Do I Need to Earth a Metal Back Box? YES & How To Do It

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Metal back boxes are found in every light switch in households; the metal back box is used for connecting the wires to front plate buttons and keys. Like any other metal conductor, it can conduct electricity, unlike the plastic back box, which can’t conduct electricity.

Do I Need to Earth a Metal Back Box?

Yes, you need to earth a metal back box; because the metal back box is considered bare-conductive metal and needs to be grounded, and this is due to the stripe made of metal connected to the socket’s back which links the fixing holes to the earth terminal and the metal back box via the 3.5 millimeters metal screw.

The metal back box can be either via a ground wire found in the socket wires or via ground screws. To determine whether you have ground screws, you need to search for a fixed lug on the metal back box side.

What Happens If the Metal Back Box isn’t Earthed?

When a ground fault happens while the metal back box is not earthed, anyone nearby the metal back box can get electrocuted. The grounding or earthing is responsible for the desperation of any power surge in the circuit to a safe place. Therefore, when the conductors are not the earth, the overcurrent or short circuit will try to find a shorter or alternative path; when someone touches the metal box, the current will flow through his body.

How to Earth a Metal Back Box?

  • Grab a wire
    You need to grab a bare copper wire; if the wire is insulated, you can use a wire stripper to strip the wire from the cover.
  • Connect the wire
    Connect the bare wire to the main box and attach it to the switch box using a small screw. The screw should have a green color; anything related to grounding should be green according to the electric color code. This can be useful in the future to let anyone know that the screw is for grounding.
  • Use grounding screws
    If the metal box doesn’t have a place to fit the ground wire, then you will need to use a bare metal screw and connect the wire to it, so any power surge is dispersed in the metal screw.

Is Metal Box Found In Both Metallic and Plastic Light Switches?

Yes, both metallic and light switches have metal back boxes, the plastic switches don’t have to be grounded, but their metal box has to be grounded; the ground wire is connected through the screw of the ground terminal in the back of the switch. The plastic part does not need to be earthed because the plastic is not a good conductor of electricity.

Meanwhile, the metal light switch has to be grounded; therefore, the grounding wire is connected to the switch and the metal back box. The metal is a good conductor of electricity, so if it is not grounded, it can cause electric shocks to users nearby in case of short circuit conditions or overcurrent.

Is it legal If You Don’t Ground a Metal Back Box?

Yes, it is legal not to ground a metal back box; however, some countries have other rules for not grounding it. Therefore, you need to check your local regulations; the inspectors recommend and insist on grounding the metal back box for every light switch, however, some households live safely without earthing the metal back box.

In some buildings, the grounding of metal back boxes is a must; for example, the government buildings or any building owned by the council can pass the electrical inspection unless all the light switches and metal back boxes are earthed. So if you are the house owner, it’s your call whether to ground the metal back box or not, but remember it’s highly recommended that you ground them for your safety.

What is The Back Box?

The back box is the part that is placed into the wall, and then the front socket is connected to it. The back box has two types, the plastic back box, and the metal back box, and each type is used for a specific wall type, for example, the plastic back box is used with stud walls, meanwhile, the metal back box is used for solid walls.

  • Plastic Back Box
    The plastic boxes are used for walls made of stud frames like wood, and then the plasterboards are used to finish the wall; this type of wall is known as stud partition walls. The plasterboard is cut to fit the plastic back box; the box is attached to the plaster through two lugs found on the sides of the back box; two screws are fitted into the lugs and then screwed into the plaster tighten the back box in place.
  • Metal Back Box
    The metal back boxes are used for hard walls, such as brick, stone, and breeze walls; a chisel is used to cut a place in the material of the wall for the metal back box to fit in. The lugs of the metal back box are fixed in place and can be either two or three lugs; screws are then used to tighten the back box in the wall through the lugs.

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How to Install a Metal Back Box?

