Assuming a 3 phase 400A DNO underground 300wf Ai/Cu cable to an (HDCU) Heavy Duty cut out located in a cubicle in a Car Park. A DNO earth is not provided. Double insulated 185mm Meter Tails run from the HDCU to a sw/fused isolator then onto a bussbar chamber feeding 3 x 250Amp rated Type B D/Boards. 13 Electric Vehicle Charger Circuits will be installed from each of the 3no D/Boards so 39 circuits in total. A TT Earth Electrode shall be located next to the cubicle with the consumer earth connected from the electrode directly to the switchgear within the cubicle thus forming it's own TT System. All 39 EVC Circuits shall be 3 phase and protected by 30mA Type A RCBOs mounted in each of the D/Boards.
Am I correct assuming the RCBOs must all be 4 pole because the Neutral is classed as a line conductor? If using Schneider the Acti 9 type requires 6 ways per circuit when using the bolt on RCD element.
Also should each of the D/Boards have a time delay S-Type RCD acting as a Main Switch or will a standard 4 pole dissconnector suffice as a Main Switch?
