Week 4 Unit 67 HW Review Questions

Why should furnaces not rest directly on the ceiling joists?

• Turn your ceiling into a drum

• The ceiling will act as a sounding board and transmit the blower sound throughout the house.

• bzzzzzzzz

How is fiber duct connected to the furnace?

• Duct butter

• A 3" metal collar is fastened to the flanges on the unit with sheet metal screws. The duct board is connected to the collar using long screws with large 2½” square washers. The joint will then be sealed.

• Pookie

• Put some tape on it

How is the power wire sized for an electric furnace?

• Pick your favorite color

• small wires are easier to get through a hole

• The power wire should be sized to handle at least the minimum circuit ampacity on the data plate.

What is necessary to make a safe connection with aluminum wire?

• The connectors must be rated for aluminum wire and the wire should be coated with ant-oxidation paste.

• don't put it to your lips

• plug it all the way in

An electric furnace has a minimum circuit ampacity rating of 50 amps. What is the minimum current rating for the disconnect switch?

• 50 amps X 1.15 = 57.5amps

• Pg. 1245 115%

Where should the disconnect switch for the furnace be located?

• On top the side of the condenser

• Within sight of the furnace and in accordance with local codes.

• In garage or attic

How is the overcurrent protection sized for and electric furnace?

• By starting at the largest breaker so it will not trip

• Must match your fuse in the fuse box

• The over current protection should be no larger than the maximum over current protection listed on the unit data plate.

Discuss the effect of reduced voltage on electric furnace capacity.

• Reduced voltage lowers the furnace capacity. A furnace operating on 208 volts instead of 240 volts will have only 75% of its rating at 240 volts.

• We need more power

Discuss the operational checks that should be made on a new electric furnace installation.

• Make sure the wires are tight and fire it up

• The voltage to the furnace should be checked both before and after starting the unit to check for voltage drop. The voltage and current draw of each strip should also be checked. The temperature rise should be checked and the airflow adjusted if necessary.

Draw a connection diagram for the 24-volt controls on an electric furnace.

• DRAW

• Drawing is fun