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Monday, 7 May 2012

What's the point of 110V?

110V appliances are often used on construction sites. 110V transformers are used to produce 110V from the UK mains voltage of 230V. What's the benefit of using 110V?

The main reason for using 110V transformers and 110V appliances are to reduce the risk of a user getting an electric shock. In order to understand how 110V transformers help, we first need to understand some background information about Voltage, Current, resistance of the human body and electric shock.

Voltage is simply electric pressure. Just like water under high pressure will result in a higher volume of water flowing, a higher voltage exterts a higher electric pressure in circuits.

230V mains voltage exterts twice as much pressure as 110V. However when a 110V transfomer is used to generate 110V from 230V mains, a centre tapped transformer is used. What this means is that the transformer actually produces 55V on either side of earth to produce 110V when the two are added up. This means that the maximum voltage with respect to ground is only 55V. So, when a 110V transformer is used, the electric pressure is a quarter of what it is when compared to mains voltage.

Well, how does this help to reduce the risk of electric shock?

Electric shock is a result of a currrent flowing through a body to ground. The current that flows with an electric pressure of 230V is 4 times higher than with an electric pressure of 55V.

What level of current is dangerous?

Well, no two human beings are alike but the following is a general indication of what the effect of different currents are on the human body.

1 to 2 milli Amps                         Cannot normally be felt
5 to 10 milli Amps                       Painful sensation
10 to 15 milli Amps                     Muscular contraction
20 to 30 milli Amps                     Impaired breathing
Greater than 50 milli Amps          Ventricular fibrillation

What determines the level of current flowing?

The level of current depends on two things. One is the electric pressure, which is the voltage present. The other is the resistance of a human body. This can vary enormously depending on whether the hand touching the voltage is wet or dry and is clasping a live cable or just touching it with the back of the hand. 

Appliances being used outside, such as on a contstruction site is more likely to be wet and is more likely to result in a higher current and more chance of causing serious injury.

How a 110V transformer helps reduce injury from electric shocks.

The use of 110V transformers help by reducing the electric pressure by a factor of 4. For example, if the resistance of a human body is such that a current of around 25 milli Amp would flow if the voltage was 230V, then with a 110V transformer in use, with everything else being equal, only a current of around 6 milli Amp would flow.

This will make the difference between Inpaired breathing and just a painful sensation, when a 110V transformer is being used.


Using 110V transformers can reduce the current from an electric shock by a factor of 4 and reduce the injury caused.

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