Design documents
What is a Spanish Memoria Técnica de Diseño?
A Memoria Técnica de Diseño (MTD) is the REBT design document for a new installation, extension or alteration that does not fall into a category requiring a full project. It is prepared on the form set by the relevant regional authority.
Who may prepare and sign it
ITC-BT-04 allows the installation company authorised for that category or a competent degree-qualified professional to sign an MTD. This does not replace the installation company's role in construction, verification and issuing the CIE.
What an MTD is not
It is not a generic form that can be completed without inspecting or designing the installation. The calculations, diagram and protection must match the work. It also cannot be used where ITC-BT-04 requires a full project.
For the next part of the decision, see the guides to Project or MTD and When a project is required.
What information goes into a Spanish MTD?
An MTD needs the owner and site details, intended use, loads and power ratings, cable routes, conductor sizes and protective devices. A useful single-line diagram identifies each circuit and connects the paperwork to the actual distribution board. Cable length matters because a conductor with adequate current capacity can still have excessive voltage drop.
For an existing installation, the author must distinguish verified information from items requiring further inspection or testing. A photograph of the board cannot establish every concealed cable size or the condition of its insulation. Any additional circuit or different protective device must be reflected in the memorandum describing the installation ultimately verified.
In the Balearic Islands, the UDIT-001 procedure provides the MTD form and filing guidance. The right form makes submission easier but does not replace the engineering calculations. The MTD, CIE, drawings and declared power should be checked together before completing the file.
What an MTD author needs from you
A useful technical design report (Memoria Técnica de Diseño, MTD) describes an identifiable installation. Start with its address and use, planned power, any circuit diagram and previous paperwork. If boards, equipment or circuits have been added, the actual installation must be documented. The contracted power alone cannot reliably describe cables or protection.
An MTD is the design document for cases that do not require a full project. The electrical contractor subsequently tests the completed work and issues the CIE. Receiving a PDF called a 'technical report' therefore does not mean the installation has been registered or that the other Balearic commissioning steps have been completed.
How a useful MTD is prepared
- 01
Confirm that no ITC-BT-04.3 category requires a project.
- 02
List loads, powers, circuits and site conditions.
- 03
Size conductors and protection and check voltage drop.
- 04
Prepare the single-line diagram and route sketch.
- 05
Sign the MTD and coordinate it with the CIE and registration.
Frequently asked questions
Can only an electrician sign an MTD?
No. ITC-BT-04 permits either the appropriately authorised installation company or a competent degree-qualified professional.
Does an MTD replace the CIE?
No. The MTD describes the design; the CIE declares the completed installation and is signed through the installation company.
Regulatory basis and official sources
- Spanish Low Voltage Regulation (REBT) and technical instructions — BOE
- Balearic low-voltage installation registration (UDIT-001) — CAIB
Always check the current version of the rule and the administrative procedure that applies to the specific case.