Design documents
Electrical project or Memoria Técnica de Diseño in Spain?
Spain's REBT has two design-document routes: a full technical project for the cases listed in ITC-BT-04.3, and a Memoria Técnica de Diseño (MTD) for the remaining installations. The owner cannot choose the shorter document merely because it is cheaper.
The differences that determine the document
- A full project must be prepared and signed by a competent degree-qualified professional.
- An MTD may be signed by the authorised installation company for the relevant category or by a competent professional.
- Classification depends on use, type, design power and specific risk conditions.
- Where more than one category applies, the strictest criterion governs.
The practical difference
A project provides fuller design justification: calculations, drawings, single-line diagram, protection, conductor sizing and compliance. Work requiring a project is carried out under the direction of a competent professional.
The MTD records the main design data, basic calculations, connected equipment, diagram and route sketch on the regional authority's form.
The CIE is still required
The project or MTD describes the design. Once the work is complete, the installation company performs the verification and issues the CIE. These documents are complementary, not alternatives to one another.
For the next part of the decision, see the guides to When a project is required and MTD design report.
A practical example: project, MTD and CIE
Consider a small office and a bar with similar electrical demand. The office may qualify for a Technical Design Memorandum (Memoria Técnica de Diseño, MTD) if no other project trigger applies. A bar is classed as public-access premises under the Spanish rules and needs an electrical project even at low power. The actual use can therefore matter more than floor area or kilowatts.
The sequence explains the documents’ roles: a project or MTD sets out the design; the electrical contractor installs and verifies; the CIE certifies the completed installation. Where a project is mandatory, technical direction is also required. An independent initial inspection is added for the categories in ITC-BT-05. Commissioning one document does not automatically cover all these services.
When comparing quotations for Spanish electrical compliance, ask which professional handles each stage. A price for an MTD alone is not directly comparable with a complete service including measurements, remedial work, technical direction and coordination with the inspection body.
How to choose the design document before work begins
The useful question is which ITC-BT-04 category the installation falls into, rather than whether a full project seems more thorough than a technical design report (Memoria Técnica de Diseño, MTD). A dwelling, public-access premises and an industrial site may be classified differently even at similar power ratings. Use, specific hazards and the category's power threshold can change what is required. Choosing solely by floor area is unreliable.
Ask the professional to identify the regulatory category, planned power and whether the work is a new installation, extension or alteration. The CIE follows execution and testing; a design document does not replace it. Business-opening documents for premises in Menorca address a different procedure and should be coordinated before construction starts.
Frequently asked questions
Is an MTD simply a short project?
It is a shorter design route defined by the REBT, but it cannot replace a project where ITC-BT-04 requires one.
Can an engineer sign an MTD?
Yes. ITC-BT-04 allows a competent degree-qualified professional to sign it; the appropriately authorised installation company may also do so.
Regulatory basis and official sources
Always check the current version of the rule and the administrative procedure that applies to the specific case.