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What are maximeters and what are they for?

When power is used above the limits of your electrical installation, the fuse blows and you are left with no electricity. This does not happen where a maximeter is installed, since this device enables the power limit to be exceeded. What is the purpose of this exception?

In most homes and electrical installations, the electrical panel is regulated by the PCS. The Power Control Switch (PCS) is not very smart but knows what it's doing: if you exceed your power limit (or if it detects a short circuit), the electricity cuts off.

When this happens (when the fuse blows, as they used to say), it needn't be a problem. Resetting the meter to get your electricity back  is a quick and simple procedure.

But why did the PCS do this to you? Essentially, for your safety. Your home has a contracted power limit that marks the number of kWs that can be used at the same time. So, if you turn on more and more appliances (washing machine + electric over + air conditioning + vacuum cleaner, etc.) the kWs accumulate and reach a point when the PCS blows. 

If you have issues with this kW limit (because you think it is too high or too low), you should check whether your contracted power is adequate for your home.

However, in some electrical installations, there is no PCS. Instead, there is a maximeter, a device that enables the power limit to be exceeded.

“A maximeter enables the electrical power limit to be exceeded without cutting off electricity.”

How do maximeters work?

In an installation with a maximeter, more power than that contracted for can be demanded. You can exceed the limit but the electricity will not be cut off.

A maximeter works as follows: it takes note of the power being demanded and does so in 15-minute blocks. For each of these blocks, it calculates the average power required in that specific period of time. At the end of the month, it remembers the maximum power limit requested and records it.

However, although the supply is never cut off, exceeding the power limit will affect your electricity bill. 

Power is measured in kW and there is a price in euros per kW. Maximeters typically work with the following formula and in 3 possible situations:

  • The maximum power is less than 85% of the contracted power: throughout the month, the peak power has not reached 85% of the power that features in the contract. In these cases, 85% of the contracted power is billed.
  • The maximum power is between 85% and 105% of the contracted power: the peak power for the month is around the same value as the contracted power and, therefore, the exact contracted power is billed.
  • The maximum power exceeds 105% of the contracted power: during the month, there has been excess power that needs to be paid for. This formula is applied: 105% of the contracted power is subtracted from the maximum power peak. The result is the power to be billed.

“A maximeter is only installed in homes inhabited by patients with certain medical treatments (assisted breathing, dialysis, etc.).”

Why do we have maximeters?

The normal situation is the following:

  • High voltage or power levels exceeding 15 kW: these installations have a maximeter.
  • Low voltage or power levels lower than 15 kW: these installations have a Power Control Switch (PCS).

This is because it is in high voltage or high power-level installations that the type of installation (industries, factories, etc.) requires flexibility in terms of the excess power level. Meanwhile, installations with a low voltage or a power-level lower than 15 kW are mostly homes in which safety prevails over the non-interruption of supply.

However, there are exceptions to this rule. There are low voltage installations or those with power-levels lower than 15 kW in which the electricity supply can never be interrupted, not even for a few minutes. For example:

  • Lifts.
  • Hospitals, especially operating theatres and intensive care units.
  • Homes with special medical circumstances: people who need assisted breathing or dialysis.  

If you are in any of these situations, we explain how you can ask to have your PCS replaced by a maximeter:

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