How is electric heat produced?
It is produced by converting electrical energy to heat. A particular material with a known resistance is placed in a circuit. The material does not conduct electricity easily and the electron flow produces heat.
Name one type of material used in resistance wire.
Nichrome or nickel chromium.
T or F - electric heat is cheaper to operate than other sources of heat because it is so efficient.
False- electric heat is efficient but it is more expensive to operate.
Why is electric heat considered efficient?
Very little electrical energy is lost from the meter to the heating element.
Why is electric heat expensive?
It takes a large quantity of electrical energy to produce heat.
Why is an electrical heat system attractive to most purchasers?
Electrical heating systems usually cost less than other systems and installation and maintenance is usually less expensive.
How do portable space heaters with glowing coils heat up a room?
The coils transfer heat by radiation to objects in front of the heater.
How do other portable space heaters heat up room.
Other heaters used forced-convection heat to move heated air into the space.
Describe a radiant electric heating panel.
It is a gypsum board with wire heating circuits running throughout it. They are usually installed in ceilings and are controlled by room thermostats.
What must heating panels have behind or above them.
They need to have good insulation to keep heat from escaping.
What type of heat is used by electric baseboard heaters?
They use natural draft convection. Air enters the bottom of the unit, passes over the heating element, is heating and then rises up into the room.
Where are electric baseboard heaters usually installed.
They can usually be found on the wall just above the floor or carpet.
What type of thermostat controls electric baseboard units.
They are usually individual room thermostats and line-voltage.
Where are unit heaters usually located?
They are usually suspended from the ceiling and use a propeller fan to force air across the elements into the space being heated.
What is an electric hydronic system similar too?
They are similar to electric domestic water heater.
How do central forced-air electric furnaces get heat to the rooms?
They use ductwork to distribute the heated air to the rooms.
Are central heaters controlled by several room thermostats or one thermostat?
It is controlled by a single thermostat.
What is an interlock and why are they needed?
An interlock system will not allow power to reach the heating element unless the fan is operating. This keeps the element from overheating and possibly cause a fire.
What are the three common controls in an electric heating application?
Thermostats, sequencers and contactors.
Why is a low-voltage thermostat used for sequencers and contactors?
They are compact, very responsive, safe, easy to install and easy to troubleshoot.
When a thermostat has two power supplies, what does it need and why?
It needs to have an isolated subbase. It may have 2 power supplies if air conditioning is added after the furnace was installed. Each system will have its own low-voltage power supply.
If one power supply is used for both system, what must be done inside the thermostat for power.
A jumper is required from the R terminal to the "4" terminal. The 4 terminal is the assigned to the heating.
How is the setting for the heat anticipator determined?
It is determined by adding all the current draw in the 24V heating circuit that passes through the thermostat control and heat anticipator.
Why do electric heating furnaces have several stages when turning on the electric heat.
To prevent a high load coming on all at once. By turning on in stages, the electrical load is gradually increased.
What is used to gradually turn on the electric heaters?
A sequencer is used. It uses low-voltage to heat a bimetal strip and warp it. As it warps, it closes electrical contacts and turns on electric heaters with a time delay.
How many stages can a package sequencer have for turning on strip heat?
They have the ability for 3 stages. Some sequencers may have 5 circuits- three heat circuits, a fan circuit and a circuit to pass power to another sequencer if needed.
What are two ways that manufacturers illustrate electrical circuits?
Schematic (also known as line wire or ladder) - they show the current path to the components.
Pictoral - shows the location of each component as it actually appears.
What is a limit switch do?
It is a safety device that shuts off the unit if high temperature occurs. It opens when under excessive heat.
Safety and operating devices:
A) consume power
B) pass power
C) both consume and pass power
C) they can consume power and do work and can pass power.
Give an example of a device that consumes power and passes power.
A sequencer uses low-voltage electrical energy to warp the bimetal inside it. It then passes power to devices that are in the high-voltage circuit.
A contactor uses low-voltage electrical energy to magnetize the solenoid and then pass power to high-voltag
Power-passing devices are wired in ______ while power-consuming devices are wired in ______ with each other.
Series (mnemonic is SerieS/paSSing)
Parallel
What happens to a limit switch after it opens?
Limit switches are usually an automatic reset switch when the temperature cools.
If a fusible link melts, what must be done to get it back online?
