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0 pointsjcalvinowens22h ago0 comments

> 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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Dylan1680720h ago

I'm not talking about the safety of different ways of doing three phase. I'm taking it as a given that three phase is wye ground and optimal for safety.

My point is that in the context of a 230V single phase circuit, your ground is no longer in the middle. The ground is on one end of your single phase. If you want a safer single phase, you need to rebalance it to +115 and -115.

jcalvinowensOP17h ago

I thought they meant a "two phase" service where the two phases are 120 degrees out of phase instead of 180, like an apartment fed with two poles of a 208V wye with 120V to neutral/ground, which is balanced. If it's just a single phase, you're right.

Dylan1680716h ago

EU power is ~230V on a single phase and ~400V between phases. So a house usually gets three phases, but the only appliance where the voltage to ground is less than the total voltage is probably the oven.

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