Does a metal back box need to be earthed?

Asked By: Mane Rohwer | Last Updated: 4th May, 2020
Category: home and garden home appliances
3.9/5 (247 Views . 17 Votes)
A metal back box for a socket would be classed as an exposed-conductive part and as such it needs to be earthed. If the back box has a fixed lug on one side then the answer is that it will become earthed via the mounting screws as the socket front is attached to the back box.

Click to see full answer


Correspondingly, does a metal box have to be grounded?

The only requirement is that the application is grounded. Metal-sheathed wiring depends on bonding with the metal electrical box for grounding. Using metal-sheathed wiring with plastic electrical boxes, without taking other grounding measures, severs that ground and is highly dangerous.

Subsequently, question is, how do you ground a metal faceplate? For a metal face plate the earth should be connected to the face plate. The metal backbox is also required to be "earthed" by taking a wire from the earth slot in the face plate to the earth slot in the backbox. This is only required if both lugs (the threads in the backbox where the screw goes) are not fixed.

Also, do sockets need to be earthed?

Fixed wiring devices – including socket outlets – should not be wired with flex. An earth conductor insulated with green and yellow sleeving should be fitted between the earth terminal of the socket and the earth terminal of metal back boxes so that the metal box is earthed.

What happens if you do not connect the ground wire?

The appliance will operate normally without the ground wire because it is not a part of the conducting path which supplies electricity to the appliance. In the absence of the ground wire, shock hazard conditions will often not cause the breaker to trip unless the circuit has a ground fault interrupter in it.

37 Related Question Answers Found

How can you tell if a metal box is grounded?

Voltage measured between the hot terminal and the ground hole is a good indicator that the outlet and its electrical box are grounded. If you are dealing with a two-prong outlet, you can test for a ground at the cover plate screw before taking any steps to look inside the box.

Should I use plastic or metal electrical boxes?

Plastic boxes don't use metal cable clamps and do not provide the required grounding path. Metal electrical boxes are primarily used with metal-sheathed or "BX" wiring. However, they can also be used with Romex or NM wiring if desired. Most new residential electrical systems use Romex and plastic boxes.

Where does the ground wire go in a plastic box?

Because they are plastic, there is no need to attach a ground wire to it. Since it is made of a non-conductive material, switches and outlets cannot short out if they touch the side of the box. Plastic boxes usually come with tapped screw holes for easy attachment of switches and outlets.

What do you do with the ground wire in a junction box?

The junction box will have a green screw. Screw the ground wire to this as it connects to a tapped threaded hole on the back side of the junction box. If there's no screw, there should be a grounding clip. This secures the ground wire to the edge of the metal junction box.

Are metal switch plates safe?


For your safety, choose metal switch plates. They won't crack or break off exposing internal wiring. They are your most durable and reliable choice. Most cheap plastic plates discolor over time, so even buying the same brand and style will not guarantee a perfect match.

Can I attach ground wire to mounting screw?

Hook the screw loop around the green ground screw on your mounting bracket or light fixture and tighten the screw to hold it in place. If your light fixture has its own green ground wire you will need to connect the two ground wires using a wire nut.

What happens when there is no earthing?

Earthing. Without the earth wire, if a fault occurs and the live wire becomes loose, there is a danger that it will touch the case. The next person who uses the appliance could get electrocuted . As a result, the casing cannot give an electric shock, even if the wires inside become loose.

What happens if a house is not earthed?

If the house is not earthed, people could get electrocuted. Without an earth connection, the safety switches will not work and an electrical fault could cause a house or appliances to become 'live' as the current flows to earth. Earth stakes often do not work because: the earth stake is corroded or damaged.

Can I use 1.5 mm cable for sockets?

The cross sectional area of the earth wire in a 1.5mm cable is 1mm and in a 2.5mm cable it is 1.5mm. This should be sufficient for most domestic socket and lighting circuits.

What can you do with the earth wire?


Earthing is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault.

Is it safe to wire a plug without earth?

Some appliances will only have two wires - live & neutral. These are 'Double Insulated' and do not rely upon the earth wire for protection. The plug is wired as above but there is no earth wire to connect, however make sure that the screw on the earth terminal is not loose.

Why do sockets have two earth terminals?

The reason your sockets have two earth terminals, is so as to provide high integrity earth terminations for use in circuits where high earth leakage currents are expected. There's nothing to prevent you using such sockets for normal circuits, and just using one terminal.

Why is there no earth wire in Europe?

This was because on a room where there was earth in form of water or other earthed equipment it was not safe to use an unearthed equipment. A fault could cause a shock between live wire and earth which could be fatal. Schuko plug and socket: The wires also have two layers of insulation.

Why do you need an earth wire in a plug?

Thus the earth wire helps protect you if you touch the case of an appliance that is "live". The earth pin on a plug is longer than the line and neutral pins. This ensures that the earth pin always connects with the socket first.

Why do some electrical appliances not have an earth wire?


Double insulation. Some appliances - such as vacuum cleaners and electric drills - do not have an earth wire. This is because they have plastic casings, or they have been designed so that the live wire cannot touch the casing. As a result, the casing cannot give an electric shock, even if the wires inside become loose.

Do you need to earth a plastic back box?

This MK back box does not have an earth terminal (according to the Q&As at the link below). The Q&As state the box is plastic, so doesn't require an earth, but has the capability to add an earth terminal if required.

How do you plug a socket into the earth?

An earth conductor insulated with green and yellow sleeving should be fitted between the earth terminal of the socket and the earth terminal of metal back boxes so that the metal box is earthed. Screw holding the faceplate to the metal backbox are not a reliable means of earthing the box.