No no no no, NEVER pull the fuse under load! If you do, even as suggested that you use a multimeter to have alternative path, you will draw an arc (perhaps smaller). This causes your connectors to become “worn” which causes hot spots which (best case) will cause sporadic fuse failures, worst case is burning your house down. I would bet on the worst case scenario.
The correct procedure to see if their is a ground fault:
- Read the MPPT manual, if the system is NRS compliant or VDE standard or sold in Aus, it should have isolation measurements and the inverter or mppt will error or refuse to start up if it detects anything.
- Switch everything off, use a insulation resistance tester (Megger) and test the PV circuit
- Use a I-V curve tracer (preferably with pyranometer).
Point 1, I think is very common and if your inverter isn’t shouting at you, you are most likely safe.
Point 2, is the correct way of finding if there is a problem with your cable insulation to earth
Point 3, this will determine if your panels are still doing what they are supposed to do.
Thermal scanning of all connectors and panels.
Individual panel IV curve testing
At night, multi meter to ground (will most likely not give you much info, really you need the correct tools)
Jacques. If, as you say, you are not trained in this type of work (as this is now becoming a bit specialized) DO NOT DO IT. I cannot stress this enough. There is a point that you need to step away. Even as an electrical engineer, I would step away to let electricians handle certain things. No shame in knowing where your limits are…