EV Charging – Tesla specify 6 mA DC fault current detection
25 June 2018
EV charging equipment and cables due to the nature of the environment, storage and use should be maintained and checked regularly to ensure that there is no damage to the equipment and or insulation. In practice equipment may not be checked from one year to the next, and as the equipment ages the probability of a fault developing increases. One of the control measures to reduce the severity of the shock hazard in the event of fault, relies on the correct selection and application of RCDs, to disconnect the circuit under fault conditions.
Tesla specify the use of Doepke’s DFS4 A EV RCCBs with their charge points, to meet the revised safety requirements in IEC61851-1, following the withdrawal of the old standard in July 2017.
The new standard highlights the risks associated with smooth dc fault currents in AC EV charging applications, employing socket-outlets and RCDs for additional protection. IEC61851-1 2017 specifies the use of Type B RCDs or Type A with appropriate equipment that can detect dc fault currents and disconnect the supply, if the fault current exceeds 6 mA dc. Type A EV RCCBs incorporate this functionality and will trip when the 6 mA DC limit is exceeded.
This revised requirement has been introduced to reduce the risks associated with the interpretation of the previous wording of clause 722.531.2.101:
“…The RCD protecting the charging point shall be at least type A… If it is known that the DC component of the residual current exceeds 6 mA then a type B RCD complying with BS EN 62423 shall be installed.. “
It is possible that under the old standard, electric vehicles that can produce smooth DC fault currents above 6 mA, could be connected to charge points containing Type A RCDs, resulting in reduced or lost protection. The new standard removes this ambiguity and the associated risk.
Further information can be found on the Doepke web site. Doepke Technical Publication 06 explains the reasons behind this important safety revision and Type AEV RCDs incorporate this new requirement.
Doepke UK Ltd