Better Safe Than Sorry

In this episode - Better Safe Than Sorry . . .

Can you identify the device in the photo? Here's a clue: it's the size of your thumbnail and functions as a safety device that shields an electrical circuit from excessive current flow. Often found in modern-day furnaces, this device is a 3-amp fuse. Fuses are essential components in electrical systems to protect equipment and wiring from overcurrent conditions that can cause electrical fires or damage other electrical components.

We recently had our home repainted and had to remove all the light fixtures, electrical outlet covers, heater grates, and the thermostat that manages our HVAC system. An electrician advised me that it's important to unplug your furnace from its electrical outlet, cover exposed wires with electrical tape or wire nuts, or shut down the power from the circuit breaker panel box before starting any electrical work. Why? Because the thermostat, connected to the furnace, is powered by a DC transformer that is commonly damaged if not protected by a fuse. The "3" on this fuse indicates its current rating. This means the fuse will allow up to three amperes (or three amps) of electrical current to flow without blowing or "tripping" a circuit. If the current exceeds three amps due to a short circuit (wires touching) or some other fault in the circuit, the fuse will heat up and melt, breaking the circuit and cutting off the flow of electricity. This action protects the connected devices and prevents potential damage or fire.

Fuses are available in various sizes and current ratings, the appropriate rating depends on the specific electrical circuit and the devices connected. Using a fuse with too high a current rating for a circuit can lead to inadequate protection while using one with too low a rating can result in frequent, unnecessary fuse blows. Selecting the right fuse for a given application is essential to ensure safety and proper circuit protection.

A qualified electrician would easily recognize this particular fuse. However, you might need help to identify this one if you have never seen the various shapes, sizes, and capabilities of different fuses. 

Historically, (1950s & 60s) fuse panels had round fuses roughly the size of a quarter. They had a glass window that allowed you to see if the fuse was blown and the connection severed. In the movie Christmas Vacation, a modern breaker box with built-in circuit breakers acted as fuses to protect the circuits.

Also, if you have ever browsed Home Depot's electrical department, you may have seen fuses that looked like large lipstick tubes with copper ends.

Once the painting project was finished we reconnected the Nest Thermostat to its backplate, an error message appeared, "No power to the unit." We tested the power wire using an AC voltage meter, but that didn't work. You see, the thermostat operates from a DC transformer, which can easily burn out without proper protection from a fuse. Your doorbell may also use a DC transformer - on a different circuit.

When asked to check if the furnace fuse was blown, I realized I had no idea what to look for. If you are facing a similar problem, check the fuse first. Remember, electricity can be dangerous, and it's always best to call a qualified electrician if you have any doubts.

My friends, it's better to be safe than sorry.

I'm Patrick Ball; thanks for listening. See you in the next episode.