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Posted By Topic: Type A-SI RCD for EV charging point

mickydnz
Nov 01 2018 14:13

AS/NZS 3000:2018 clause 7.9.3.3 states that a circuit dedicated for Mode 2 EV charging must be protected by a Type B RCD at the switchboard.

I understand the only reason for this requirement is residual smooth DC current could be present in the circuit as a result of the rectifier in the car (steady state or during faults). Type A RCDs can only tolerate up to 6mA of smooth DC residual current before they become blinded due to saturation.

A Type B RCD is already installed in the EVSE to provide protection for DC earth faults in the car.

I recently learned about Type A-SI RCDs which are immune to smooth DC residual current up to 60mA and provide the normal Type A AC and pulsed DC protection for the circuit.

Why should I pay ~$1000 for a switchboard mounted Type B RCD to provide smooth DC earth fault protection on the installation wiring and socket/plug up to the EVSE when this type of fault is impossible at these locations? A type A-SI should be sufficient but is prohibited by AS/NZS 3000:2018.

Any comments?
http://www.electrical-installation.org/enwiki/Coordination_of_residual_current_protective_devices#Specific_case_for_the_coordination_with_RCDs_type_B
   

dbuckley
Nov 01 2018 15:58

A question that bugs me is why DC sensitive RCD is required at all, as for Mode 2 there is a suitable RCD incorporated in the cable.

Some of these in-cable RCDs even disconnect the earth connection, which is a really sensible idea.
   

gregmcc
Nov 01 2018 17:41

keep in mind AS/NZS3000:2018 is not cited in NZ law yet, we still use 3000:2007
   

ppaw1965
Nov 01 2018 21:15

From past experience the type B is less likely to trip than the type Si
   

pluto
Nov 01 2018 22:14

The most important parts in the selection of the correct RCD.

Itg concerns the amount of d.c. rsidual current flowing in ther protective earth to the high power electronics, which is verry hard to advoid.

I am off shore at the moment on standards and will reply on my return.

A figure of 60 mA above for residusl d.c. currents is well off the expected level of current of around 10 mA max.