Residential Electrical 101

Electricity can be difficult to understand, and a whole lot of people don’t understand it as well as they think they do.


Grounding is important, but not for the reasons most people think. Grounding your residential electrical system helps to limit voltage potential between the system and the earth, so in the event of a lightning strike, or other major line surge (such as a car hitting the telephone pole outside your house or the utility company opening and closing circuits), your house doesn’t go up in smoke. Grounding protects your house, and is just as important whether the power is on or off. Grounding a single circuit in a house is hardly worth the effort.

Grounding begins at the transformer, where the neutral (or grounded conductor) is connected to the earth. The neutral then travels to the house and is grounded again where it connects to the service panel. Newer electrical circuits also contain bare copper ground wires that connect back to that point. Since the wiring in your home is essentially a lightning antenna, the grounding system simply gives it a path to the soil. That’s all. Under normal circumstances, your computer will work just fine whether it’s plugged into a grounded receptacle or not.

If you really want to protect your sensitive electronics from power surges, have an electrician install a high quality surge suppressor in the main panel, and make sure your grounding system is intact and adequately sized. Then, you should plug your appliances into an uninterruptible power supply and a high quality surge suppressor. If the outlet is grounded, so much the better! Most important of all, don’t rest drinks near your laptop. My guess is root beer has damaged more computers than lightning has.

Voltage Drop

If you really want to protect your sensitive electronic equipment, you should probably be more concerned about something you may never have heard of, voltage drop. When current passes through a wire, it naturally meets some resistance, resulting in a small amount of lost voltage. This loss is called voltage drop.

Appliances draw a certain number of watts when they operate. Watts = Amps X Volts. When voltage drops, appliances draw more amps to compensate. The US National Electrical Code (which was adopted by Mexico as well) says that voltage drop should be kept below 5%, which is a bit unrealistic. Most electronic equipment is designed to run just fine with voltage drops between 5-10%. I’ve found voltage drops of around 10% in most of the homes I’ve inspected. In my opinion, voltage drop probably isn’t going to impact the vast majority of appliances until it gets to be 15-20% or higher.

Reversed Polarity

This is another very common defect we find in older as well as newer construction. In most receptacles, one of the vertical slots is a little shorter than the other. The shorter one should be “hot” and the longer one should be “neutral.” When the outlet is wired incorrectly so that the longer slot is “hot,” we call this reversed polarity.

Most appliances will operate just fine when plugged into a receptacle with reversed polarity, but it can be dangerous in certain circumstances. Since the solution (removing the receptacle and properly installing it) is simple and fast, we always recommend that they be fixed right away.

By: J. Morrison