Author Topic: The real reason why North America uses 120v instead of 240v.  (Read 13491 times)

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Online bdunham7

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #25 on: November 24, 2022, 10:06:08 pm »
Where's the data to suggest 120V systems and, as I originally stated, the accompanying attitudes regarding safety, are in fact safer?

I see no reason to think that certain attitudes 'accompany' 120V  systems and don't know why you'd lump them somehow as if Americans are less worried about shocks because the voltage is lower.  Would you be more likely to ignore the railway crossing lights if the train was a passenger train vs a freight train? 

What I said was that I don't think you are going to be able to tease out meaningful data that really shows you that one voltage is safer than the others using shock fatality stats from two different areas with other variables in play.  IOW, your statistics are meaningless for this purpose, IMO.  It could be that Americans, due to stupidity and neglect, get shocked 300X more often by 120V than Brits do by 240V, but only have 4X the fatality rate.  That would make 120V 75X safer.  Or maybe not.
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Offline Monkeh

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #26 on: November 24, 2022, 10:15:44 pm »
Where's the data to suggest 120V systems and, as I originally stated, the accompanying attitudes regarding safety, are in fact safer?

I see no reason to think that certain attitudes 'accompany' 120V  systems

https://www.eevblog.com/forum/projects/can-i-convert-a-atx-psu-to-run-directly-off-of-12v/msg4498369/#msg4498369

That's far from my only personal experience of how people treat 120V systems as 'safe' because it is 'safer'.

Quote
Would you be more likely to ignore the railway crossing lights if the train was a passenger train vs a freight train?

I have just recently seen someone step out in front of a learner driver because they believe the instructor will stop them. So yes, people will treat dangerous situations differently based upon their misguided preconceptions.

Quote
What I said was that I don't think you are going to be able to tease out meaningful data that really shows you that one voltage is safer than the others using shock fatality stats from two different areas with other variables in play.  IOW, your statistics are meaningless for this purpose, IMO.  It could be that Americans, due to stupidity and neglect, get shocked 300X more often by 120V than Brits do by 240V, but only have 4X the fatality rate.  That would make 120V 75X safer.  Or maybe not.

And I agree that it isn't easy to draw conclusions from the data - but I find it unlikely that the most commonly accessible voltage is in fact safer when fatalities are 20-30x higher for only 6x the population.
 
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Online themadhippy

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #27 on: November 24, 2022, 10:30:21 pm »
maybe its down the shite quality of electrical work,look at the state of the american fuse boards posted in the "show your fuse board " thread,or compare the popular uk electrical youtube channels with american equivalent.Take a typical american electrical accessory,its either stab and pray,or wrap the wire around an exposed screw, or there the love of wire nuts.
 

Offline mcovington

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #28 on: November 24, 2022, 11:19:35 pm »
There are at least 4 safety differences.

(1) 120 V is supposedly less lethal than 240 V, but I don't know if the difference is significant in practice.  I wouldn't want to be shocked by either one. 

(2) 240 V requires half as many amps to deliver the same amount of power, and thus, only 1/4 as much heat dissipated in a poor connection.

(3) To further mitigate the effect of poor connections in house wiring, Britain, as I understand it, commonly uses ring arrangements where there are two paths from source to load; North American never does.  (Is it even permissible in North America?  Does Australia use it?)

(4) Fuses in plugs or outlets and switches on outlets are, as I understand it, usual in the UK (also Aus?) but rare in North America.

As well as someone mentioned that in 240 V countries, both sides of the power line are expected to be well insulated from anything the user can contact.  (That is a reasonable expectation and normal practice in North America as well; I wouldn't build anything any other way.)
 

Offline Monkeh

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #29 on: November 24, 2022, 11:24:14 pm »
(3) To further mitigate the effect of poor connections in house wiring, Britain, as I understand it, commonly uses ring arrangements where there are two paths from source to load; North American never does.  (Is it even permissible in North America?  Does Australia use it?)

Double edged sword. The purpose is actually to reduce the amount of copper needed to provide flexible placement of loads - specifically, electric heaters. It's a bit out of date these days. While it will reduce the risk of fire from a single loose connection, it also hides the symptoms of said loose connection and can lead to excessive current in one leg for prolonged periods.

Basically unused outside of the UK and a few territories.
 
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Offline nightfire

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #30 on: November 24, 2022, 11:39:55 pm »
To put some stuff as further things in the fire:

The human adult body (depending on the path the current flows) is roughly 1000R-2000R. So with 120V there is half the amount of current flowing through your body, and maybe (as it needs some initial voltage to begin going through your skin) in some cases of thick skin a complete accident would have been avoided.
so 120V/2000 Ohms=60mA ->way more than the 10mA that are regarded as the area where it gets realllly sticky.