It must be replaced.
With regards to the operation of the fan motor, when does it need to turn on and turn off?
It must run before the furnace gets too hot and must continue to run until the furnace cools down.
How are contacts in a sequencer and relay contacts wired, series or parallel?
They are wired in series because the contacts are power-passing.
What is the formula to calculate sensible heat in Btu/h?
Qs = 1.08 x cfm x TD
What is the formula to calculate Watts?
Watts = Amps x Volts
How many Btus are in a watt?
3.413
What is the formula to calculate Btu/h?
Watts x 3.413
What is a fuseable link?
It works like an in-line fuse to protect the system from high amps or high temperature.
What causes hot spots on electric heat elements?
They are caused by a lack of air flow.
Why are contactors not used to start up electric heat furnaces?
They do not have capability to delay startup so all heat will start at one time, causing a large inrush of power. They are noisy because of the magnetic coil when they snap in. They may rattle or hum.
What is usually installed in ductwork that ensures the fan is blowing
A system switch or sailswitch.
Why is it better to use a sequencer than a contactor to turn on heat elements?
Contactors are noisy and do not have capability to space out the heating elements. They turn on all at the same time.
If you know the watts a heating element has and the voltage for the circuit, how can you figure out the individual fuse requirements for the element?
Take the number of watts for the element and divide by the voltage.
Example 7500W / 240V = 31.3A.
then multiple that figure by 125% and round up to the next figure
Example - 31.3A element x 125% = 39.1A which rounds up to 40A fuse.
Name six circumstances can cause a fuseable link or high limit switch to trip
1. Bad blower/motor/capacitor
2. Dirty filter/obstruction in return
3. Too many closed registers
4. Loose electrical connection
5. Undersized blower motor
6. Improper fuse size.
How are electric heating elements rated, in KW or BTUs?
In KW
Is the sail switch wired in series or parallel with the heat coil?
It is wired in series.
At what temperature are fuseable links set to?
They are set to melt at a temperature that is higher than the cutout temperature of the limit switch.
What is the table for wire gage and amps for first 500 feet?
6 - 50A
8 - 40A
10 - 30A
12 - 20A
14 - 15A
16 - 10A
How is electric heat produced?
It is produced by converting electrical energy to heat. A particular material with a known resistance is placed in a circuit. The material does not conduct electricity easily and the electron flow produces heat.
Name one type of material used in resistance wire.
Nichrome or nickel chromium.
T or F - electric heat is cheaper to operate than other sources of heat because it is so efficient.
False- electric heat is efficient but it is more expensive to operate.
Why is electric heat considered efficient?
Very little electrical energy is lost from the meter to the heating element.
Why is electric heat expensive?
It takes a large quantity of electrical energy to produce heat.
Why is an electrical heat system attractive to most purchasers?
Electrical heating systems usually cost less than other systems and installation and maintenance is usually less expensive.
How do portable space heaters with glowing coils heat up a room?
The coils transfer heat by radiation to objects in front of the heater.
How do other portable space heaters heat up room.
Other heaters used forced-convection heat to move heated air into the space.
Describe a radiant electric heating panel.
It is a gypsum board with wire heating circuits running throughout it. They are usually installed in ceilings and are controlled by room thermostats.
What must heating panels have behind or above them.
They need to have good insulation to keep heat from escaping.
What type of heat is used by electric baseboard heaters?
They use natural draft convection. Air enters the bottom of the unit, passes over the heating element, is heating and then rises up into the room.
Where are electric baseboard heaters usually installed.
They can usually be found on the wall just above the floor or carpet.
What type of thermostat controls electric baseboard units.
They are usually individual room thermostats and line-voltage.
Where are unit heaters usually located?
They are usually suspended from the ceiling and use a propeller fan to force air across the elements into the space being heated.
What is an electric hydronic system similar too?
They are similar to electric domestic water heater.
How do central forced-air electric furnaces get heat to the rooms?
They use ductwork to distribute the heated air to the rooms.
Are central heaters controlled by several room thermostats or one thermostat?
It is controlled by a single thermostat.
What is an interlock and why are they needed?
An interlock system will not allow power to reach the heating element unless the fan is operating. This keeps the element from overheating and possibly cause a fire.
What are the three common controls in an electric heating application?
Thermostats, sequencers and contactors.
