The real reason why North America uses 120v instead of 240v.

[tooki]

For what it’s worth, I think the Swiss receptacle system (SN 441011) is extremely elegant: it consists of four receptacle types: 10A and 16A, in single-phase and three-phase. 10A plugs fit into 16A sockets (not so special), but the thing that is unique (as far as I’m aware) is that single-phase plugs fit into three-phase sockets.

This is extremely practical, for example in laundry rooms, which often have three-phase sockets for the washer and dryer, but which then accept a modern single-phase heat pump dryer without any adapters.

Standard 2-pin Europlugs (CEE-7/16, 2.5A) fit into them, too (the standard requires sockets to accommodate them) but not standard European grounded CEE 7/7 (Schuko/F) or the 16A 2-pin (CEE-7/17) European plug.

Old versions of the standard had some exposed-metal hazards, but sleeved pins have been required for years, and recessed sockets are now required for all new installations. (In the past they were required only in wet spaces.)

It’s curious that all of the newest outlet standards (like the new ones in Brazil and South Africa) are based on the IEC 60906-1 socket, which itself is a tweaked version of the Swiss socket. (All mutually incompatible, of course…)

[Zero999]

In italy there should still be some areas in Turin and Rome with three phase 230V, no neutral (residential utilities are connected between two phases)
however the last i heard of it is that they started converting to the current 400V 3phase + neutral

I know Belgium is similar, in rural areas.
Apparently some electric vehicles cannot charge off such 230V 3ph, they require a neutral (they will charge on the slow charger, but not on a wall box.)

That sounds like bad design to me.

If it was designed properly, it would simply rectify the mains to DC, then power everything from that. It shouldn't be difficult to make a charger which would work from 210VAC to 270VAC single phase, or 210V to 440VAC three phase.

[james_s]

The main advantage I see of 120V is that lower voltage incandescent lamps are substantially more efficient. That is pretty much moot now but for most of the first century of electrification lighting which was primarily incandescent was the largest consumer of electricity. It may be arguably safer, but even 120V can and does kill people. Safety focus should be on preventing shocks more so than surviving them.

[IanB]

That sounds like bad design to me.

If it was designed properly, it would simply rectify the mains to DC, then power everything from that. It shouldn't be difficult to make a charger which would work from 210VAC to 270VAC single phase, or 210V to 440VAC three phase.

There are some special design considerations relating to car chargers concerning the neutral and grounding arrangements, which may be why this limitation exists. I know the neutral is not earth/ground, but I suspect the problem is regulatory rather than technical.

[Siwastaja]

Why not have 120V be 2x 60V to ground? Wouldn't that be the safest way to have 120V?

I found out by coincidence that there is a specific market for construction site power tools, in UK, where it is arranged exactly like this. The argument for it is safety, indeed: they install a step-down transformer to go from 240V to 120V, with a center tap on the output, which is then earthed. Someone who gets shocked between L & earth or N & earth only sees 60VAC, which, while slightly over modern safety limits, is not that dangerous.

I found it out in a project where we wanted to equip a robot supplied by 6s li-ion pack with a powerful construction site vacuum cleaner. So I designed a 22V to 74V (barely below the LVD safety limit for DC) 4-phase 750W boost converter. What next - find a 120V construction vacuum. Not going to order from the USA or Japan due to tight schedule - but quick Googling revealed there exists a complete market for 120V vacuum cleaners and power tools in the UK, so got one from there. And of course, brushed motor vacuum cleaners run from DC just fine, even better than from the AC supply. It was a truly capable solution, with 50cm wide nozzle it picked up quite heavy dirt, gravel etc.

[Zero999]

120VDC is actually on the upper limit for SELV. It still needs basic insulation, but not the same precautions as AC of the same voltage..

I hate those site transformers. They're big and bulky and probably cause more injuries manual handling, than they save by reducing the shock risk. It's much safer to use 230V and an RCD.

[james_s]

120VDC is actually on the upper limit for SELV. It still needs basic insulation, but not the same precautions as AC of the same voltage..

I hate those site transformers. They're big and bulky and probably cause more injuries manual handling, than they save by reducing the shock risk. It's much safer to use 230V and an RCD.

I suspect the transformers came along a lot sooner and the regulations just never changed, there's a lot of inertia in that sort of thing. It's a lot easier to make a new law than to get rid of an old one that isn't really needed anymore.

[AVGresponding]

120VDC is actually on the upper limit for SELV. It still needs basic insulation, but not the same precautions as AC of the same voltage..

I hate those site transformers. They're big and bulky and probably cause more injuries manual handling, than they save by reducing the shock risk. It's much safer to use 230V and an RCD.

Yes, but we were talking about AC, not DC. The limit for AC is 50V.

[Zero999]

120VDC is actually on the upper limit for SELV. It still needs basic insulation, but not the same precautions as AC of the same voltage..

I hate those site transformers. They're big and bulky and probably cause more injuries manual handling, than they save by reducing the shock risk. It's much safer to use 230V and an RCD.

Yes, but we were talking about AC, not DC. The limit for AC is 50V.

I know. If you read Siwastaja's post, which I was responding to, you'll find he was using 120V DC.

[AVGresponding]

120VDC is actually on the upper limit for SELV. It still needs basic insulation, but not the same precautions as AC of the same voltage..

I hate those site transformers. They're big and bulky and probably cause more injuries manual handling, than they save by reducing the shock risk. It's much safer to use 230V and an RCD.

Yes, but we were talking about AC, not DC. The limit for AC is 50V.

I know. If you read Siwastaja's post, which I was responding to, you'll find he was using 120V DC.

Perhaps the confusion arose from their mistake regarding the nominal voltage of construction site equipment in the UK, and from the fact they are not clear about the actual voltage they are putting through the 110VAC appliance they are using.