When it comes to regulations, it also is important who controls these and who trains the people that do the installation stuff. Here in germany as an electrician, you have to do a longer apprenticeship than most other trades, its 3.5 years. After the exam you still need some masters degree to be able to really run a company alone due to some regulations. Also regarding workspace safety, both by law and by your workplace insurers it is mandated that you have to do some danger assessment of your equipment and regular (read: yearly) testing of your appliances. If you have low stress on them, like PC in an office, you can prolong that to every two years.
So the awareness for safety is a bit higher, and you have ready access to qualfied people.
When you live in an area that is sparsely populated, lots of people are DIY, and thats where potential issues occur. Or people cheap out on quality parts etc.

I also read a statistic from a (i think french) power company where lots of maintenance things were done with trained people under live voltage, and the accidents decreased. Reason: You are aware of the danger and plan accordingly, because one big cause of accidents is routine with experienced people.

Also lots of injuries from electric accidents as the root cause do not originate from the voltage itself, but from surprise and a secondary accident like falling from a ladder. Depending on how this is counted, it also might affect the numbers quite a bit, especially when lots of people in the US due to lack of health insurance avoid going directly to the hospital or doctor.
 

Online bdunham7

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #31 on: November 24, 2022, 11:54:19 pm »
And I agree that it isn't easy to draw conclusions from the data - but I find it unlikely that the most commonly accessible voltage is in fact safer when fatalities are 20-30x higher for only 6x the population.

Hmmm.   Perhaps you haven't met enough of my fellow Americans.  Or seen how some clowns wired my house.
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Online thm_w

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #32 on: November 24, 2022, 11:56:51 pm »
@Monkeh,

If you have so many sources, it should be easy for you to cite at least two comparisons.  So?

And your source that 120V actually works out safer in practice? Thought not.

https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/deaths/adhocs/14400deathswhereicd10codesw86orw87wererecordedastheunderlyingcauseengland2019to2020registrations
https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/Electrical/osFatalElectricalInjuries.pdf

UK is actually lower than Canada in terms of electrocution deaths as well (~50%).
Although both are very low overall, 13 for UK per year is nothing compared to other causes (obesity 31k+).

Maybe the shrouded plugs and safety shutters help a bit.
« Last Edit: November 24, 2022, 11:58:32 pm by thm_w »
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Online coppice

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #33 on: November 25, 2022, 12:01:16 am »
Do countries that use 240V have two out-of-phase 120V lines (like the US actually has), or do they just have a single 240V line?
Most countries that supply 220V to 240V power use a single phase. However, I know one country which supplies only 220V power (no 110V or 120V) as two out of phase lines - the Philippines. You have to be a bit careful working on stuff there. Its easy to forget that neither wire is close to ground.
 
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Offline Monkeh

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #34 on: November 25, 2022, 12:02:42 am »
And I agree that it isn't easy to draw conclusions from the data - but I find it unlikely that the most commonly accessible voltage is in fact safer when fatalities are 20-30x higher for only 6x the population.

Hmmm.   Perhaps you haven't met enough of my fellow Americans.  Or seen how some clowns wired my house.

I've seen what passes for professionally installed wiring in brand new homes, which is bad enough. Refers straight back to my point on accompanying attitudes.

UK is actually lower than Canada in terms of electrocution deaths as well (~50%).

Is that adjusted for population or absolute? Because the population of England is 50% greater than Canada.
 

Online thm_w

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #35 on: November 25, 2022, 12:10:13 am »
UK is actually lower than Canada in terms of electrocution deaths as well (~50%).

Is that adjusted for population or absolute? Because the population of England is 50% greater than Canada.

Yes, that was based off the Ontario number of 5 deaths, which has a population about 4x less than England.
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Offline IanB

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #36 on: November 25, 2022, 12:16:37 am »
I've seen what passes for professionally installed wiring in brand new homes, which is bad enough. Refers straight back to my point on accompanying attitudes.

New homes are going to be the worst, especially when they are part of a large development. When they have dozens or hundreds of homes to build, they are going to do each one as quickly and cheaply as possible. That's why there is "back stab" wiring in the USA. The apprentice who gets to wire up all the light switches and sockets doesn't even need a screwdriver to do the wiring. Just strip the insulation, stab the wire into the terminal, and done. (Mind you, I see Wago learned from that, as there are now push fit Wago connectors.)

Another thing that really annoys me is when said apprentice uses a power driver to do up the screws on the receptacle and strips the threads by over torqueing. Nearly all the wall boxes in my house have had their threads stripped like that.
 

