BYD Atto 3 and a Model 3 off the same single-phase circuit, only 10A GPOs in the garage — heading for an RCD trip?
My partner's Model 3 has been our only EV until last month, charging fine off a granny charger on one of the two 10A GPOs in our garage. Now I've picked up a BYD Atto 3 as well and I'm trying to work out if we can run both cars off granny chargers on the two separate GPOs at the same time overnight, or if that's asking for the RCD to trip. Both cars would be doing their usual midnight to 6am window, roughly 300km a week for the Atto 3 and 200km for the Model 3. Got a quote for a 3-phase upgrade at $8K which feels like a lot just to solve a scheduling problem. Anyone actually run two granny chargers on the same board without issues, or am I underestimating this?
Filed under: Home Charging AU
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9 ANSWERS
@trent_b87July 31, 2026
Two granny chargers pulling close to 10A each is roughly 20A combined, which most single-phase boards carry fine on the main switch — an RCD trip is a fault trip, not an overload trip, so it comes down to whether the circuits and outlets themselves are sound, not whether the board can take the combined draw. What actually matters is whether those two GPOs are on separate circuits. If they're on the same one, that's where I'd be looking first, not the board overall.
How do we actually find that out without getting someone out specifically to check? Or does that always need a sparky at the board regardless of what we try ourselves first?
Always needs someone at the board with a tester unless the circuits happen to be clearly labelled, and most aren't. Twenty minute job, worth doing before you decide anything either way.
@davo9July 30, 2026
Did something adjacent before I added the battery system, two chargers sharing a board. Staggered the start times an hour apart instead of both hitting midnight together, which kept peak draw down without touching the wiring at all.
That's a lot cheaper than the $8K quote if it actually holds up long term. Manual timer plug, or something smarter managing the schedule for you?
Just a basic timer plug on one of the two for now. Not elegant, but at $15 versus $8,000 it bought me time to work out if the bigger upgrade was even worth it.
@hanny_bAugust 03, 2026
We've only ever needed the one charger so can't speak to the two-car version of this, but $8K sounds exactly like the kind of upgrade that's easy to talk yourself into before you've actually hit a real problem.
@shazbot99July 31, 2026
Not your climate probably, but running two loads off one board up here in the wet season, I'd also want to know how hot that switchboard cupboard gets closed up overnight.
@just_lurking22July 30, 2026
we've got the same setup, watching
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