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by dbcurtis 2778 days ago
> Transformer explosions are inherently harder to isolate from flammable material in the American distribution system design than they would be in a European 240v system, that's because the US system has to keep LV (110v) runs short so has extensive HV networks with pole-mounted transformers feeding a small number of properties each. 240v systems can tolerate longer LV runs and use larger pad-mounted distribution

Wait... In the US for household single-phase it is 240V from the pole transformer to the breaker panel, where the 120V is derived by taking one hot or the other against the neutral, and the range/drier/etc 240V circuits are simply across both hots. So there is no difference between EU or US distribution voltages until it gets inside the house. All the US does is add a neutral so that it is easy to get 120V.
1 comments
Mvandenbergh 2778 days ago
UK is 400v phase-phase and 230v phase-neutral. The distribution transformers are three-phase out and the LV main serving a street is 3 phase wires and a neutral, each house is fed from one of the phases and connected to the neutral.

My understanding of the standard US system is that the distribution transformer is fed with one phase, the secondary side of the transformer has a centre-tap neutral and two live phases which have 120v to neutral and 240v phase-phase.

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dbcurtis 2778 days ago
> UK is 400v phase-phase and 230v phase-neutral. The distribution transformers are three-phase out and the LV main serving a street is 3 phase wires and a neutral, each house is fed from one of the phases and connected to the neutral.

Good to know.

> My understanding of the standard US system is that the distribution transformer is fed with one phase, the secondary side of the transformer has a centre-tap neutral and two live phases which have 120v to neutral and 240v phase-phase.

yes

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planteen 2778 days ago
Three-phase power is common for service in the US for commercial, industrial, and rural areas. But it is not typical in urban or suburban residential areas.

And yes, nearly every home is served by 220 V phase-to-phase with a center tap. Am I understanding right that UK houses are only fed by single phase at 230 V with neutral?

Is the reason we have pole mounted transformers in the US really because of voltage drop though? It seems to me the reason would be they are inherently smaller due to the lower voltages, higher frequency, and only converting one phase from the distribution side. The UK has lower frequency, higher voltage, and apparently has three output phases which seems like it would require a larger transformer.

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Mvandenbergh 2778 days ago
>Am I understanding right that UK houses are only fed by single phase at 230 V with neutral?

That's right, typically houses along a street will alternate phases to maintain overall balance. Standard used to be 60A supply but is now 100A which I believe would be considered low in the US but we don't usually have residential air conditioners and houses are smaller and heated with gas.

I have been told that this is the reason but there are other reasons to prefer the US arrangement so it may not be the only one. US system is more resilient to secondary failure because fewer customers are fed per secondary and you have a much more extensive HV network which is more flexible.

UK distribution transformers are much, much larger. Looks like this: https://cms.esi.info/Media/productImages/Expanded_Metal_Comp... My point was that it is easier to enclose a smaller number of large assets than a large number of small ones which is relevant to fire risk.

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