how do you determine the wattage?
Right Ans - Multiply voltage times current
If a circuit is supplied with 100 volts and the total resistance of the circuit is
200 ohms, how much current will the circuit draw? Right Ans - .5 amps
If a piece of equipment is supplied 208 volts and the amp meter clamped to
the hot line reads 20 amps, what is the wattage of the load? Right Ans -
4160 Watts
How much voltage is in one hot line? Right Ans - None
What happens to current in a parallel circuit? Right Ans - It divides across
resistances
what happens to voltage across the loads in a parallel circuit? Right Ans -
stays the same
what happens to the voltage across the loads in a series circuit? Right Ans -
it divides across the resistances
what happens to the current in a series circuit? Right Ans - It stays the
same everywhere
in a parallel circuit the total resistance of the circuit will always be less than
what resistance? Right Ans - the smallest resistance
how do you find the total resistance of a series circuit? Right Ans - add the
resistances together
,how do you find the total resistance of a parallel circuit? Right Ans - 1/RT =
1/R1 + 1/R2 + 1/R3 ...
If a circuit is wired parallel, and the supply voltage is 120 volts, each load must
be rated at what voltage? Right Ans - 120 volts
if a circuit has two elements wired in series, and each is rated at 120 volts,
what voltage must be supplied to the circuit in order for the elements to heat
at full power? Right Ans - 240 volts
What is the advantage of using higher voltages? Right Ans - Lower Current
and wire size
Is there a negative and positive line in AC power supplies? Right Ans - No
What is the voltage between two hot lines in a 230-volt system? Right Ans -
230V
What is the voltage between two hot lines in a 208-volt system? Right Ans -
208V
What is the voltage between a hot line and a neutral in a 230-volt single phase
supply? Right Ans - 115V
What is the voltage between a hot line and a neutral in a 208-volt single phase
supply? Right Ans - 120V
What is the accepted maximum voltage difference between the name plate
voltage and the supplied voltage? Right Ans - + or - 10%
What is the voltage between any two hot lines of a 230 volt delta power
supply? Right Ans - 230V
what is the voltage between a hot line and ground on a 240 volt delta power
supply Right Ans - No usable voltage
what is the voltage between any two hot lines of a 230 volt grounded delta
power supply Right Ans - 230V
,draw a diagram of a 230 volt grounded delta power supply. label all of the
voltages and the wild leg Right Ans -
what is the wild leg? Right Ans - leg with higher than 120v to ground or
neutral
what danger is the wild leg? Right Ans - high voltage that will damage 120v
component in the circuit
what is the voltage between either of the non wild leg hot lines and neutral in
a 230 volt grounded delta system? Right Ans - 115v
how do you determine which hot line is the wild leg in a 250 volt grounded
delta power supply? Right Ans - the one that does not measure 120 volts to
neutral or ground
what danger is there when replacing a three phase circuit breaker in a 230
volt grounded delta power supply? Right Ans - crossing the hot lines and
supplying the wild leg to the wrong terminal in the unit.
Why is a "WYE" power supply so versatile Right Ans - can get 120v and
208v as well as single and three phase
What is the voltage between any two hot lines in a 208 volt WYE power
supply? Right Ans - 208v
What is the voltage between any hot line and neutral or ground in a 208 volt
WYE power supply? Right Ans - 120v
What is the voltage from any hot line to ground or neutral, on a 480 volt WYE
power supply? Right Ans - 277v
if you had a commercial building and you had a three phase supply to your
building how many different incoming power supplies would you need if the
incoming three phase supply was three phase delta? Right Ans - 2
if you had a commercial building and you had a three phase supply to your
building, how many different incoming power supplies would you need if the
, incoming three phase supply was three phase grounded delta? Right Ans -
1
if you had a commercial building and you had a three phase supply to your
building how many different incoming power supplies would you need if the
incoming three phase supply was three phase WYE 208v? Right Ans - 1
approximately how much will the wattage increase on a 208v piece of
equipment if it is connected to 240v supply? Right Ans - 33%
approximately how much will the rated wattage decrease if a 240v unit is
connected to a 208v power supply? Right Ans - 25%
what damage could potentially be caused to the supply wiring if 208v unit is
connected to a 240v supply? Right Ans - higher wattage created will
damage heaters or other components
how can the cooking characteristics of equipment be changed by a low supply
voltage? Right Ans - slow recovery time, uneven cooking
when is the most opportune time to discover a low or high voltage problem?
Right Ans - at equipment startup, before the unit is energized
can high voltage result in and overheating problem when trying to control the
temp of an oven? Right Ans - yes
how many resistances must you have to have a balanced load? Right Ans -
3 or a multiple of 3
what is the formula for calculating the current draw from the wattage and
voltage on a three phase balanced load? Right Ans - amperage = wattage /
(voltage X 1.732)
how can you tell if a piece of equipment will be a balanced load or not?
Right Ans - must have 3 or a multiple of three loads
Joe says a convection oven that has three heating elements, and a single phase
blower motor is a balanced three phase load. Jim says it is not. Who is right?
Right Ans - Jim, sing phase motor unbalances the load
