Homework 66 A
What is the function of a high limit switch on an electric heater?
A high limit switch senses the air temperature and opens the electrical circuit when overheating occurs.
When would the blower come on in an electric furnace?
The blower must come on before the first heating element and must remain on until the last heating element has been de-energized.
As a safety precaution, electric duct heaters should be wired so that they will not operate unless:
The fan is operating.
How warm is the supply air of an electric furnace compared to gas- or oil-fired furnaces?
Supply air temperatures for electric furnaces are lower.
How does an overload protection device on an electric heater differ from a fusible link?
The fusible link is a one time use that breaks and must be replaced. Overload/High limit resets when it cools.
Why are hydronic furnaces popular in geographical areas that do not require air conditioning?
This is because most residential air conditioning systems utilize air flow through ductwork that is not required for a hydronic heating system.
An advantage of a warm-air electric furnace compared to an oil or gas furnace is:
No vent pipes, chimney, or makeup air are required.
What power source does a electric heater normally operate on?
208 V to 240 V
What precaution should be taken when locating an electric baseboard heater near an electrical outlet?
Do not place the heater below an electrical receptacle.
What is an advantage of an electric baseboard heater?
Electric baseboard heaters can easily be installed in spaces where additional heating is required.
What protective devices do electric furnaces typically have?
Fusible links and thermal overloads in series with the heating elements
How are electric heating elements rated?
Electric heating elements are rated by their kW capacity.
What is a term used for a furnace that heats hot water which is then circulated for space heating by a circulation pump.
A hydronic type system or aqua system
Why is nickel chrome alloy used for electric furnace heating elements?
Nickel chrome alloy has a high electrical resistance and also resists oxidation.
What material are electric heater coils often made from?
Nickel-chrome alloy wire
What is the kilowatt rating of an electric furnace rated at 240 V and 30 A?
240 V × 30 A = 7,200 W, which is 7.2 kW
What happens to the current draw as an electric heating element warms up?
As the electric heating element temperature increases, its resistance also increases and the current draw decreases.
What are the requirements for replacement wiring in an electric furnace?
All replacement wiring used in an electric furnace must have a rating of 105°C (221°F) with an AWM type appliance wire rating.
When electric strip heat is used with a heat pump, when is the electric strip heat energized?
The heat pump comes on in the first stage, and the strips in the second stage.
When does the blower on an electric furnace operate?
The blower operates when the first heating element is energized.