Why is a low-voltage thermostat used for sequencers and contactors?
They are compact, very responsive, safe, easy to install and easy to troubleshoot.
When a thermostat has two power supplies, what does it need and why?
It needs to have an isolated subbase. It may have 2 power supplies if air conditioning is added after the furnace was installed. Each system will have its own low-voltage power supply.
If one power supply is used for both system, what must be done inside the thermostat for power.
A jumper is required from the R terminal to the "4" terminal. The 4 terminal is the assigned to the heating.
How is the setting for the heat anticipator determined?
It is determined by adding all the current draw in the 24V heating circuit that passes through the thermostat control and heat anticipator.
Why do electric heating furnaces have several stages when turning on the electric heat.
To prevent a high load coming on all at once. By turning on in stages, the electrical load is gradually increased.
What is used to gradually turn on the electric heaters?
A sequencer is used. It uses low-voltage to heat a bimetal strip and warp it. As it warps, it closes electrical contacts and turns on electric heaters with a time delay.
How many stages can a package sequencer have for turning on strip heat?
They have the ability for 3 stages. Some sequencers may have 5 circuits- three heat circuits, a fan circuit and a circuit to pass power to another sequencer if needed.
What are two ways that manufacturers illustrate electrical circuits?
Schematic (also known as line wire or ladder) - they show the current path to the components.
Pictoral - shows the location of each component as it actually appears.
What is a limit switch do?
It is a safety device that shuts off the unit if high temperature occurs. It opens when under excessive heat.
Safety and operating devices:
A) consume power
B) pass power
C) both consume and pass power
C) they can consume power and do work and can pass power.
Give an example of a device that consumes power and passes power.
A sequencer uses low-voltage electrical energy to warp the bimetal inside it. It then passes power to devices that are in the high-voltage circuit.
A contactor uses low-voltage electrical energy to magnetize the solenoid and then pass power to high-voltag
Power-passing devices are wired in ______ while power-consuming devices are wired in ______ with each other.
Series (mnemonic is SerieS/paSSing)
Parallel
What happens to a limit switch after it opens?
Limit switches are usually an automatic reset switch when the temperature cools.
If a fusible link melts, what must be done to get it back online?
It must be replaced.
With regards to the operation of the fan motor, when does it need to turn on and turn off?
It must run before the furnace gets too hot and must continue to run until the furnace cools down.
How are contacts in a sequencer and relay contacts wired, series or parallel?
They are wired in series because the contacts are power-passing.
What is the formula to calculate sensible heat in Btu/h?
Qs = 1.08 x cfm x TD
What is the formula to calculate Watts?
Watts = Amps x Volts
How many Btus are in a watt?
3.413
What is the formula to calculate Btu/h?
Watts x 3.413
What is a fuseable link?
It works like an in-line fuse to protect the system from high amps or high temperature.
What causes hot spots on electric heat elements?
They are caused by a lack of air flow.
Why are contactors not used to start up electric heat furnaces?
They do not have capability to delay startup so all heat will start at one time, causing a large inrush of power. They are noisy because of the magnetic coil when they snap in. They may rattle or hum.
What is usually installed in ductwork that ensures the fan is blowing
A system switch or sailswitch.
Why is it better to use a sequencer than a contactor to turn on heat elements?
Contactors are noisy and do not have capability to space out the heating elements. They turn on all at the same time.
If you know the watts a heating element has and the voltage for the circuit, how can you figure out the individual fuse requirements for the element?
Take the number of watts for the element and divide by the voltage.
Example 7500W / 240V = 31.3A.
then multiple that figure by 125% and round up to the next figure
Example - 31.3A element x 125% = 39.1A which rounds up to 40A fuse.
Name six circumstances can cause a fuseable link or high limit switch to trip
1. Bad blower/motor/capacitor
2. Dirty filter/obstruction in return
3. Too many closed registers
4. Loose electrical connection
5. Undersized blower motor
6. Improper fuse size.
How are electric heating elements rated, in KW or BTUs?
In KW
Is the sail switch wired in series or parallel with the heat coil?
It is wired in series.
At what temperature are fuseable links set to?
They are set to melt at a temperature that is higher than the cutout temperature of the limit switch.
What is the table for wire gage and amps for first 500 feet?
6 - 50A
8 - 40A
10 - 30A
12 - 20A
14 - 15A
16 - 10A