I was using the MC4 3 way connectors but only one connected--Leaving 2 male connectors exposed--After a month my inverter would give "ERROR 51" and shut down--The problem was traced to the MC4 connector that made a short on my Aluzink roof burning a hole as big as a 5c through the roof -Panels are earthed at the roof and a seperate earth spike was installed--And so I am learning something new every day

Big oooof... that's rough, so sorry. I myself tend towards combiner boxes over splitters for this reason. Had someone start a fire right next to their inverter because of these coupled with a lightning strike, the fuses and surge arrestors inside of a combiner box would have saved him having to replace the entire inverter (write-off due to excessive repair costs). Since that day, nothing but combiner boxes for PV management and connection for me...