CFESA ELECTRICAL QUESTIONS & ANSWERS
What do the following prefixes mean? Micro,kilo,mega,milli - answer -1/1,000,000,
1000, 1,000,000, 1/1000
If you know the wattage and voltage, how do you determine the current? - answer -
divide the wattage by the voltage
If you know the voltage and current how do you determine the wattage? - answer -
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? - answer -.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? - answer -4160 watts
How much voltage is in one hot line? - answer -none
What happens to current in a parallel circuit? - answer -it divides across resistances
What happens to voltage across the loads in a parallel circuit? - answer -stays the
same
What happens to the voltage across the loads in a series circuit? - answer -it divides
across the resistances
What happens to the current in a series circuit? - answer -it stays the same everywhere
In a parallel circuit the total resistance of the circuit will always be less than what
resistance? - answer -the smallest resistance
How do you find the total resistance of a series circuit? - answer -add the resistances
together
How do you find the total resistance of a parallel circuit? - answer -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? - answer -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? - answer -
240 volts
,What is the advantage of using higher voltages? - answer -lower current and wire size
Is there a negative and positive line in ac power supplies? - answer -no
What is the voltage between a hot line and ground on a 240 volt delta power supply -
answer -no usable voltage
What is the voltage between any two hot lines of a 230 volt grounded delta power
supply - answer -230v
Draw a diagram of a 230 volt grounded delta power supply. Label all of the voltages and
the wild leg - answer -
What is the wild leg? - answer -leg with higher than 120v to ground or neutral
What danger is the wild leg? - answer -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? - answer -115v
How do you determine which hot line is the wild leg in a 250 volt grounded delta power
supply? - answer -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? - answer -crossing the hot lines and supplying the wild
leg to the wrong terminal in the unit.
Why is a "wye" power supply so versatile - answer -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? -
answer -208v
What is the voltage between any hot line and neutral or ground in a 208 volt wye power
supply? - answer -120v
What is the voltage from any hot line to ground or neutral, on a 480 volt wye power
supply? - answer -277v
What is the voltage between two hot lines in a 230-volt system? - answer -230v
What is the voltage between two hot lines in a 208-volt system? - answer -208v
,What is the voltage between a hot line and a neutral in a 230-volt single phase supply? -
answer -115v
What is the voltage between a hot line and a neutral in a 208-volt single phase supply? -
answer -120v
What is the accepted maximum voltage difference between the name plate voltage and
the supplied voltage? - answer -+ or - 10%
What is the voltage between any two hot lines of a 230 volt delta power supply? -
answer -230v
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? - answer -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? - answer -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? - answer -1
Approximately how much will the wattage increase on a 208v piece of equipment if it is
connected to 240v supply? - answer -33%
Approximately how much will the rated wattage decrease if a 240v unit is connected to
a 208v power supply? - answer -25%
What damage could potentially be caused to the supply wiring if 208v unit is connected
to a 240v supply? - answer -higher wattage created will damage heaters or other
components
How can the cooking characteristics of equipment be changed by a low supply voltage?
- answer -slow recovery time, uneven cooking
When is the most opportune time to discover a low or high voltage problem? - answer -
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? - answer -yes
How many resistances must you have to have a balanced load? - answer -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? - answer -amperage = wattage / (voltage x 1.732)
How can you tell if a piece of equipment will be a balanced load or not? - answer -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? - answer -jim, the
single phase motor unbalances the load
Electricity will always follow what path? - answer -path of least resistance
Why should all equipment be grounded? - answer -safety and code
How should the earth ground from the main fuse or breaker panel be connected? -
answer -from grounding bus bar to ground rod or metal water pipe
In order for a receptacle to be properly grounded, the ground wire must run to where? -
answer -all the way back to the panel
How much resistance should you read from a neutral connection to a ground
connection? - answer -0 ohms
What is the difference between neutral and ground? - answer -the neatural normall
carries current, the ground does not
Can you get shocked from the casing on a piece of equipment if it is properly grounded?