Offline Monkeh

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #37 on: November 25, 2022, 12:29:33 am »
I've seen what passes for professionally installed wiring in brand new homes, which is bad enough. Refers straight back to my point on accompanying attitudes.

New homes are going to be the worst, especially when they are part of a large development. When they have dozens or hundreds of homes to build, they are going to do each one as quickly and cheaply as possible. That's why there is "back stab" wiring in the USA. The apprentice who gets to wire up all the light switches and sockets doesn't even need a screwdriver to do the wiring. Just strip the insulation, stab the wire into the terminal, and done. (Mind you, I see Wago learned from that, as there are now push fit Wago connectors.)

The push-fit Wagos and similar are effectively identical to lever operated types, just without the lever. They're of far higher standard than the crap in receptacles, thankfully - there are meaningful standards applied to them.
 

Offline IanB

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #38 on: November 25, 2022, 12:39:24 am »
The push-fit Wagos and similar are effectively identical to lever operated types, just without the lever. They're of far higher standard than the crap in receptacles, thankfully - there are meaningful standards applied to them.

There is an amusing tier system of receptacles (plug sockets) here in the USA:

"Consumer grade" -- Quite likely to melt and catch fire
"Commercial grade" -- Probably will not catch fire
"Hospital grade" -- Very solidly built, likely to last

There is a corresponding price scale, which means few people are going to spend the money on hospital grade items.

Guess what gets installed in new homes?

(Also, guess why the latest electrical code insists on arc fault circuit interrupters?)
« Last Edit: November 25, 2022, 12:41:05 am by IanB »
 

Online Someone

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #39 on: November 25, 2022, 01:58:13 am »
Ok, here is a topic I know quite a bit about. Household mains in Australia, although 240V (the more dangerous kind) is a vanishingly small proportion of electrical deaths:
https://www.erac.gov.au
>95% of deaths are from distribution infrastructure, only a tiny percent are from interaction with 240V.

We do have international standards for electrical hazards like the Test and Measurement standard 61010. That has within it various graphs for "acceptable" exposures:
maximum single fault duration (dry conditions): 110V AC 200ms, 240V AC 40ms, 5x shorter exposure
normal (non fault) accessible capacitance: 110V DC 4uF 24mJ, 240V DC 1.5uF 43mJ, higher energy permissible for higher voltage!
It is not always a clear cut more = worse, or a steady relationship. How about:
"Effects of current on human beings and livestock" IEC 60479
Median body impedance, hand to hand (dry): 100V 1725ohm 60mA, 225V 1225ohm 200mA

Its those (median) currents where the difference lies. 110V is unlikely to produce heart or breathing arrest even with a sustained exposure, while 240V is almost certainly going to interrupt essential body functions unless the exposure is limited in duration to only a few to a dozen cycles of the line frequency.

Hence residual current devices cutting off power in 200ms (matching the 240V line for the 60479 standard) and them being mandated in all consumer settings.
 

Online Someone

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #40 on: November 25, 2022, 02:01:30 am »
The push-fit Wagos and similar are effectively identical to lever operated types, just without the lever. They're of far higher standard than the crap in receptacles, thankfully - there are meaningful standards applied to them.
There is an amusing tier system of receptacles (plug sockets) here in the USA:

"Consumer grade" -- Quite likely to melt and catch fire
"Commercial grade" -- Probably will not catch fire
"Hospital grade" -- Very solidly built, likely to last

There is a corresponding price scale, which means few people are going to spend the money on hospital grade items.

Guess what gets installed in new homes?

(Also, guess why the latest electrical code insists on arc fault circuit interrupters?)
This is the downside of 110V delivery, increased risk of fire from the electrical installation. Such fires are barely evident in 240V systems historically, but widespread multi kW vehicle charging will likely change that!
 

Offline IanB

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #41 on: November 25, 2022, 02:55:21 am »
This is the downside of 110V delivery, increased risk of fire from the electrical installation. Such fires are barely evident in 240V systems historically, but widespread multi kW vehicle charging will likely change that!

It's more a question of quality control. For instance, I have a 1500 W electric kettle, which has a figure 8 zip cord and moulded on plug. When I use the kettle, the plug gets notably warm, even hot, where the cable joins it. I'm not sure what kind of connection exists between the conductors and the plug pins hidden inside the plastic moulding, but I don't think it is very good. Soldered? Crimped? I have my doubts.
 

Offline Siwastaja

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #42 on: November 25, 2022, 10:13:11 am »
North America does not use "120V instead of 240V". North America uses BOTH 120V and 240V. It's a pretty clever system although one could claim ours is simpler, with one voltage and one plug. OTOH, our plug is limited to ~2.5kW continuous. Households in the US of A have higher-power sockets available, if not in every room, but at least a few in the house!
 

