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0 pointsjcalvinowens1d ago0 comments

> When the system is AC ground makes no difference.

With AC it's about where the ground is attached along the length of the transformer secondary. In the EU they ground one of the ends of the secondary, in the US we ground the center point.

I don't get to say this very often ... but the US way is objectively safer with no downside: 99% of human shocks are via ground, and it halves the voltage to ground (120V vs 240V). A neutral isn't required if there aren't 120V loads.

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Liftyee1d ago

I agree that the US voltage is safer (with the tradeoff of lower output powers available at your outlets). However, I suspect this is more than negated by the US plug design, which carries a much larger risk of shocks than almost all EU plug designs (Schuko, British/Type G, etc...)

- uninsulated metal pins make contact with supply while partially exposed - much smaller distance between metal pins and the edge of the plug

jcalvinowensOP1d ago

100% agree the US plug designs are terrible.

But there's no inherent power tradeoff: you can have 240V outlets in the US, with the two prongs both 120V to ground. They're just really uncommon in residences.

bluGill1d ago

Dryers and Stoves/range outlets are very common in US houses. Of course they are generally hidden behind the device and so most people are not sure if they have them at not. They are also reasonably common in garages (welders, air compressors, table saws... - if your hobby needs them you install them, otherwise you won't have them).

crote1d ago

In the EU it is quite common for houses to have three-phase power. If you squint a bit, the grounded neutral of the Y transformer isn't entirely unlike the grounded center tap in the US. The voltage is a lot higher, of course!

Dylan168071d ago

> If you squint a bit, the grounded neutral of the Y transformer isn't entirely unlike the grounded center tap in the US.

Yes, but you only get the safety benefit on three phase equipment.

In the US there aren't a lot of 240V plugs, but if you get some installed you can get the safety benefits with plain old consumer goods.

jcalvinowensOP9h ago

> but you only get the safety benefit on three phase equipment.

The wye ground is beneficial even if there are no three phase loads, because the line-ground voltage is 1/sqrt(3) and you can use cheaper switchgear.

The 3-phase alternative to a wye ground is a corner ground (grounding a live phase of a delta secondary), which isn't done in modern installations because ground faults are full line-line voltage and you need more expensive switchgear.

Line-line faults are always interrupted by two breakers on a wye grounded 3 phase system. But with a corner ground, one breaker potentially has to break the full line voltage for a line-ground fault (you can't fuse the grounded phase).

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