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CEG diagrams

Interlocked contactors: the alternative to the ATS

Two contactors, an interlock and a relay do the same job as an ATS with standard panel components. Here is how the CEG diagram works.

Block diagram of a system with two contactors and mechanical interlock
CEG block diagram: system with interlocked contactors. Click to enlarge.

1. The idea

One contactor connects the house to the Growatt, the other connects it to the grid. They must never be closed together, otherwise grid and inverter would be in parallel. That is why they have a double interlock.

2. The double interlock

  • Mechanical: a physical block fitted between the two contactors prevents both from closing.
  • Electrical: a normally closed (NC) auxiliary contact of each contactor is wired in series with the coil of the other. If one is closed, the other cannot receive the command.

3. Priority to the Growatt

Relay KA has its coil powered by the Growatt line. As long as the Growatt supplies voltage, KA keeps the grid contactor's command open and the house stays on the system. If the Growatt stops, KA releases and the grid contactor connects the grid to the house. So the house stays on solar whenever possible and uses the grid only when needed.

4. Components in the CEG diagram

  • 2 contactors 40 A AC-1 (63 A for the 12 kW system), with mechanical interlock.
  • 2 auxiliary contacts 1NC for the electrical interlock.
  • Relay KA.
  • 2 fuse holders with 3 A 230 V fuses for the coils.
  • Towards the house: T1+T2 surge protector and 2P 32 A breaker.

Materials

5. Mistakes to avoid

  • Fitting only the mechanical interlock, or only the electrical one.
  • Contactors that only break the live: they must break live and neutral.
  • Coils without protection fuses.

6. The detailed wiring diagram

The block diagram helps you understand how it works. The detailed wiring diagram, with terminals and connections, is reserved for those who bought through Carmine Energia Gratis: write to Carmine with your CEG pre-order number. Wiring and testing must be done by a qualified electrician.

Ask for the detailed diagram All CEG diagrams

7. Frequently asked questions

ATS or contactors: which is better?

They do the same thing. Contactors are standard panel parts, easy to find and replace; the ATS is a single ready-made device. The choice depends on the panel and on your electrician.

Why two interlocks instead of one?

For safety: if one fails, the other still prevents grid and inverter from going in parallel.

What is relay KA for?

It gives priority to the Growatt: while the Growatt is on, the house stays on the system. When it stops, the command passes to the grid.

Which contactors for 12 kW?

In the 12 kW CEG diagram the contactors are 63 A AC-1 and the cables 10 mm².

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