  • Measure and Mark
    First, you need to mark and measure the back box position on the wall. You can use a marker and draw around the Box to mark the borders and exact measurements of the Box on the wall. After making the initial marks, remove the box and complete any missed marks using a ruler or a straight object. You should be careful when marking the back box position because there are minimum heights for installing a metal box; the box should be at a certain distance from units like the bathroom floors and kitchen floors.
  • Know the Depth
    You need to measure the depth of the metal back box before drilling into the wall to avoid drilling too deep, which can affect the stability of the metal back box. You know when to stop drilling by marking the masonry drill with electrical tape. Measure the depth of the metal back box and then measure the exact length of the masonry drill; start from the tip of the drill and mark the end by wrapping a piece of electrical tape around the drill.
  • Drill into the Wall
    After marking the depth on the drill, place the drill into the hammer drill and make sure it’s fitted, then use the chuck to tighten the drill in place. Choose any point on the lines you drew to start drilling, but the drill tip on the point, and start drilling until you reach the mark on the drill and then stop. Next, you need to repeat the process along the lines you drew; when drilling a new hole, try to make it close to the previous one as much as you can. In addition, you need to keep the drill on the internal side of the marked lines; try not to go out of the box you draw.
  • Clean with the Bolster
    After drilling along the marking, you can continue drilling inside the marking if you want, as it will make the job easier for you later; however, if you want to save time, you can use any 2 inches bolster chisel and a hammer to remove the remaining mortar, take the chisel and place its tip on the inside of the box, then start tapping using the hammer on the chisel to remove the remaining mortar. Don’t tap on the chisel too hard because you could remove big areas of mortar that will need to be repaired later.
  • Test the Metal Back Box
    After cleaning and preparing the slot for the metal back box, you can test if it fits properly and slide it into the hole; if the box fits well, you don’t need to remove any more mortar. If you face difficulties when trying to fit it in, you will need to use the chisel and the hammer again; when removing, take it slowly, and test the metal back box if it fits several times, so you don’t remove too much mortar.
  • Remove the Knockouts
    The metal back box would have knockouts on the bottom and top; you need to remove the knockout to fit the wires through the box, so if you know if the wires are going to be connected from the bottom, remove the bottom knockout. If the wire were connected to the box from the top, remove the top knockout.
  • Fix the Box in place
    You find two holes in the backbox; they are used to fix the box using two screws; therefore, you will need to remove the box if you fit into the hole. Then, grab two plugs and two screws; using the masonry drill, drill the holes in the wall after marking their location; you need to drill about 6-inches deep. Refit the back box into the cut again; screw the two screws to the plugs using a screwdriver.

How Deep Should You Cut in The Wall for a Back Box?

The depth depends on the size of the back box; not all back boxes require the same depth. If you are replacing an old back box with the same back box type, you shouldn’t change the depth unless you are changing the plate, when cutting in the wall, you should not cut too deep.

Start first with an approximate depth that equals the size of the back box; then, if you need more depth, you cut more because if you cut too deep into the wall, the back box will not be fitted properly.

Conclusion

To sum up, you need to earth a metal back box; the metal back box is considered bare-conductive metal and needs to be grounded because of the stripe made of metal connected to the socket’s back which links the fixing holes to the earth terminal and the metal back box via the 3.5 millimeters metal screw.

 The metal back box can be either via a ground wire found in the socket wires or via ground screws. To determine whether you have ground screws, you need to search for a fixed lug on the metal back box side.

The metal back box when not earthed and any fault happens the possibility of someone getting electrocuted. The grounding or earthing is responsible for the desperation of any power surge in the circuit to a safe place.

Therefore, when the conductors are not earthed, the overcurrent or short circuit will try to find a shorter or alternative path; when someone touches the metal box, the current will flow through his body.

Related Readings:

Where Does the Earth Go on a Plastic Light Switch? Answered

Do Socket Back Boxes Have to Be Earthed?

How to Identify Wires in a 3-Way Switch?

How To Identify a Traveler Wire in a Three-Way Switch?

How To Identify Switch Live Wire? Easy Thing!

What Color Wires Can Go Together? Complete Guide

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