What are the most common homeowner electrical wiring mistakes?

Sunday, September 30, 2018

Do-it-yourself electrical work is always obvious to a home inspector, and not just because of code violations. An electrician does things in a neat, workmanlike manner that is immediately recognizable as professional. Unfortunately, sloppy amateur electrical wiring can be more than just embarrassing; both fire and electrocution can result.

   Here’s our top10 list of homeowner electrical blunders:

1) Open spliceThe primary purpose of the first electrical codes created at the beginning of the 20th century was fire protection. Fire was, and still is, the number one concern for electrical wiring. Because electrical fires most often start due to arcing or sparking at a loose wire connection, the code specifies than any wire connections be made in a fireproof box, such as an electric panel or smaller, receptacle box. Leaving the splice in the open, adjacent to flammable material, like in the photo at the top of the page, is a hazard. 

2) Ungrounded receptacle - Up until about 1960, home electrical outlets were 2-wire and had two slots on the faceplate at each plug-in point. Then the NEC (National Electric Code) was upgraded, and receptacles are now required to have a third, round slot for a ground connection. Without going into a long-winded explanation, the ground connection provides a route for any electricity that has gone astray in an appliance to flow to a safe location while tripping a circuit breaker, which warns that there is a problem in the circuit.
   Because running an additional wire to each pre-1960 receptacle is difficult-to-impossible for a do-it-yourselfer, many simply replace the old receptacles with new 3-slot ones—although the third slot is not connected to anything and creates a potential for electrical shock. The defect is easily detected with three-light plug tester. 

3) Reversed polarity receptacle - The black (hot) wire goes to the brass-color connection and the white (neutral) wire goes to the silver color connection. Getting it backwards to called reversed polarity and pros never get it wrong. This defect can also be recognized with a three-light tester.

4) Ceiling fan in a light box - Most bedroom ceilings 50-years ago had a simple light fixture at the center. But today a ceiling fan with a light kit under it is a popular bedroom enhancement. Unfortunately the electrical box that was originally installed in the ceiling was not designed to hold a 25 to 50-pound fan with light assembly below it. A stronger box with a cross-brace is necessary and an electrician can install one for you. Yes, fans do occasionally just drop out of the ceiling when installed in a lightweight box, but usually the assembly starts to come loose and slip down, giving a warning of the impending doom.


5) Unprotected electrical cable - Electrical cables in an occupied area of the home—where they could potentially be damaged—are required to be protected inside a wall or electrical conduit below eight feet from the floor. Securing the cable snugly to the wall is not acceptable alternative. Unprotected NM-cable to a kitchen disposal is a common defect in an older house. But, if the disposal is corded and connected to a receptacle, protection is not required.

6) Extension cord as permanent wiring - A permanent installation, such as a garage door opener, requires permanent wiring; which means an outlet within reach of the cord that came with the installed appliance. An extension cord is meant for temporary use and is not acceptable for delivering electricity to a garage door opener or wall air conditioner.

7) Wrong wire match at circuit breaker - Minimum wire sizes are specified for each circuit breaker amperage rating in an electric panel. If the wire size is too small, it will overheat and can start a fire before the breaker trips. Wire sizes get fatter as the numbers get lower. In copper wiring, a #14 wire is for a 15-amp breaker, #12 for 20-amp, #10 for 30-amp and so forth. So a #12 wire connected to a 30-amp breaker is a problem.
   While using a large wire than is specified for the breaker rating is not a defect in itself, sometimes it becomes one when a much larger wire is used and some of the strands have to be snipped to fit into the breaker connection. It’s called a “haircut” in the electrical trade, and is another safety no-no.

8) Double tapped circuit breaker - A few electric panels, mostly the ones manufactured by Square D and Cutler Hammer, are rated to accept two wires at their smaller amperage breakers. But most are not, and a double-tap is a common defect.

9) Missing NM-connector - An electric cable passing through a panel box needs a securing clamp, so that the connection at the breaker cannot be pulled loose inadvertently by a tug anywhere along the run of the cable. A homeowner will usually pop the largest knockout stamping in the panel box and run a couple of unsecured wires through it, like in the photo below.

10) Overpacked panel - Electric wiring generates heat and a crowded box is dangerous. If you have to push the wires in to close the deadfront cover, like we had to for the panel in the photo below, there will shortly be an overheating problem.

    The easy way to avoid all these common—and dangerous—defects in your home is to hire a licensed, professional electrician for the electrical part of your next home improvement project. 

    Also, see our blog posts What is the maximum number of circuit breakers allowed in an electric panel? and Can an electric panel be located in a bathroom? and Can a washer or dryer be located in front of an electric panel? and Can an electric panel be located in a closet? and Can an electric panel be mounted sideways-horizontally? and Can an electric panel be mounted over stairs?

• • • • • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:

Which house appliances need a dedicated electrical circuit?

Can a short circuit cause a high electric bill?

What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?

Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?

What causes copper wires to turn green or black in an electric panel?  

What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?

Why is it unsafe to bond neutral and ground wiring at subpanels?

Should I get a lightning rod system to protect my house?

Why is a strain relief clamp necessary for the cord connection to some electric appliances?  

Does a wire nut connection need to be wrapped with electrical tape?

What is the minimum clearance of overhead electric service drop wires above a house roof?

What are the requirements for NM-cables entering an electric panel box? 

What is the color code for NM cable (Romex®) sheathing?

Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

How can I find out the size of the electric service to a house?

Can old electrical wiring go bad inside a wall? 

What is an open electrical splice?

What are the most common electrical defects found in a home inspection? 

What is the life expectancy of electrical wiring in a house? 

What is an "open junction box"? 

How dangerous is old electrical wiring? 

What is a ground wire? 

I heard that aluminum wiring is bad. How do you check for aluminum wiring?  

What is "knob and tube" wiring?  

What is the code requirement for receptacle outlets in a closet?

   Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

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