Offline jonpaul

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #43 on: November 25, 2022, 10:23:19 am »

My recollection...

Thomas Edison setup first electrical distribution in 1880s Pearl St DC generators serving lower Manhattan.
The gutta percha insulation led to 100V tension.

Later, the industry advanced to AC distribution, the service voltage was increased to 120V to compensate for copper losses.

Nowadays Con Edison has a 12 kV mesh underground network, with 12 k to 240V/ 120 single phase or 208 V delta three phase.

Just the ramblings of an old retired EE

Jon
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Offline snarkysparky

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #44 on: November 25, 2022, 11:18:22 am »
My guess is that the vast majority of electrical shock fatalities are in industrial settings.  480 VAC and much higher.

So unless there is data that breaks our household electrical shock fatalities the data is meaningless to the discussion.

Also i would guess there is some nonlinear effect in the current induced by the voltage.   48 VAC is unlikely to provide more than a tingle unless wet.  120 VAC could be just an annoyance.  Many electricians in the USA test for hot on 120 VAC by lightly touching the wires.  Step up to 480 VAC ( which is 277 to ground)  and things become much more serious.

In Britain what is the voltage to earth in their systems?
 

Offline pcprogrammer

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #45 on: November 25, 2022, 11:40:41 am »
All I can draw from my own experience is that I sure did get shocked quite a few times with 220V in my life and always got a strong withdrawal reflex with no more consequence than an elevated heart rate for a couple minutes.

I can relate to that :o

Had my fair share of shocks and never had a contracting muscle experience. Not even in a controlled environment where I was pushed forward as volunteer test subject to show that this is the risk of electricity. The instructor strapped a conductive belt around my arm and handed me a pair of pliers. Both wired to a variac. He started turning up the voltage, and at some point the tingle became to strong so I let go of the pliers. Not the result he hoped to get  :-DD

Another time was, when I was helping out a friend with some remodeling. Needed to remove some light fixtures. Disconnected the assumed live wire and started removing the lights. At some point I felt some tingling sensation, and thought, this is strange. Went to the box with the mains connection and it turned out some joker had swapped the live and neutral wires :palm:

Offline Tangent_Tracker

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #46 on: November 25, 2022, 11:55:28 am »
Do countries that use 240V have two out-of-phase 120V lines (like the US actually has), or do they just have a single 240V line?

It is single phase 240 V, but wiring and appliances are supposed to assume that both line and neutral conductors are live, and each has to be equally insulated from any exposed parts that could be touched.

We certainly have the safest plug and socket system in the world I think. That is our saving grace.
 

Online tom66

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #47 on: November 25, 2022, 12:12:17 pm »
This is the downside of 110V delivery, increased risk of fire from the electrical installation. Such fires are barely evident in 240V systems historically, but widespread multi kW vehicle charging will likely change that!

Apologies if I'm misreading you, but since most EVs are charged from 240V will there be much of a difference here between the US and elsewhere?
 

Online Someone

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #48 on: November 25, 2022, 12:46:55 pm »
This is the downside of 110V delivery, increased risk of fire from the electrical installation. Such fires are barely evident in 240V systems historically, but widespread multi kW vehicle charging will likely change that!
Apologies if I'm misreading you, but since most EVs are charged from 240V will there be much of a difference here between the US and elsewhere?
Few people experience joule heating in day to day 240V appliance wiring (or household wiring) because there is ample power at "reasonable" current. But high power EV charging includes thermal management for the cabling! Hot cables are something new for consumers and the "clever idiot" will find some way to defeat the safety systems and/or plug into normal circuits (normal here and in the UK for a set of power points to have a breaker rated higher than any single point could safely supply).

Domestic fires from electrical distribution faults are still unusual in Australia, but the thermal sources are changing:
https://rac.com.au/home-life/info/house-fire-causes
Lithium battery charging is becoming a noticeable cause of house fires (we'd guess from junk cells and inappropriate charging).

Where as US data has arcing of fixed wiring as the major cause:
https://www.nfpa.org/News-and-Research/Data-research-and-tools/Electrical/Electrical
Is that from relaxed regulations/compliance/enforcement or the lower voltage? Probably both.

PS. get smoke alarms, they really do save lives for little cost.
 

Online NiHaoMike

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Re: The real reason why North America uses 120v instead of 240v.
« Reply #49 on: November 25, 2022, 01:25:18 pm »
Why not have 120V be 2x 60V to ground? Wouldn't that be the safest way to have 120V?
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