So Earth cable size for the DC side of a grid tied installation for multiplus 2 8000kVa 48V, two MPPT 250/85, and a 16kWh battery.
I recall reading that the Earth cable size needs to be the same as the pos and neg cable size from the battery, which in my case are 2 x 50mm2 each.
So can anybody confirm that I need 2 x 50mm2 Earth cable for all the DC earthing requirements (Inverter to Lynx and MPPT (via an Earth busbar).
At the moment I just have 16mm2 Earth cable.
Edit - I just found this in the wiring documents, says Earth cable needs to carry fault current at least equal to the DC fuse rating, how can I work out the DC fault current and apply that to the cable size ?, lets assume the fuse is 200A
are you aware of the Victron Toolkit App?
You could use that to determine the needed conductor size (mm²) for a given length and voltage drop.
Manual calculation would be (german mathematical terms):
A=(L x I)/(k x Ua)
A is conductor size in mm²
L is lenght of cable
k is conductivity of cable material (usually copper, which is 57,14 S/m)
Ua is accepted voltage drop in % (in Germany this is usually set to 2%, Victron app states that anything below 3% is safe)
So in your case as an example for 200 Amp fuse, 48 Volt, 2% drop and a lenght of let’s say 3 meters:
A=(3m x 200A)/(57,14S/m x 2% x 48V) = 10.93 mm²
Other way round: If you would accept 3% of voltage drop on earthing cable (which is in my opinion very well acceptable), you can go for a little more than 5 meters from your busbar to every unit to be earthed with your 16 mm² (assuming 200A and 48 Volt).
Have a nice one,
Alex
Edit:
If you use the Victron Toolkit it is assuming DC cabling for supply, not earthing.
Means: they are calculating you cable length twice the length of your input.
For earthing you have to input half the cable lenght into the Toolkit app.
