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EV Charging RCD

Gyaneshwar Kumar

Hi all, 

For a 30 kW DC EV charger on a TN-S system, does the RCD need to disconnect the neutral as well?

The supply is 3-phase + neutral.

The proposed RCD monitors all three phases and neutral but disconnects only the three phases, leaving the neutral connected.

My understanding is that, on a TN-S system where the neutral can reliably be considered to be at earth potential, it is not generally necessary to disconnect the neutral.

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  • 0

    In general you're right - N may be left connected for both ADS and isolation in TN systems. There is however a specific requirement for RCDs for electric vehicle charging installations in 722.531.3.1 "RCDs shall disconnect all live conductors". That said it's not clear to me that for a mode 4 system (i.e. d.c. connection to the vehicle) that you'd need an RCD on the AC side anyway (unless the charger manufacturer requires one).

       - Andy. 

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  • 0

    In general you're right - N may be left connected for both ADS and isolation in TN systems. There is however a specific requirement for RCDs for electric vehicle charging installations in 722.531.3.1 "RCDs shall disconnect all live conductors". That said it's not clear to me that for a mode 4 system (i.e. d.c. connection to the vehicle) that you'd need an RCD on the AC side anyway (unless the charger manufacturer requires one).

       - Andy. 

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  • 0 in reply to AJJewsbury

    Thanks, Andy. I had a chat with the manufacturer, and they advised that while the charger itself has a Type B RCD, it is still advisable to have a Type A RCD on the AC supply side.

    I’m just not sure whether this needs to be 3-pole or 4-pole, and I’m limited on space in the DB to accommodate a 4-pole arrangement.

  • 0 in reply to Gyaneshwar Kumar

    Does the charger need a N?

    If it does, then N will have to run through the RCD (sense coil) anyway otherwise it'll nuisance trip when there's even a minor imbalance.

    If no N, then a 3-pole device would be fine - as all live conductors will be disconnected.

      - Andy.

  • 0 in reply to AJJewsbury

    Yes, it does need Neutral. I was considering schneider 3P+N vigi add on RCD as the RCBO for Isobar DB are limited to 45A. Unlie 3P RCD, the vigi 3P+N monitor/senses all three phases and neutral but breaks only the phases. The 4P vigi add on requires an additional slot. 

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