Cable sizing question

DIY
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1

Would appreciate advice around cabling sizing for system comprised of:

4 x Multiplus II 48/5000 paralleled (single phase)
3 x MPPT 250/100 Tr networked via VE Can
8 x Pylontech US5000B
Cerbo-GX device

I understand that cable size must be identical for each of the inverters. But do I need to use the same size cable on the MPPTs too? Or is it sufficient that the MPPTs all share one cable size and the Multis all share one cable size?

The recommended cable size for the multis is 70mm but the connector on the MPPTs only accepts up to 35mm.

Thanks in advance for your feedback.

2

The cable size for the multiplus is to reduce ripple not for current capacity. The size is important but the length for the inverters needs to be the same. 35mm for the MPPT is fine there will be no ripple. The length should also be the same for each MPPT but I have not had an issue with different lengths using external control on the MPPTs. Hope that helps.

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3

The manual for the MPPT should recommend cable size. You could also do a voltage drip calculation, the Victron Toolkit app includes this.

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The MPPTs do not get a voltage drop but a voltage increase. If the cables are too long the battery might be 56V but the MPPT is seeing 58V. It does not matter if they are externally controlled they just send the current the system allows. The MPPT cable size does matter for standalone if you want the MPPT to use its voltage reading. Most setups will use a battery sense or shunt voltage close to the battery and share that with the MPPT.

Just use the biggest cable you can fit in there.