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What the simultaneity factor is and how this is calculated

Switching on every electrical appliance in your home puts your electrical power to the test. This is what the simultaneity factor means and why it matters to you: because whether you can carry out your routine without your electricity tripping depends on this.

Your home's electrical power is something that matters to you. If you are unclear about this, here are two compelling arguments:

1. It matters to you because it costs you money: approximately half your bill. This is a fixed cost you will pay every month and it will be greater the higher your contracted power.

2. It matters to you because it makes life easier: the more power, the more electrical appliances you can switch on at the same time. If your power falls well short, this can complicate your routine to the point that your electricity cuts out if you switch on the washing machine while using the hoover, for example.

In balance lies virtue: you need electrical power that enables you to live your life while paying as little as possible.


What is the simultaneity factor?

The simultaneity factor is a simpler formula than it appears. You have to take these two aspects:

1. The maximum power tolerated by your electrical installation.

2. The sum of the power required by all of the devices connected to your electric installation.

The simultaneity factor is the result of dividing the first by the second.

1. The maximum power of your home appears in your electricity report or Electrical Installation Certificate (EIC). You cannot contract more power unless you call a specialist to inspect your installation and issue a new electrical report that certifies that it is safe to increase the maximum power (this may involve replacing the cabling or even your home's electrical panel).

2. The sum of your devices' power is calculated from the amount of kW required by your washing machine, microwave, extractor hood, television, computer, hair dryer, dishwasher, induction hob, etc. Essentially every single device that requires electricity to work.

“The simultaneity factor serves to calculate how much electrical power your home will need.”

Why the simultaneity factor matters to you?

If you think that such technical terms don't matter to you, think again. In reality, your home's simultaneity factor matters to you more than anyone else. It obviously doesn't matter to your neighbour if you can't use the oven and dishwasher at the same time.

When calculating the simultaneity factor, a very important aspect is taken into consideration: all of your home's devices will never operate at the same time. Some of them will, others won't. For example: it's reasonable for your fridge, television and washing machine to be on at the same time, but not for your air conditioning and electric heating to be on at the same time.

The simultaneity coefficient serves to correct this. This adjusts the simultaneity factor according to experience by processing various information:

  • Use of the installation in the past.
  • References from similar installations.
  • Legal indications.

How is the simultaneity factor calculated?

Let's get practical: how does this all apply to you specifically?

You need to calculate your maximum simultaneous power, i.e. the maximum power required from your electrical installation under normal circumstances.

These are the steps to follow:

1. Add up the power required by your electrical appliances: this data can be found in the device's instruction manual and is usually on a technical specification label stuck somewhere on the device.

If you don't want to check every single device, don't worry. Focus on your main electrical appliances. Contracted power is shown on your bill and contract in kW. It is likely the specifications of some devices will be shown in W. To convert from W to kW, just divide by 1000.

For a general idea and to make sure that you're on the right track, the usual power required by the following electrical appliances is shown below. Bear in mind that these figures are very approximate and vary quite significantly depending on the age and energy efficiency of the electrical appliance:

  • Television: 100-400 W (0,1-0,4 kW).
  • Air conditioning: 900-2.000 W (0,9-2 kW).
  • Microwave: 900-1.500 W (0,9-1,5 kW).
  • Fridge: 200-400 W (0,2-0,4 kW).
  • Oven: 1.200-3.000 W (1,2-3 kW).
  • Incandescent bulb: 30-80 W (0,03-0,08 kW).
  • LED light bulb: 3-12 W (0,003-0,012 kW).

2. Correct the result with your own simultaneity coefficient: you have to reduce the result based on your own daily use, which you know better than anyone. Here is some basic advice:

The sum cannot include both air conditioning and electrical heating: remove whichever device requires less power from the final result.

Multiply the total sum of all the light bulbs combined by 0.66: this is a simultaneity coefficient commonly used for domestic lighting.

Your routine calls the shots: will you need to use the hoover at the same time as the washing machine? Do you wash dishes at the same time as using the oven? You decide what you do and don't want to assume.

3. Compare the corrected result with your contracted power: ideally, the result you obtain will be close to your contracted power (kW). If your result differs significantly from your contracted power, it means you have excess power and you could save quite a lot on your bill:

Other uses of the simultaneity factor

The simultaneity factor is also widely used by architects, engineers, developers and electricians. They use it to calculate the electrification of a building and the electricity report (EIC) for each home, premises and garage.

There are three power scores: high, medium and low. Power is greater in the high category, because it is understood there will be more electrical consumers in operation simultaneously. For low, the opposite is true, with fewer electrical consumers. According to these ranges and other variables (such as the simultaneity factor) the developer and electrician draw up individual EICs, as well as the overall EIC for the entire building, to request the necessary power from the distribution company.


Electric cars and the simultaneity factor

Today, we are witnessing a prolific exchange of news and opinions on electric cars. One of drivers' main concerns is how to charge an electric car, especially in private car parks, as these facilities are generally not geared up to charge several cars simultaneously.

In this regard, it's worth highlighting that the speed at which cars charge determines the necessary power and time. That is, there will be systems and batteries that can charge a vehicle in a couple of hours, which uses a lot of power. Logically, if there are several vehicles on charge in the same garage at the same time, the power control switch will most likely trip. If they are not charging simultaneously, there won't be a problem.

Similarly, if the charging period is longer, less power will be required, so charging several electric cars simultaneously would not be a problem either.

As such, optimising batteries and charging systems will be a key factor in not having to revise, among other issues, the simultaneity factor, which will modify the power contracted from the service provider or will mean that facilities will need to be altered in car parks or homes. It is possible that, in the future, administrations, distributors, builders and contractors will have to modify their processes for new projects to take electric cars and the simultaneity factor into account.

“The simultaneity factor plays a crucial role in building homes, as well as in the future of the electric car in our cities.”
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