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DB Wiring Question



Hi All,

Planning to setup a sunsynk 5.5 inverter. One of the big issues that I am debating is about the wire size and the best route for it.
To run the sunsynk optimal one would need sets of wire( 1 going to inverter and 2 return from inverter). The problem that I have is, I want to install the inverter in the garage but the length is around 20m each way. That will work out to around 60m+ of 6mm2 cable at around R50/60pm it would work out to around R3k just for the wire.

Now my thinking is that the main incoming line of power sits outside the garage, can I split the connection on the outside box of the garage and have a disconnect on the line that goes to the inverter and the original one that goes to the main DB will then still go there?

This is a rough sketch.

Red : Main DB
Brown : Solar panels
Orange : Inverter installation
Yellow : incoming main line box outside garage
Green: Run in the roof
Blue line : Double brick in the roof with holes



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I cant comment on the legality of moving your primary DB but I can tell you that if you have a pre-paid meter, you will need to get this moved by council / certified installer on their behalf and this will most likely cost more in the end than the cabling.

What I can tell you is that 6mm2 cable is not thick enough. A 5.5k inverter will use roughly 26A for which 6mm2 is fine but then you need to take into account spikes which most inverters can handle double their capacity for a very short period of time. This would result in a rough 45 to 50A spike which then requires 10mm2 cable. Over a 60m distance, you will have a voltage drop of roughly 3% and no room for expansion. A 16mm cable would be ideal at 1.9% voltage drop but able to handle 70A

I have just gone through this exercise with upgrading from a 3k to a 5k inverter and needed to replace my existing 6mm2 cable (2x 25m runs). The price difference is not large between 10mm and 16mm. I dont remember what the cabling cost but I do know it was cheaper than the excess on burning the house down due to under-spec'ed cable 🤣 or the labour to re-pull the cable in the future - Sorry

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FYI, to be precise, on the Sunsync 5kW (SA Version)  the essential load is rated at 21.75A and the pass through load at 37A.

Frankly, the marginal cost of using higher rated cable is not worth debating when you're looking at the cost of A decent solar setup.

Edited by FixAMess
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Okay, looks like the 10mm cable will be the best. Might get away with 15m per run.

DB1 to inverter to power inverter 15m

Inverter to DB1 for critical loads 15m

Future plan:

The inverter has a smart ouput where if there is extra solar during the day it can dump into that output. Maybe geyser and pool pump.

How would one wire this to output to the geyser and poolpump to run normally off grid during the day but if there is extra solar run it on that circuit. Or is this where the pass through power rating comes through?

This will then require the 3rd run of 15m from inverter to DB1 geyser/poolpump

Edited by Luminous
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