Find out about the elements in your electrical installation
What is a main isolator (MI)?
The main isolator (MI) is a control element that disconnects the installation when the total power demanded by the appliances that are operating simultaneously exceeds the contracted power.
In accordance with current regulations (article 10 of R.D. 1454/2005) [PDF]) the installation of power control elements in dwellings is mandatory. Otherwise, a series of penalties will be added to your electricity bill (Additional Provision 2 of Order ITC/1559/2010) [PDF]).
Do you have an MI in your home's electrical installation?
If you do not have one, make sure you have a standardized box in which to place it. Otherwise, an authorized installer must install it.
If you so require, Iberdrola can help you with our Home Support service.
The main isolator is usually located alongside and just before the General Control and Security Panel.
This switch disconnects the entire installation when the sum of the power demanded by the devices in simultaneous operation exceeds the contracted power. If this occurs frequently, it indicates that insufficient power has been contracted.
This device protects the entire home installation from overloads and short-circuits. Because it has only recently come to form part of the General Control and Security Panels, many panels usually don't have one installed.
The RCD disconnects the electrical installation quickly whenever there is an earth leakage, thus protecting people from electric shocks.
These devices provide protection from the incidents caused by short-circuits and overloads in each of the interior circuits (lighting, heating, domestic appliances, etc.). The number of these SCBs will be equal to the number of circuits inside the dwelling.
In order to install the MI, a standardised box in which to place it must be available. The approximate size of the box is 15 x 20 x 9 cm.
Royal Decree 1454/2005, which amends certain provisions with regard to the electricity sector, and ITC Order 1559/2010 establish that electrical installations must be fitted with devices for controlling the demanded power.
This control of power in the case of domestic supplies with contracted power up to 15 kW shall be undertaken by installing a main isolator (MI) which is suitable for the contracted power.
Pursuant to Additional Provision 2 of the aforementioned Order ITC/1559/2010, a surcharge will be added to the contracted power you are billed for, with the application of a power to be billed of 10 or 20 kW, depending on the contracted power, for domestic supplies with a power up to 15 kW.
Prior to the installation of the MI, the electrical installation must be properly adapted, with a standardised box in which to house the MI.
In the event that said box is not present, you must contact an authorized installer, who will install it and leave it ready to house the MI.
Once you have the standardised box, you can either:
- Request that the distribution company install it on a rental basis (in accordance with the prices in effect at any given moment). Said company will install and seal the box during a single visit.
- Buy the MI on your own account and ask an authorized installer to install it. You must then contact the distribution company so that it can inspect and seal the MI.
As of the date of installation of the standardised box and/or the MI, you must inform the distribution company, which in accordance with current regulations will bill you in accordance with the rate and power corresponding to your supply (without penalty).
Based on the assumption that a standardised box in which to install the MI is present (otherwise, you must contact an authorized installer to perform the task), you have two options:
- Have the distribution company install it on a rental basis (MI monthly rental price: starting at ¤0.03, depending on the type of installation
- Install it yourself through an authorized installer. Subsequently, the distribution company will have to seal the installed MI.
In both cases, the distribution company will bill you ¤9.04 (without taxes) for inspecting and sealing the MI.
A possible consequence of the MI installation is that if insufficient power is contracted, the installation may disconnect when several appliances are used at the same time.
In this case, you will have to contract more power.
In order to contract more power than the maximum allowable for the installation (which is defined in the Electrical Installation Certificate, the former Electrical Report, for each dwelling), or if the installation is more than 20 years old, the distribution company will ask you to submit a new Installation Certificate.
If you extend the contracted power, you will have to pay the required extra for the access and extension fees for the increase in power:
- Extension Fee: ¤17.374714/kW (without taxes).
- Access Fee: ¤19.703137/kW (without taxes).
- Connection Fee: ¤9.044760 per connection (without taxes).
You should contact the distribution company in your area, so that it can install (where appropriate), inspect and seal the MI.
The telephone number of IBERDROLA DISTRIBUCIÓN ELÉCTRICA, S.A.U. is 900 171 171
If you want to find out about other distribution companies, check Distribution Companies.
