In many YouTube videos showing how to safely complete electrical projects in your home you will see people like Scott of Everyday Home Repair use plastic electrical boxes for outlets and switches. In some jurisdictions it is more common or even required to use metal electrical boxes. You may also run into a metal electrical box in your home that was installed before plastic boxes became more common.
There are some important differences between a plastic box and a metal box. If you are just starting to work with metal electrical boxes, here are five mistakes you need to avoid.
Mistake 1: Not securing the Romex cable in the box
A plastic box has a tab inside the hole that you push the Romex through and this tab holds the cable by tension. In a metal electrical box you decide which of the four holes you want to use to run the cable into the box based on which direction the cable is coming to the box.
You start by removing the cover from that hole. It is usually easiest to pry it up with a square head screwdriver and then twist it off with pliers (I recommend the Milwaukee 6-in-1 electrician pliers). After you push the cable into the box, you need to tighten the plate that holds it in place using a number 2 square screwdriver. The plate pushes the cable against the back of the box securing it. Tighten it all the way so the cable doesn’t move.
These plates come unscrewed so it is easier to insert the cable. If you are not using one of the ends of the box for cables, make sure to tighten that plate all the way to the back so it is out of the way.
Mistake 2: Not grounding the box
A plastic box does not conduct electricity so it does not need to be grounded. This is why you often see in videos the ground wire connected directly to the outlet or switch. But a metal box can conduct electricity and it can be dangerous if a hot wire or terminal screw touches the side of an ungrounded box.
Always connect the ground wire from each cable to the grounding screws at the back of the box. There is a slot that the wire fits into so it will be below the screw. I often use needle nose pliers to guide the ground wire under the screw and make sure it is in the slot. Tighten the ground screw all the way so the wire does not move. By grounding all wires to the box you are keeping the ground connection complete.
Mistake 3: Putting the ground wires in the wrong direction under the screw
When the ground wires are in the wrong direction, it increases the chance that the wire can come out from under the screw when it is turned and leave the box unprotected. The screw turns clockwise so a wire coming in from the bottom should go on the left side of the screw and a wire coming in from the top of the box should go on the right side of the screw. This way when the screw gets tightened it pulls the wires in under the screw instead of pushing them out.
Mistake 4: Putting multiple wires under one side of the screw
If you have a lot of wires that go through the box you may have too many wires to put each wire under one side of a screw. Don’t put two wires under one side of the screw and one wire on the other side. The slots beside the screws are not meant for more than one wire so they won’t help hold two wires in place properly. The screw cannot properly tighten when one side is lower than the other side, leaving a possibility of a dangerous missed ground connection.
If you have for example five ground wires that need to be connected, you will need to use a pigtail. Connect one wire and the pigtail under one of the grounding screws. Then connect the pigtail and the other ground wires using a five slot Wago connector.
If you are not familiar with Wago connectors, Scott is the one who I first heard about them from. They are a great solution especially when you are dealing with multiple wires. They come in two, three, or five slot versions as well as a straight through connector version. You can get a multi-pack from Amazon using this link.
Mistake 5: Not leaving enough ground wire after connecting it to the box
After you connect the ground wire to the box, you still need the wire to come out and connect to an outlet, dimmer, or smart switch. If you are just installing a simple light switch you may be tempted to do what many electricians did in the past and cut the ground wire just past the grounding screw. A simple light switch doesn’t require a ground wire so they clean up the box by cutting the ground wire.
The problem comes when you need that ground wire to install a dimmer or smart switch. If you run into this situation, you can add a pigtail to an open side of a grounding screw so that the dimmer or smart switch can be connected to the ground. Make sure the short original ground wire doesn’t slip out when installing the pigtail.
Video of these five mistakes and how to correct them
If you prefer to see how to avoid these five mistakes in video format, click the image below to watch my YouTube video where I explain and demonstrate these five mistakes.
If you want to safely complete electrical projects at your home and it is legal to do so in your jurisdiction, I recommend the videos that Scott at Everyday Home Repair has produced. His playlist of videos is here.