Also you really, really want to use an all plastic (or plastic and ceramic) trimpot adjuster of the appropriate size. My worst encounter with electricity was adjusting a trimpot in a Sun LC workstation (like an early iMac, computer and monitor together), screwdriver slipped and hit the fly transformer and I went flying several feet and hit the wall, screwdriver had a chunk taken out where it partially vaporized. You might not get thrown by the innards of the EMS, but worse 240V can make you clench up and with 50A coursing through you it's unlikely you're heart would go undamaged.