How to change a 2-pin plug to 3-pin plug?

In Singapore, we use the 3-pin wall socket 240 V. In general, it is more convenient if the plug of appliance is 3-pin. But certain appliances we bought online may not be, just like the fan shown in the video below. It has 2 pins, i.e. a live wire and a neutral wire. No earth wire is present as the outer casing is made of electrical insulator, plastic.

Take a look at the video, and you can easily convert the 2=pin to 3-pin plug.

What if wires in the 3-pin plug are swapped?

Double-Insulated Appliance – Air purifier in the classroom

Double-insulated appliances are common around us. The air purifiers in our classroom are one good example.

In these appliances, only two wires are needed, namely Live and Neutral wires. Earth wire is not required as the casing is made of insulator like plastic for this case.

The classic air purifier in our classroom

The “double squares” symbol means that this appliance is double-insulated.

As you see, the earth wire is not required.

Why the fuse and switch must be on the live wire?

A common mistake is to state that the reason for switch to be on the live wire is “so that the switch can turn on/off the appliance”. This explanation is wrong.

Refer to the view for the reason why switch and fuse must be on the live wire.

In general, in the event where the fuse is blown or the switch is open, it disconnect the appliance from the high potential of the live wire. So the appliance will no become ‘live’ and it is save to touch even though there is a fault.

 

Why do we need earth wire and fuse?

Simply put, electric appliance can be very simple with just a live wire bring in the current and a neutral wire to bring the current out. The appliance can just work like this forever (without the hassle of having earth wire, fuse etc), provided there is no electric fault developed.

Both the earth wire and the fuse are safety features to protect the user and the appliance respectively. Take a look at the video below to understand the rationale.

Recall these notes given:

 

Click here for other related posts

double-insulation

3 pin-plug

 

Thick Cable for High Power Appliances

Double Insulation

Function of Earth Wire

What will cause the fuse to melt

Function of Fuse

The 3 pin plug

Functions Fuse and Earth Wire

SP N2007 P1 Q16 – Which events will cause the fuse to blow?

An electric cable contains three wires live, neutral and earth. The cable is correctly wired to a plug which contains a 3A fuse. The insulation becomes damaged and bare metal wires show.

Five possible events can occur.

• A person touches the earth wire.
• A person touches the neutral wire.
• A person touches the live wire.
• The live wire touches the neutral wire.
• The live wire touches the earth wire.

How many of these five events cause the fuse in the plug to blow?

A   1          B   2        C   3         D   4

Solutions: Option B

Consider the five events:

• A person touches the earth wire – As the person is at 0V, same as the earth wire, there will be no current flowing through the person. So current through the circuit will not be affected, which is lower than the 3A fuse rating. Fuse will not blow.
• A person touches the neutral wire.-  As the person is at 0V, same as the neutral wire, there will be no current flowing through the person. So current through the circuit will not be affected, which is lower than the 3A fuse rating. Fuse will not blow.
• A person touches the live wire. – The live wire is at high potential of 240 V. The person will get an electric shock. But a common misconception is that if a person gets an electric shock, the current flowing through him is very large, which is wrong. In fact, the current is very small, much smaller than the fuse rating. Assuming the average body resistance of the person is 100 000 ohms, and the potential difference in Singapore is 240 V, since I = V/R = 240/100 000 = 0.0024 A, which is lower than 3A fuse rating. Hence the fuse will not blow.
• The live wire touches the neutral wire. – This will create a short circuit as a large current which exceeds the fuse rating will from the live (240 V) to the neutral wire (0V) as that path has very low resistance. The fuse will blow.
• The live wire touches the earth wire. – This will create a short circuit as a large current which exceeds the fuse rating will from the live (240 V) to the earth wire (0V) as that path has very low resistance. The fuse will blow.

What’s the purpose of fuse and Earth wire, and how they work

How the wiring works and why fuse and switch must be on Live wire

Cost of Electrical Energy Consumption