AC Power Part 2: It's Rather Dark In Here

Now that you know how the power in your house works, let's look at what to do when it stops working.

Blown Fuses/Tripped Circuit Breakers

Probably the most common source of power loss the average Joe will see, this type of failure is almost always limited to a single circuit, or a group of electrical devices.

The cause of a blown fuse is frequently an overload - where someone attempts to draw more power that the circuit can handle.  The fuse burns itself out to protect the rest of the circuit.  Otherwise, this condition would present a major fire hazard.

To remedy a blown fuse:

A blown fuse.

1. Unplug or turn off all devices that lost power, if possible.  If you can, move some to outlets that still have power. The goal is to lessen the load on the fuse to a level it can handle.
2. Once that is done, determine which fuse is blown, and replace it.  Generally, fuses have an indicator that changes color (usually to black), or makes the broken internal filament clearly visible, to show that it needs replacement.  
3. Always replace a fuse with one of the exact same type and amperage rating.  Using a lower-rated fuse will cause repeated failures.  Using a higher-rated fuse brings us back to the fire hazard mentioned before.  
4. If the same circuit repeatedly blows fuses, even after reducing the number of items using it, that can be an indicator of a serious problem and needs to be addressed by a qualified electrician.

The remedy for a tripped circuit breaker is the same as a blown fuse: 

1. Reduce the load on the circuit, and reset the protection. A tripped breaker is easy to spot, as it will be in a central position between its "On" and "Off" setting, that it can only reach when it is tripped. 
2. To reset, move the handle fully to the off position, then return it to the on position.
3. As with fuses that blow repeatedly, a breaker that continues to trip needs to be addressed by a qualified electrician.

Tear-Outs and Downed Lines

A tear-out is when power lines are pulled from the ground, usually by excavating equipment.  There is an entire host of things that can cause downed power lines.

If you come across a tear-out or downed line, stay clear. Whether or not you can see it actively sparking, dangerous levels of power can still be present.  Call the local electrical utility or 911, and keep bystanders clear until professionals arrive.

This is a tear-out we had last week at work.  The location of the wire had been marked, but the equipment operator missed it.  Luckily, the operator was being careful enough that, while he destroyed the conduit, the wires were undamaged.  However, it took us a couple hours of testing and some specialized equipment to determine that everything was safe.  Had it not been safe, it could have been a very dangerous situation.  Being bad enough to make a professional adopt an extra level of caution should convey the level of hazard posed by this particular problem.

If you're doing any kind of serious digging, especially with equipment, please call all your local utilities and have them send out a locating crew, for everyone's safety.

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