CEI 64-8 in short
CEI 64-8 covers low-voltage installations within its scope. The ninth edition took effect on 1 November 2024. Sections 551 and 712 matter for off-grid solar, together with general protection, installation and testing rules.
A new edition does not automatically mean rebuilding an existing installation. The electrician must check its safety, the rules applicable when it was built and the requirements for changes or extensions. An unsafe condition must be corrected even in an older installation.
Island, alternative or parallel: three ways to power the house
- Island: the house takes energy only from panels, battery and possibly a generator.
- Alternative to the grid: the house takes energy either from the grid or from the system, never from both together.
- Parallel with the grid: system and grid work together.
A source working as an island must never be in parallel with the public grid. That is why an automatic transfer switch (ATS), two contactors with mechanical and electrical interlock, or a manual 1-0-2 changeover switch are used, disconnecting phase and neutral together. CEG diagrams
Solar PV: what section 712 asks
- gPV fuses: the need and rating depend on strings actually connected in parallel, possible reverse current, cables and the panel’s maximum fuse rating. String count alone is not enough. The CEG box described uses 16 A per string: check compatibility with Carmine and the installer.
- DC isolation: use a device rated for circuit voltage and current, including cold-weather voltage and pole layout. A breaker can isolate only if rated for that purpose. Check the CEG 32 A isolator for the actual circuit.
- Surge protection (SPD): type and voltage depend on lightning protection, cable layout and coordination. The box’s type 2 device is not a universal solution.
- Solar cables: H1Z2Z2-K, sized for current, temperature, installation method and voltage drop.
- Battery: coordinate BMS, isolation and DC protection with each branch. Do not assume built-in protection covers every cable layout.
Ask Carmine and your electrician. CEI 64-8 and off-grid
Inverters and earth faults
Fault protection must be checked in island mode and with grid or generator supply. An inverter may limit fault current, so do not assume the circuit breaker will trip. RCD type, sensitivity and position depend on the model, manuals and installation; A, F and B are not a simple quality ranking. The 300 mA type F RCD at the input in the CEG diagram does not replace required 30 mA protection on the relevant circuits. The electrician checks trip times, earthing and coordination in every mode.
Neutral and earth
On the CEG Growatt units he tested, Carmine reports readings of about 0 V between output neutral and the case. This is a test observation. It does not replace the manufacturer’s internal diagram or prove how the unit behaves in every mode, including bypass.
In the video, Carmine describes tests on some inverters with a floating output. Earthing the output depends on the model. Before any work, the electrician must check the manufacturer’s manual and test the protective devices. These tests are not a wiring plan for other inverters. N marks the terminal named neutral by the manufacturer; this alone does not authorise an earth connection. Ask Carmine or your electrician about your model. Video
Batteries: where and how
CEG LiFePO4 batteries do not need topping up. Follow the manufacturer’s instructions for periodic checks. Ask Carmine about any doubts or faults.
In Italy, electrical work serving buildings must be done by an authorised company under D.M. 37/2008, with a declaration of conformity and its attachments. A qualified professional designs the system when required; the company’s technical manager does so in the other cases allowed. The company checks filing duties. Building permits, site restrictions, tax duties and incentives depend on the case: check with the authorities and a tax adviser before work. No export to the grid does not remove all duties. For batteries and rooms, follow environmental protection, temperature, clearance and manufacturer requirements. Outdoor use is allowed only for suitable products. Use the proper collection route at end of life.
What about the «ARERA opinion 4140»?
A story is going around online about an «ARERA opinion 4140» that would make off-grid systems illegal. Carmine looked for it on the ARERA website and did not find it: in the video he explains why, in detail. Anyone can check for themselves on the ARERA website. For your system, the rules and the installer’s declaration of conformity still apply. Video
Who checks the system
In Italy, electrical work serving buildings must be done by an authorised company under D.M. 37/2008, with a declaration of conformity and its attachments. A qualified professional designs the system when required; the company’s technical manager does so in the other cases allowed. The company checks filing duties. Building permits, site restrictions, tax duties and incentives depend on the case: check with the authorities and a tax adviser before work. No export to the grid does not remove all duties. For batteries and rooms, follow environmental protection, temperature, clearance and manufacturer requirements. Outdoor use is allowed only for suitable products. Use the proper collection route at end of life.
FAQ
What is CEI 64-8?
CEI 64-8 covers low-voltage installations within its scope. The ninth edition took effect on 1 November 2024. Sections 551 and 712 matter for off-grid solar, together with general protection, installation and testing rules.
Does CEI 64-8 apply to off-grid too?
CEI 64-8 covers low-voltage installations within its scope. The ninth edition took effect on 1 November 2024. Sections 551 and 712 matter for off-grid solar, together with general protection, installation and testing rules.
Which sections concern solar PV?
CEI 64-8 covers low-voltage installations within its scope. The ninth edition took effect on 1 November 2024. Sections 551 and 712 matter for off-grid solar, together with general protection, installation and testing rules.
Which cables do the panels need?
Panels and strings: follow the model’s PV power, cold voltage, current and MPPT limits. SPF 6000 ES Plus has two MPPTs; total power alone does not give a universal limit per string.
Are surge protectors needed on the panel side?
- gPV fuses: the need and rating depend on strings actually connected in parallel, possible reverse current, cables and the panel’s maximum fuse rating. String count alone is not enough. The CEG box described uses 16 A per string: check compatibility with Carmine and the installer.
- DC isolation: use a device rated for circuit voltage and current, including cold-weather voltage and pole layout. A breaker can isolate only if rated for that purpose. Check the CEG 32 A isolator for the actual circuit.
- Surge protection (SPD): type and voltage depend on lightning protection, cable layout and coordination. The box’s type 2 device is not a universal solution.
- Solar cables: H1Z2Z2-K, sized for current, temperature, installation method and voltage drop.
- Battery: coordinate BMS, isolation and DC protection with each branch. Do not assume built-in protection covers every cable layout.
Ask Carmine and your electrician.
Does my existing system have to be redone?
A new edition does not automatically mean rebuilding an existing installation. The electrician must check its safety, the rules applicable when it was built and the requirements for changes or extensions. An unsafe condition must be corrected even in an older installation.