jameshowison
New Member
- Joined
- Jul 30, 2021
- Messages
- 184
In all the diagrams I see the fuse to protect the wire connecting a busbar and the solar charge controller (SCC, MPPT etc) is at the busbar end of the wire, not near the SCC. Given that the power flows from the SCC to the busbar, it seems odd to me that the fuse is at the "far" end. I'm not arguing with it, but I'd like to understand. Any links or threads that discuss this (I tried to search but no luck)? The Victron Wiring Unlimited book shows things this way (but with a marine circuit breaker on the positive of the MPPT) while in the same paragraph saying "Each individual consumer needs to have an individual fuse." See p 31 of https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf
I'm guessing that maybe the protection is really for a situation in which power flows from the busbar to the SCC, but I'm not sure of when that might be (other than a battery short circuit which should be managed by the battery Class T which is placed as close to the battery as possible). Maybe it's just that a SCC is a "consumer" even if it's just voltage from the battery to run the SCC when the sun isn't shining. Maybe the failure situation that the fuse is protecting for is a short in the circuit to the SCC, such as the wires rubbing against each other or the positive with tear in insulation to a chassis creating a short circuit (in which case the power would be flowing from the busbar, through the fuse, to the short, back to the grounding lug, back to the battery (or something).
I notice that some circuit breaker providers (e.g., Midnite solar) advertise "non-polarized" breakers, which I think means they work bi-directionally, but they are still usually depicted closer to the busbar than to the SCC.
So, I think the SCC just isn't able to generate enough current to cause real problems (given appropriate wiring for the panels), and the main cause of problems is the battery, therefore fuse as close to the battery as possible. Is that the thinking? Sure, someone could wire way too many panels up to the SCC but then the SCC will blow up) but that's not the issue being protected for.
I'm guessing that maybe the protection is really for a situation in which power flows from the busbar to the SCC, but I'm not sure of when that might be (other than a battery short circuit which should be managed by the battery Class T which is placed as close to the battery as possible). Maybe it's just that a SCC is a "consumer" even if it's just voltage from the battery to run the SCC when the sun isn't shining. Maybe the failure situation that the fuse is protecting for is a short in the circuit to the SCC, such as the wires rubbing against each other or the positive with tear in insulation to a chassis creating a short circuit (in which case the power would be flowing from the busbar, through the fuse, to the short, back to the grounding lug, back to the battery (or something).
I notice that some circuit breaker providers (e.g., Midnite solar) advertise "non-polarized" breakers, which I think means they work bi-directionally, but they are still usually depicted closer to the busbar than to the SCC.
So, I think the SCC just isn't able to generate enough current to cause real problems (given appropriate wiring for the panels), and the main cause of problems is the battery, therefore fuse as close to the battery as possible. Is that the thinking? Sure, someone could wire way too many panels up to the SCC but then the SCC will blow up) but that's not the issue being protected for.