The customers and supplier companies are entitled to request at any time that the corresponding body test the metering and control equipment installed, irrespective of their ownership. Verification costs and any amount owed are determined by the competent body.
If verification is requested by the customer and the metering and control equipment is found to operate properly, testing costs are borne by the customer. In all other cases they are borne by the company.
The demand meter's mission is to record the maximum power demanded by a customer during a 15-minute period, which will then be used to establish the power charge for the billing period. A demand meter can be incorporated into any meter. It is usually fitted on the active power meter of metering equipment.
Traditional needle demand meters are currently being replaced with integrated devices. The readings recorded by both the active power meter and the demand meter(s), the time-of-day rates, etc. can be read on the meter screen. With these integrated devices it is no longer necessary to use one meter for each type of energy usage and record the power, since they integrate several meters into one single device.
Billing with demand meter
This is quantified in two different ways based on the reading:
- If the power reading on the demand meter is less than 105% of the contracted power, 100% of that contracted power is billed.
- If the power reading on the demand meter is more than 105% of the contracted power, the power shown on the demand meter plus twice the difference between the power reading and 105% of the contracted power is billed.
It refers to the part of the installation that connects the distribution grid of a distribution company to the point of power delivery owned by the user, for both low voltage (LV) and medium voltage (MV).
As far as its construction is concerned, it can be underground or overhead, depending on the type of distribution (underground is becoming increasingly more widespread in urban areas).
This is an inspection and check of the regulatory conditions and technical features of a customer's installation before connecting to the main.
It is the process of connecting to power company installations and providing an electricity service.
Service connection fees refer to the financial consideration that must be paid to the distribution company for carrying out the actions that are required to provide a new power supply, or to extend an existing one.
Service connection fees can include the following items:
- Extension fees, which refer to the financial consideration to be paid to the distribution company by each user applying for a new power supply or for the extension of an existing one for the electrical infrastructure needed between the existing distribution grid and the first element owned by the applicant. For this purpose, an applicant means an individual or body corporate that applies for extension installations for the service connection, without necessarily having to contract the new supply or its extension.
- Access fees, which refer to the financial consideration to be paid by each user signing up for a new power supply or power extension for an existing one, which are paid for being connected to the grid.
- Charges for the supervision of assigned installations, which refer to the fees to be paid to the distribution company by the users applying for the new supply or for the extension of an existing one for the supervision of the work and tests and trials performed prior to service start-up, who opt for direct execution and subsequent transfer of the installations.
Distributors can charge for meeting the following service requirements:
- The connection: the operation of electrically connecting the receiver installation to the distribution company's network, which is liable for the carrying out of this operation.
- Verification of the installations: the inspection and checking that they meet the regulatory technical and safety conditions.
For those supplies in which the submission of an authorised electrician's report is required, either because it is a new installation or because some alteration work has been done, inspection charges will not be collected.
Neither will inspection charges apply if the submission of a project and the works' completion certificate have been required to execute an installation
Extension installations are those that are needed to provide a new supply or to extend an existing one from the existing installations.
Extension fees are paid by the applicants when they already know how much this item costs, before the service connection is made. Extension installations are those that are needed to provide a new supply or to extend an existing one from the existing installations.
Connection fees already paid are attached to the installations, houses, premises, plots, etc. for which they were paid, until the first user cancels them, however much time may have elapsed.
From a customer's cancellation date, the connection fees will remain attached to the installation for a further three years for low voltage power supplies.
On signing up for the supply for a home, premises, etc., the customer or end user will have to pay the corresponding access fees for the subscribed power to the distribution company, as long as it does not exceed the power recognised for the installation. If the customer or end user were to sign up for more power or extend the already subscribed power, he or she would also pay the required extra for the access and extension fees corresponding to the increase in power.
The installations of the new grid extension required to provide new supply or to extend existing supply of up to 100 kW of low voltage and 250 kW of high voltage, on developed land provided with the installations and services required by land development legislation prior to need for electrical power supply, defined according to Article 12.3 of the Spanish Legislative Royal Decree 2/2008 of 20th of June, by which the Revised Text is approved for the Land Law, shall be carried out by the distribution company of the area, giving rise to the application of the corresponding rights of extension, if and when these are not included within the corresponding investment plan. The modifications that arise as a result of the increases in power requested in a period under three years shall be considered cumulative as regards calculation of power and, in this event, shall be paid for by the applicant, taking into account the payments made for service connection rights during that period. The cost of the rest of the new extension installations required to meet the requests for new supply or extension of existing supply shall be paid for by the applicants, without requiring payment for the extension rights.
