What Is Meant By “Load” And “Supply” On A Switch?

Do you get confused by the terminology used in electrics? If electricity flows in a circuit, why isn’t it just called an electric circuit?

There are many terms used in electrics, and indeed they can be confusing to the public. Why is an electric circuit just not a circuit? Because the appliances you have in your home have a designated power requirement for the appliance to work. This is why you have different rated breakers in the consumer unit.


What is supply in an electrical circuit?

The supply is the power supply that is coming into your switch, ready to be used when the switch is on.

Once the switch is on, the supply power is converted into the circuit’s power load.

Don’t confuse this with the electricity generated and distributed across the country.

What is the load in the power supply?

Load is the portion of the supply used to power your appliance or light bulb. It’s the usable part of the electricity flowing through the circuit.

If you hear the term demand in a power supply, it is the same as the load.

What is the maximum load of a lighting circuit in a 3 bedroom house?

You will first need to know how many light fittings you have on the circuit. Your lighting circuit is likely to be a 6 amp ring final. It will be approximately 9 in a 3 bedroom house.

To calculate the demand, you must first refer to BS7671 and see what the British standard says about lighting circuits.

BS7671 states that a factor of 66% should be deducted from the overall load capacity for the home.


6A x 230 (incoming voltage) = 1380 W

9 bulbs x 20W (bulb watts that can vary) = 180 W ( which is a fraction of the available incoming wattage) 66% x 180 = 119 W for the whole lighting circuit 199 W/230volts = 0.5A

So, in essence, you have available 6A for your lighting circuit 9 x 20 w bulbs, 66% factor because it’s unlikely all of your bulbs will be switched on at any one time, which leaves 199W divided by the 230 volts to give 0.5 amps.

If you use downlights in your home, you might have 10 in the kitchen and 2 or 3 in the hallway, but the calculation remains the same.

BS7671 considered 100 W incandescent bulbs for their original equation but modern LED bulbs run at 5W, so the actual load requirement is significantly less than stated.

What happens if the load exceeds the RCD rating?

It’s a great question, and this is where load diversity comes into force. When you switch on an appliance such as a washing machine, it will only consume the full power load for two minutes.

As the washing machine cycles, it changes its requirements for the incoming portion of the electricity and switches to almost off when on a rinse cycle using very little load.

This is true for most appliances where the load diversifies, enabling the electrician to use smaller breakers while maintaining safety.

How is demand load calculated?

It’s a simple equation, and every electrician will have this equation stamped into his brain due to the amount of time it has been used.

The lighting demand factor = Demand interval factor diversity factor = (15 minute run time/ 15 minutes) x 10 = 1.0. Lighting demand load = 5 kW x 1.0 = 5kW.

What is meant by demand for electricity?

Power companies estimate the peak demand or the load needed by offices, domestic homes, offices, and commercial establishments such as shopping centres.

The records are historical and contemporary to keep up with demand.

This November, England’s first match in the World Cup will be against the USA. There will be a huge crowd across the UK, so electricity demand will be high, especially when people turn on the kettle to make tea at halftime.

However, more significant events affect peak demand, such as weather conditions.

What uses the most electricity in your home?

The main culprits for using the most electricity in your home will not come as a surprise to most of you:

  • Washing machines, particularly for young families.
  • Tumble dryer, almost always running at full load to heat the drum.
  • Dishwasher, the hot cycle heats the cold water to a high temp to provide gleaming plates and glasses.
  • The oven, depending on how much home cooking is done the oven draws a massive amount of electricity to heat up.
  • The fridge freezer always uses electricity silently in the background. Frost-free freezers are switching on and off constantly, using more electricity.
  • Heating and lighting can account for a whopping 27% of your yearly electricity bill.
  • Immersion heaters, when used, are the cause of high electricity bills.
  • Miscellaneous items such as computers and standby lights contribute to higher electricity bills.

What can you do to lower your electric bills?

  • Turn off lights when not in use, and install smart lighting systems.
  • Use natural light as much as possible throughout the day.
  • Use task lighting instead of illuminating the whole room.
  • Unplug used electronics. You don’t need to see the time on your microwave oven.
  • Ditch the desktop and use a laptop utilising battery power whenever possible.
  • Turn off unnecessary lights.

You can do so many things to trim down your electricity bill through the year, wash full loads instead of a couple of shirts or blouses.

How much does it cost to leave the TV on all day in the UK?

Using the figures from EcoCostsavings April 2022, the average TV in the UK uses 58.5 watts per annum, and in standby uses 1.3 watts. By switching your TV off when not using it, you would save £11.00 per annum.

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