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Inverter board - order of switches?


Elbow

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Hi,

 

What's the standard or best practice on an "essential loads" sub-board when I want to have a changeover switch?

I will have the live and neutral coming from the inverter, and a live and neutral coming in from the main supply.

Do I take these two inputs first to my changeover switch, and then put a 2 pole 'sub-main-breaker' after that?

Or do I breaker each one separately and then take the outputs of those two breakers into the changeover switch?

IE (warning, ASCII ART)

 


                                  -----------
FROM MAIN BOARD ---> BREAKER --> |           |
                                 |Changeover |---> to ccts...
FROM INVERTER -----> BREAKER --> |           |
                                  -----------
or
                      -----------
FROM MAIN BOARD ---> |           |
                     |Changeover |---> SUB MAIN BREAKER ---> to ccts...
FROM INVERTER -----> |           |
                      -----------

In the first design the weakness for me is that its not clear which breaker is the "main switch" since it depends on the position of the changeover.  (which FWIW also has a centre off position)

In the second design both incoming feeds would need a breaker at the other end - for the grid feed on the main board and for the inverter feed at the inverter end.  That approach has the weakness that the inverter feed could trip at the inverter side which may not be obvious.  So I suppose the solution is to make sure the breaker on the inverter sub-board has a lower trip current so it trips first.

On the main board there must also be a breaker on the feed to the inverter grid input, sized to protect the cabling (except if this is pure off-grid).

So its coming out like this for me:

MAIN BOARD:                                             INVERTER LOCATION:                             SUB-BOARD:

GRID--->2P MAIN SW  -->BREAKER: TO SUB BOARD---------------------------------------\ 
                    -->BREAKER: TO INVERTER --\                                     \------->|--------|
                                              \->2P ISOLATOR-->INVERTER GRID IN              | C/OVER |-->2P SUB MAIN SW -->BRKR:LIGHTS
                                                 INVERTER OUT-->2P BREAKER: TO SUB BOARD --->|--------|                  -->BRKR:LIGHTS
                                                                                                                         -->RCD-->BRKR:PLUGS
                    -->...                                                                                                     -->BRKR:PLUGS
                    -->RCD-->PLUGS                                                                                             -->...
                          -->PLUGS

Is this OK - there is a single main switch in the sub board but it comes AFTER the changeover switch.

Lastly, where should indicator lights be fitted?  Since there are two supplies into the sub board must there be two indicators on that board?  Or is one after the sub main switch OK?

Thanks

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47 minutes ago, Elbow said:

In the first design the weakness for me is that its not clear which breaker is the "main switch" since it depends on the position of the changeover.  (which FWIW also has a centre off position)

The job of the breaker is to protect the cable. The changeover switch is an isolator at best with no overcurrent protection. So that is the first thing to keep in mind. For the most part I would advise individual breakers to protect each path, and just label them properly so people know that both need to be turned off.

Change-over switches also don't like to be switched under load.

I generally do this:

                                  -----------
FROM MAIN BOARD ---------------> |           |
                                 |Changeover |---> RCD ----> Other circuits
FROM INVERTER -----> BREAKER --> |           |
                                  -----------

In my main board I then have a breaker for the SUB-DB... so that is pretty close to your first option, except I put the breaker from the main board IN the main board.

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56 minutes ago, plonkster said:

I generally do this:


                                  -----------
FROM MAIN BOARD ---------------> |           |
                                 |Changeover |---> RCD ----> Other circuits
FROM INVERTER -----> BREAKER --> |           |
                                  -----------

In my main board I then have a breaker for the SUB-DB... so that is pretty close to your first option, except I put the breaker from the main board IN the main board.

Great, thanks @plonkster

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