What is an arc-fault circuit interrupter (AFCI) designed to do?
- Detect small leakage currents that could shock a person
- Limit the voltage delivered to sensitive electronics
- Detect arcing in wiring and shut the circuit off
- Switch the house to backup power during an outage
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C. Detect arcing in wiring and shut the circuit off
An AFCI recognises the electrical signature of arcing, such as at a damaged cable or loose connection, and opens the circuit before it starts a fire. Detecting leakage current to protect people is what a GFCI does.
Reference: Electrical: AFCI operating principle (NEC 2023 210.12, concept)
What is the basic difference between a boiler and a furnace?
- A boiler heats water; a furnace heats air
- A boiler burns oil only; a furnace burns gas only
- A boiler heats one room; a furnace heats the house
- A boiler needs no venting; a furnace needs a chimney
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A. A boiler heats water; a furnace heats air
A furnace warms air that is distributed through ducts, while a boiler heats water (or produces steam) that is piped to radiators, baseboards or radiant tubing. Either can burn gas or oil, and fuel-fired units of both kinds need venting.
Reference: Heating: system types
In a cold climate, on which side of the wall insulation is a vapour retarder normally placed?
- The warm-in-winter side, toward the heated room
- Both faces of the insulation, sealing it in
- The cold-in-winter side, against the sheathing
- The middle of the cavity, between two batts
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A. The warm-in-winter side, toward the heated room
Water vapour moves from the warm, humid interior toward the cold exterior. Placing the retarder on the warm side keeps vapour from reaching cold surfaces where it would condense. A retarder on both sides can trap moisture in the cavity.
Reference: IRC 2021 R702.7 (vapour retarders, concept)