How far you can run underground electric depends on the wire gauge (generally AWG) and the circuit voltage. Too much voltage drop in an electrical circuit can negatively affect performance, so the smaller the voltage drop, the better. Ideally, it shouldn't exceed 3%. The smaller the wire and the longer the run, the more significant the voltage drop. 

For example, with a 120-volt circuit, you can run 60 feet of 12 AWG cable without losing more than 3% voltage. With a 240-volt circuit, you can run 120 feet of 12 AWG wire while maintaining a voltage drop of 3% or less.

A light switch should be at least 2 inches from the edge of the trim of a door. The location of wall studs will often help determine where to put the light switch by your doorway, and in most cases, wall studs make it impossible to install the switch closer than 2 inches. When possible, try to keep the switch within arm’s length of the entryway.

The copper wire used in knob and tube wiring systems can last up to 100 years. However, it’s considered a dangerous and outdated wiring method because the cloth, fabric, or rubber insulation sheathing can become brittle and fall apart. Knob and tube wiring systems should be inspected if you’re considering buying a home with this type of wiring, or if you have problems with frequently tripping breakers, a sign that you may need to replace them.

You should never plug a normal 120v appliance into a special 240v outlet, as it can quickly burn out the appliance. This will cause irreparable damage to the appliance and, in worse case scenarios, cause damage to your circuit breaker. Check your appliance’s rating before plugging it into a 220v outlet to avoid electrical disaster.