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Topic Title: change over switch for geni
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Created On: 24 July 2012 10:20 PM
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 24 July 2012 10:20 PM
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Joined: 07 February 2007

Hi all

have been aprouched to install a small suit case Geni to a house with P.V.
the suit case is to run lights and a boiler but my concerns are with the P.V supply back feeding through the geni.the customer said he will be turning of non essential circuits but I have heard than before.

my question realy is will the P.V
1st will the inverter be damaged by the geni's unsmoothed sin wave ect
2nd will the inverters produced voltages produced by day time use damage the geni
any advice please
 24 July 2012 11:41 PM
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The PV expects to be able to export to the mains if local load doesn't outstrip PV generation - it won't (prettily) be able to export to the generator.

I think I'd expect the PV to be connected to the mains (DNO) side of the change-over switch, so during the power cut all power comes from the generator and the PV inverter just sits there and sulks.

Either that or go for an off-grid PV setup - complete with big & expensive storage batteries, but economically it's unlikely to be worth it if mains is (normally) available.

- Andy.
 25 July 2012 07:57 AM
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if you are installing a 4 pole chang-over switch the PV MUST be conncected the suppliers incoming side of the change-over switch and NOT the common side of the switch.

Therefore in the event of a power failure the inverter will switch off to prevent back feeding, its the same old story, if you have a power failure your PV wont help you it just shuts down
 25 July 2012 10:01 AM
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thanks for the info lads
I think I will have a shuffle around with the existing board and have PV on CUT OUT side of change over switch Fused down)
my other option is to have a seperated 2way board fed from the common side of a change over switch and feed 1 side fron a feed from the existing main and a supply from the geni on the other,thus when the change over switch is turn the light,boiler are seperated from existing
 25 July 2012 11:44 AM
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Don't forget to consider what happens to the earthing when running on the generator..... if the current setup is PME then you can't rely on the suppliers earth ... if its TT then you need to consider the earth path back to the generator winding.

When using such a small unit, its unlikey that the existing overcurrent protection will be of any use - the generator is unlikely to to able to provide enough current, even into a dead short, to be able to open the protection in under a week!

Also, in my experience, the PCB control boards of modern boilers dont like the waveform from a little handbag type gennie & rely on a correct earth path for the spark ignition to work properly.

Sorry to burden you with problems... but the use of a small gen to provide a backup supply does come with some interesting .... challenges!


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