Sorry about lack of information. The MCB in the distribution board is 3 pole 20A Type D. Then there is one length of 4 core 2.5 sq mm SWA cable, 32 metres long. This goes into a 4 pole isolator, comes out as 4 core flex which goes into the charger. The front panel of the charger has a 3 pole 20A breaker which is used to start/stop the charging cycle. Everything is 3 phase. The black core in the SWA isn't used. While I don't want nuisance tripping, it would be good to know the cable wont melt. Thanks.