- answer -no
Ground wires must always be what colors? - answer -green, green with yellow tracer,
or bare white
How much current does a short circuit draw? - answer -infinite amps
If a cord on a unit is shorted, can it damage the power switch on the piece of
equipment? - answer -no
If a heating element on an electric grill is shorted could it damage the thermostat? -
answer -yes
If a power switch is shorted on a heat lamp could it damage the heating element? -
answer -no
When checking voltage, you must touch your meter leads where? - answer -across the
load you are measuring
What do the following prefixes mean? Micro,kilo,mega,milli - answer -1/1,000,000,
1000, 1,000,000, 1/1000
If you know the wattage and voltage, how do you determine the current? - answer -
divide the wattage by the voltage
If you know the voltage and current how do you determine the wattage? - answer -
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? - answer -.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? - answer -4160 watts
How much voltage is in one hot line? - answer -none
What happens to current in a parallel circuit? - answer -it divides across resistances
What happens to voltage across the loads in a parallel circuit? - answer -stays the
same
What happens to the voltage across the loads in a series circuit? - answer -it divides
across the resistances
What happens to the current in a series circuit? - answer -it stays the same everywhere
In a parallel circuit the total resistance of the circuit will always be less than what
resistance? - answer -the smallest resistance
How do you find the total resistance of a series circuit? - answer -add the resistances
together
How do you find the total resistance of a parallel circuit? - answer -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? - answer -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? - answer -
240 volts
,What is the advantage of using higher voltages? - answer -lower current and wire size
Is there a negative and positive line in ac power supplies? - answer -no
What is the voltage between a hot line and ground on a 240 volt delta power supply -
answer -no usable voltage
What is the voltage between any two hot lines of a 230 volt grounded delta power
supply - answer -230v
Draw a diagram of a 230 volt grounded delta power supply. Label all of the voltages and
the wild leg - answer -
What is the wild leg? - answer -leg with higher than 120v to ground or neutral
What danger is the wild leg? - answer -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? - answer -115v
How do you determine which hot line is the wild leg in a 250 volt grounded delta power
supply? - answer -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? - answer -crossing the hot lines and supplying the wild
leg to the wrong terminal in the unit.
Why is a "wye" power supply so versatile - answer -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? -
answer -208v
What is the voltage between any hot line and neutral or ground in a 208 volt wye power
supply? - answer -120v
What is the voltage from any hot line to ground or neutral, on a 480 volt wye power
supply? - answer -277v
What is the voltage between two hot lines in a 230-volt system? - answer -230v
What is the voltage between two hot lines in a 208-volt system? - answer -208v
,What is the voltage between a hot line and a neutral in a 230-volt single phase supply? -
answer -115v
What is the voltage between a hot line and a neutral in a 208-volt single phase supply? -
answer -120v
What is the accepted maximum voltage difference between the name plate voltage and
the supplied voltage? - answer -+ or - 10%
What is the voltage between any two hot lines of a 230 volt delta power supply? -
answer -230v
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? - answer -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? - answer -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? - answer -1
Approximately how much will the wattage increase on a 208v piece of equipment if it is
connected to 240v supply? - answer -33%
Approximately how much will the rated wattage decrease if a 240v unit is connected to
a 208v power supply? - answer -25%
What damage could potentially be caused to the supply wiring if 208v unit is connected
to a 240v supply? - answer -higher wattage created will damage heaters or other
components
How can the cooking characteristics of equipment be changed by a low supply voltage?
- answer -slow recovery time, uneven cooking
When is the most opportune time to discover a low or high voltage problem? - answer -
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? - answer -yes
How many resistances must you have to have a balanced load? - answer -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? - answer -amperage = wattage / (voltage x 1.732)
How can you tell if a piece of equipment will be a balanced load or not? - answer -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? - answer -jim, the
single phase motor unbalances the load
Electricity will always follow what path? - answer -path of least resistance
Why should all equipment be grounded? - answer -safety and code
How should the earth ground from the main fuse or breaker panel be connected? -
answer -from grounding bus bar to ground rod or metal water pipe
In order for a receptacle to be properly grounded, the ground wire must run to where? -
answer -all the way back to the panel
How much resistance should you read from a neutral connection to a ground
connection? - answer -0 ohms
What is the difference between neutral and ground? - answer -the neatural normall
carries current, the ground does not
Can you get shocked from the casing on a piece of equipment if it is properly grounded?
- answer -no
Ground wires must always be what colors? - answer -green, green with yellow tracer,
or bare white
How much current does a short circuit draw? - answer -infinite amps
If a cord on a unit is shorted, can it damage the power switch on the piece of
equipment? - answer -no
If a heating element on an electric grill is shorted could it damage the thermostat? -
answer -yes
If a power switch is shorted on a heat lamp could it damage the heating element? -
answer -no
When checking voltage, you must touch your meter leads where? - answer -across the
load you are measuring