The maximum deadlines for a written response, counted in working days, for low voltage supply are as follows:
- When a transformer station is not required, 20 days.
- Definitive service with a medium voltage transformer station, 60 days.
- Definitive service with a medium to high voltage transformer station, 90 days.
Three months from the date of communication of the quote.
Depending on the type of works to be carried out they can be:
- Municipal permit for prospecting pits and conduits.
- Municipal permit for transformer station works.
- Third-party permits for building the designed installation.
- Approval from the supply company of the extension installation project to be carried out, as it must meet its officially approved regulations.
The deadlines, counted in terms of 10 workdays from the time of connection of the installation, once the service connection fees have been paid for low voltage power supply, are as follows:
- If a low voltage extension is not carried out: 10 days.
- If only a low voltage extension is required: 50 days.
- Third-party permits for building the designed installation.
- If a transformer station needs to be built: 90 days.
- If several transformer stations need to be built: 130 days.
It must be taken into account that these deadlines are automatically interrupted if difficulties arise, such as lack of permits, installation anomalies, work licences, etc., until these become available.
Electrical installation report
This is the low voltage "Electrical Installation Certificate", an official document issued by an electrical installation company and submitted to the competent body of the Autonomous Community in which it is installed to register it with the corresponding registry, expressly declaring that the installation was carried out according to the guidelines of the Low voltage electrotechnical regulation, approved by Royal Decree 842/2002, of 2 August and, if applicable, with the particular specifications approved for the Electrical company and, if applicable, with the Design Project or Technical Report.
The competent body of the Autonomous Community must complete 5 copies of the Installation Certificate, giving four copies back to the installation company, two for the company and two for the property, so that the owner can keep a copy and give another to the electrical company, which is a requirement that must be fulfilled before supplying the power to the installation. It shows the main characteristics of your installation, such as the installed power or the maximum power that can be supplied by the installation, and nothing can be contracted above that amount.
You will only need it when you carry out a new installation or you extend or update the existing one, and although you already have power, it's a good idea to give a copy of the Certificate to the distribution company for its records. The distribution company, which has a record of all the installation certificates from when the connection to the network was requested for the power supply, may request it when there is a substantial change to the conditions of the supply: change of the type of installation or power increase due to an extension of the installation or new installation.
Iberdrola can help you contact an electrical installation company through Mapfre MULTISERVICIOS, the leading company in refurbishment and repairs. Just call 902 136 532.
Iberdrola helps you keep your electrical installation safe
- If you are going to handle some part of the electrical installation in your home, you must first turn off the mains switch on the consumer unit.
- If you so require, Iberdrola can provide you with an authorised installer who will adapt the installation to your home. Send your request to the Iberdrola Home Support service.
- Electrical appliances must not be left within children's reach.
- All power sockets should have protective covers whenever they are not in use.
- Whenever possible, avoid having electrical appliances, cables, plugs, etc. in your child's bedroom.
- Take special care with radiators.
Bathroom and kitchen
- Bathrooms and kitchens carry a greater electrical risk as there is often steam or water vapour. Take special precautions in these rooms.
- Do not use electrical appliances near the shower or the bath.
- Never use electrical appliances with wet hands.
- Never use electrical appliances if you have bare feet.
- Do not use metal objects to remove a piece of toast stuck in the toaster.
- In the kitchen, do not use electrical appliances near the sink or in areas where there is steam.
- Switch off cooking or heating appliances before leaving home.
- Before cleaning a household appliance, unplug it.
- To unplug an appliance, do not pull the cable, pull the actual plug.
- Never put metal objects into an appliance which is in use.
What to do in case of electrocution
- Make sure the person is not in contact with any source of electricity.
- If the person is in contact with electricity, unplug the power source first and then the general supply, if necessary. Do not try to touch them or use any metal instruments.
- If they remain unconscious, try to resuscitate them if you know how to, or call 112 immediately.