length of dc cable run


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brucedownunder2
Guru

Joined: 14/09/2005
Location: Australia
Posts: 1425
Posted: 01:23am 14 Sep 2019      

I've installed 2.5Kw of panels with 3 strings on one lot and 2 strings on the other -both will be 48 volt configuration,

The strings are around 5-7 Mtrs of 6mm solar twin to the breaker box ,which will have 5 mcb's on the positive -all negative feeds will terminate on a brass block.

The Main feed after the breakers for positive and negative will be 10mm sq. double insulated cable in conduit  back 10Mtrs to the solar regulator .

My question is ,and I hope I'm right, will the 10mm sq. feeder cable be within the safe operating limit for 2.5 Kw of panels ...
(I've NEVER seen the full stated output from solar panels and I'm thinking I won't see  2.5 Kw ,maybe 2Kw max )

OK, any thoughts on this particular feed'er question??

Bruce
Bushboy

Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 3260
Posted: 03:21am 14 Sep 2019      

10mm sq is usually rated at 50 amps for normal domestic wiring.

20 Mtrs (there and back) of 10mm sq will have a total resistance of .0344 ohms.
At 50 amps that will drop 1.72 volts.
Cheers, Tony.

brucedownunder2
Guru

Joined: 14/09/2005
Location: Australia
Posts: 1425
Posted: 04:29am 14 Sep 2019      

Thanks Tony ,  

not great, the drop that is , but seeing this is not going to be dependant on gaining every watt, she'll be OK .

 I'm earthing the array under the deck below the panels ,as an independant earth . I thought about connecting into the house electrical ,but the way I'm doing it makes it easy. -none of the end product supply will be connected into the house. It's a completely stand alone system.

having fun with 2.5Kw of second hand panels .  


Bruce
Bushboy

Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 3260
Posted: 10:53pm 14 Sep 2019      

The losses reduce as the available solar reduces, so its not quite as bad as it appears.

Flat out in mid summer, there will probably be more power available than you can use anyway.
Cheers, Tony.